Month: November 2023

Posted on

The differences in CEC metabolism imposed by treatments or species warrant further investigation

The results presented in this dissertation suggest the highly chemical-, species-, and research technique- specific nature of the environmental fate of CECs. For example, cell cultures often form amino acid conjugates while whole plants form sugar conjugates during xenobiotic metabolism. Additionally, more toxicological data are needed on the effects of these and other compounds in terrestrial invertebrates, especially for those of agricultural importance. From the research conducted in this dissertation, future research should focus on the impacts of exposure and the potential for transformation of CECs under different conditions and in multiple species. Future studies should place emphasis on experimentation using bio-solids and TWW with inherent compounds and field conditions to improve environmental relevance. Future risk assessments should be conducted by taking into account the formation of biologically active and conjugated metabolites, and with regard to the potential toxicity of CECs in non-target terrestrial organisms. During the past 3–4 decades, parallel expansions of populations of non-indigenous rhizomatous grasses have occurred in aquatic and estuarine habitats around the nation. Among these expansions are Spartina alterniflora invasions in the salt marshes of the Pacific Northwest , take-over of large sections of the riparian ecosystems in Southern California by Arundo donax and Phragmites australis invasions in the upper regions of salt marshes in the mid-Atlantic states . The east coast salt marsh grass Spartina alterniflora has been invading west coast salt marshes from San Francisco Bay through Washington since the early 1970’s . Although S. alterniflora can produce seeds that are spread by water movement, it spreads mainly through the expansion of its underground rhizomes. In Washington salt marshes, S. alterniflora is large compared to other salt marsh species,blueberry pot size and it is altering ecosystem structure by affecting benthic structure and species diversity .

Likewise, in San Francisco Bay, S. alterniflora displaces the native wetland plants, as well as eelgrasses and algae. In the mid-Atlantic region, Phragmites australis has invaded many wetlands , and replaced much of the upper marsh vegetation, that was characterized by Spartina patens and Distichlis spicata. The 2–3 m tall stems die back at the end of the growing season, but the densely grown shoots remain in place, affecting sedimentation patterns, surrounding less tall vegetation, and use of the marsh by mammals and birds. The rhizomatous grass Arundo donax that in the riparian ecosystems of Southern California has expanded into large, self-sustaining populations, has become an ecological and economical pest. The populations expand through the distribution of vegetative propagules, in the form of stem and rhizome fragments by the rivers. Currently the expansions of rhizomatous grasses like these are combated with mechanical and/or chemical methods. Both these approaches have pros and cons, and their application is affected by the local environmental conditions, funding, and available manpower .The overall goal of this project was to increase the knowledge of the ecophysiology of the internal processes targeted by, or the ecological processes resulting from control efforts, and to facilitate conveyance of this type of information and knowledge to agencies and individuals engaged in control effort of rhizomatous grasses in aquatic and estuarine habitats. The physiological process that we will focus on is allocation of photosynthates to different parts of the plant and the role of internal nitrogen in this process, in order to determine the most effective time for herbicide application.In the hydroponic culture described earlier, the S. alterniflora seedlings that were precultured in deionized water showed an initially slow, but increasing growth, until the growth is reduced near the end of the experiment at week 12 . Specifically, the growth of leaves and stems stopped , as the plants exhaust the N supply from their nutrient solution , and the leaves’ internal N decreases down to their CNC . Before the leaves reached their CNC at the end of week 11, rhizome biomass showed a slow increase to 1.93 + 0.257 g. After the leaves reached their CNC in the last five weeks of the experiment, approximately 6.11 g was added to the rhizome biomass.

While at CNC, internal leaf N content was seen to increase above CNC for a short period, after nutrient additions to the culture solution. In this period, the leaves showed slight biomass increase as well . As the rhizomes grow, new roots and tillers develop at many of their internodes, and the biomass of these tissues show a significant increase , that is related to the increase of S. alterniflora rhizome length.The leaves that were collected from tall and short S. alterniflora in the DE salt marsh, showed differences in the seasonal pattern of the internal N content . At the start of the growing season in March, the leaf N/C ratio in the tall S. alterniflora is high at almost 0.06 g N/gC. In the short S, alterniflora the N/C was lower than both the tall S. alterniflora from the same marsh, and the S. alterniflora in the hydroponic greenhouse experiment early in their growing season . The internal N/C ratio in the leaves of the short S. alterniflora does not change much during the entire growing. In the second half of the growing season, the internal leaf N/C ratios in the tall S, alterniflora leaves decreases and becomes indistinguishable from the N/C ratio in the short S. alterniflora’s leaves.The difference between the growth patterns of the two groups was most pronounced in the growth of the green leaves and the stems. These variables show a reduction in the nitrogen-deprived plants when compared to the plants that continue to receive nitrogen, especially the leaves . In addition to the seemingly smaller amount of above ground plant material, the leaves of the nitrogen-deprived plants were a much lighter color green, and leaf senescence was more common for these plants . As a result of this combination of responses, the nitrogen-deprived plants appeared much smaller than those that continued to receive nitrogen. At the time of reduced leaf growth by the no-nitrogen plants, the internal N content in the nitrogen-deprived plants dropped significantly below the N content in the leaves of the N-supplied plants . This was observed through both the carbon-based and the dry-weight based determination of the tissue N content. The lowest mean N/C ratio was 0.038 + 0.001, and % N dropped below 2%, to 1.69 + 0.052%, at the time that the N content in the leaves of the control plants was lowest as well, with N/C = 0.077 + 0.004 and N = 3.446 + 0.167%.During nitrogen deprivation the growth of mature green leaves was limited or nonexistent, due to lack of mobile nitrogen. Both the function and growth of leaf tissues have a high requirement for nitrogen.

Each functional leaf cell will need to contain a minimum amount of nitrogen for both photosynthetic pigments and enzymes such as chlorophyll and Rubisco, and a full complement of DNA and nucleic acids for RNA production. Once the tissue nitrogen has been diluted to the lowest functional level, also referred to as the Critical Nitrogen Content , each cell will only contain this minimum amount of cellular nitrogen allowing it to function at maintenance level. Therefore these cells will not contain enough nitrogen to produce another complement of DNA and enzymes,blueberry plant size preventing them from dividing and the tissue to grow. During internal nitrogen limitation when leaf biomass did not increase anymore, photosynthesis was not reduced in Ipomoea batatas . Photosynthesis continued after the leaves have reached their CNC and the external nitrogen was depleted. The carbohydrates produced cannot be stored in the leaf tissue since further input of carbon compounds into leaf cells would lower the nitrogen to carbon ratio below their CNC, thus interfering with cell function. Instead of having been incorporated into the leaves, these carbohydrates were translocated to the sinks that are the rhizomes, roots, and for S. alterniflora, the rhizome tip tillers. This S. alterniflora study has shown that growth of that species’ vegetative reproductive structures, the rhizomes, occurs after the internal nitrogen content in the leaves is too low to allow for growth of the leaves. The manufacturers of systemic herbicides advise application of their product when there is substantial translocation to the below ground tissues of the plant. For the control of S. alterniflora to be effective, a systemic herbicide has to be carried in the phloem stream to the below ground permanent structures for winter survival and spring regrowth, the rhizomes and the associated rhizome tip tiller. Most rhizome growth and nearly all growth of rhizome tip tillers occur when the leaf N content has reached its CNC. It is obvious therefore that most photosynthate transport and incorporation in the rhizomes and rhizome tip tillers occurs at the time of low leaf N/C ratios, and not before.

We can expect substantial ‘delivery’ of the active ingredient in systemic herbicides which are carried in the phloem, such as glyphosate, to the target tissues would occur at the time of low leaf N/C. Therefore, it may be beneficial to take leaf N/C ratios into consideration when determining the timing of systemic herbicide applications. The field sampling in this study showed that the leaf N/C ratio of short S. alterniflora that grow away from the creek banks is almost always at its CNC level, while the leaf N/C ratio of the taller plants that grow on the creek banks showed a high level at the beginning of the growing season, and a decrease with time not unlike that of the plants in our greenhouse study. This indicates that our experimental conditions were a reasonable mimic of creek bank salt marsh conditions. Additionally, it indicates that N availability in the fine grained, and anoxic marsh sediment away from the creek banks is significantly different from that in more coarse grained creek bank sediments, through which, rather than over which, the flooding water moves during tidal movements. The low oxygen availability in this marsh sediment may interfere with the uptake of the nutrients, or the nitrogen content of this soil may be lower since exchange between the interstitial soil water and the periodically overlaying nutrient rich sea/marsh water will be limited due to the dense and fine-grained nature of the soil. In a series of studies by our laboratory that observed the role of leaf N content in the allocation of growth on multiple species, the P. australis study was the first in which we controlled the N concentration in the hydroponic nutrient solution. Continuous high concentrations were maintained for all plants until the 11th week of the experiment, at which time the N was removed from the nutrient solution for half of the remaining plants. The growth of the plants in both the no-nitrogen and the nitrogen supplied groups showed the importance of external and internal N on the allocation of growth in P. australis plants. It was interesting that even after the removal of the external N, the plants increased their living biomass by 39 g dry weight, which was almost as much as the 49 g biomass increase of the plants supplied with N. The biomass increase of the plants without external N was most likely supported by the pool of internal N in the plant. At the time the external N supply was removed, the N content in the plants was above their CNC. The critical nitrogen content of a tissue is defined as the lowest amount of nitrogen in tissues that will allow for growth the growth of that tissue. Total plant biomass increased after the removal of the external N, which was evidence that photosynthesis must have continued. As more carbohydrates are produced and incorporated into the plant without an external supply of new nitrogen, the internal N/C ratio in the tissues will decrease. As described earlier, among the different tissues, leaves have the highest CNC, and will therefore reach this CNC earlier than tissues with lower CNC values. When the leaves reached their CNC, they could no longer incorporate more C into their own tissues, since this would reduce their N/C below the CNC and interfere with their function . At this point two scenarios are possible; one is that photosynthesis could shut down, and the other is that all the carbohydrates produced in the leaves could be transported to other tissues of the plant.

Posted on

Polyparabens reportedly inhibited root growth in onion bulbs under hydroponic conditions

Carbamazepine exposure has been seen to exhibit mycotoxicity to carrot mycorrhizal endpoints by decreasing the production of fungal spores . Similarly, carbamazepine induced leaf necrosis, altered plant hormones and macro-nutrient concentrations, and reduced root growth at plant tissue concentrations of 1 to 4 mg kg-1 in zucchini cultivated in soil spiked with chemical at 0.1 – 20 mg kg-1 . Information on the toxicity of benzodiazepines and fluoxetine in terrestrial plants is still limited; however, toxicity has been reported in aquatic plantsfor these compounds, indicating that toxicity may also occur after exposure in terrestrial plants .Antimicrobials and preservatives are often added to personal care products to increase shelf life. They pass from the human body, largely unchanged, and ultimately end up in TWW, bio-solids, and sewage sludge. . Antimicrobials and preservatives have been detected in agricultural soils after irrigation with TWW and/or the application of bio-solids, and can be taken up by plants . Two antimicrobials, triclosan and triclocarban, have attracted more attention because of their potential for endocrine disruption and phytotoxicity . For example, triclosan significantly inhibited plant growth in cucumber and rice seedlings with EC50 of 108 mg kg-1 and 57 mg kg-1 , respectively . Lettuce shoot mass also decreased in a dose-dependent manner after cultivation in soil amended with triclocarban-spiked bio-solids . On the other hand, growth of radish, carrot, soybean, spring wheat, and corn plants grown in soils amended with bio-solids containing environmentally relevant concentrations of triclosan and triclocarban, improved compared to un-amended soils; likely due to the positive impacts of bio-solids addition . Thus, plant species, concentrations, and growth media can significantly affect phytotoxicity of these CECs. Similarly to antimicrobials, parabens have also garnered recent attention due to their potential for endocrine disruption and phytotoxicity . Methyl paraben, the most commonly detected paraben,raspberries in pots has been shown to inhibit seed germination in rice and mung bean in aqueous solutions at respective concentrations of ≥100 mg kg-1 and ≥ 200 mg kg-1 . Methyl paraben decreased shoot growth and biomass in both rice and mung beans at a concentration of ≥ 200 mg kg-1 in soil .

Studies exploring the phytotoxicity of individual pharmaceuticals or classes of pharmaceuticals are useful to highlight high-risk compounds and/or the potential mechanism of toxicity. CECs are, however, often introduced into the environment in complex mixtures and these mixtures can affect the uptake and translocation of individual compounds . Some studies report positive effects on plants exposed to CEC mixtures under environmentally relevant conditions. For instance, TWW irrigation increased tomato and lettuce yield compared to freshwater irrigation . Exposure of lettuce seedlings to a mixture of 11 CECs significantly altered plant metabolic pathways, including the citric acid cycle and pentose phosphate pathway, and decreased chlorophyll content in a dose-dependent manner . Also, exposure to 18 CECs at concentrations ranging from 5 to 50 µg L,-1 induced oxidative stress in cucumber seedlings and caused upregulation of enzymes associated with detoxification reactions . Literature on the toxicity of a number significant CECs to terrestrial plants is still very limited, and many of the studies have utilized concentrations that are orders of magnitude higher than those seen in the environment. Studies on the toxicity of mixtures in terrestrial plants are also limited, but warrant attention as several studies have indicated that mixtures can induce effects not observed from individual compounds . The ability of plants to detoxify these compounds through metabolism also merit further research. Overall, more research is needed on the toxicity of a wider range of CECs in plants under environmentally relevant conditions to more accurately assess the impacts of CECs in the agro-environment. The potential for exposure to, and toxicity of, CECs has been investigated in several aquatic invertebrate species. Toxicity end-points such as endocrine disruption, changes in growth, time to development, and mortality rates have been considered in these studies . Studies addressing the effects of CECs on terrestrial invertebrates are, however, few. Of the published studies on terrestrial invertebrates, the earthworm Eisenia fetida has been examined mainly due to their increased susceptibility andecological importance . Literature pertaining to toxicities of various classes of CECs to terrestrial invertebrates is discussed below. Like in terrestrial plants, antibiotics can also induce toxicity in terrestrial invertebrates. Exposure to environmentally relevant concentrations of antibiotics caused mortality to earthworms and/or induced oxidative stress and genotoxicity in E. fetida. For instance, high concentrations of tetracycline and chlortetracycline inhibited antioxidant enzymes superoxide dismutase and catalase while these enzymes were stimulated at lower doses , and DNA damage was induced along a dose-dependent curve . Also, chlortetracycline can reduced juvenile earthworm and cocoon counts in E. fetida .

Environmentally relevant concentrations of three antibiotics, lincomycin, ciprofloxacin, and oxytetracycline increased mortality and development time in cabbage loopers when reared on an artificial diet and treated tomato plants . Further, the three antibiotics altered the microbiome inside cabbage loopers and mosquitos but did not impact development time of mosquitoes . However, antibiotic exposure did not induce toxicity in aphids reared on bell peppers . Antibiotic toxicity in terrestrial invertebrates, therefore, appears to depends upon the specific antibiotics, concentrations, bioavailability, invertebrate species, and environmental conditions.Exposure to NSAIDs caused acute and sub-acute adverse effects in terrestrial invertebrates, including earthworms . Pino et al. assessed lethality of E. fetida cultivated in artificial soil as a result of exposure to 18 pharmaceuticals. Ibuprofen had the lowest LC50 at 64.8 mg kg-1 followed by diclofenac at 90.5 mg kg-1 . Exposure to diclofenac resulted in a dose-dependent decrease in survival and reproduction of Folsomia candida in spiked soils . However, it should be noted that these LC50 values were much higher than what may be expected in the real environment. At sub-acute concentrations , diclofenac induced significant genotoxicity in Folsomia candida, including induction of the up-regulation of transcriptional processes and genes associated with the immune response . Acetaminophen increased E. fetida mortality along both a dose-dependent curve and over time [7-28 d ]. In the mosquito species Culex quinquefasciatus, exposure to water contaminated with an environmentally relevant concentration of acetaminophen resulted in increased susceptibility to Bacillus thuringien israelensis and increased larval development time . Acetaminophen at environmentally relevant concentrations also significantly increased days to adulthood in cabbage loopers reared on an artificial diet. However, a similar effect was not observed when cabbage loopers were reared on acetaminophen-treated tomato plants . Similarly, the development time for aphids reared on acetaminophen treated bell pepper was not affected by acetaminophen . Therefore, like for other CECs, effeccts of NSAIDs on terrestrial invertebrates are species, compound, and environment specific.

Many antimicrobials and preservatives, including the common environmental contaminants triclocarban, triclosan, and parabens are amongst the most frequently detected in TWW and bio-solids . Partitioning of these CECs into bio-solids suggests that soil-dwelling organisms are at greater risks of exposure as they preferentially consume organic matter rich soils and bio-solids . Triclocarban, triclosan, and methyl-triclosan have been detected in the tissues of earthworms collected from field sites that were amended with bio-solids 4 years prior to the worm collection . After 28-d exposure to triclosan at ≥50 mg kg-1 in soil E. fetida had significantly increased SOD and CAT activities and increased concentrations of malondialdehyde , a chemical indicative of lipid peroxidation and DNA damage in E. fetida . Lin et al. reported negative impacts of triclosan exposure on E. fetida reproduction including decreases in the number of cocoons and juveniles. Triclosan also decreased the biomass, shell diameter,blueberries in containers growing and food intake in a terrestrial snail at concentrations ≥ 40 mg kg-1 . Further, triclosan exposure increased CAT and SOD activities and MDA concentration in A. fulica in a dose-dependent manner . However, no adverse effects were observed in E. fetida cultivated in triclosan-amended bio-solids at environmentally relevant concentrations . Triclocarban is more persistent in the environment than triclosan and is known to bio-accumulate in earthworm tissues . However, information on its toxicity to terrestrial invertebrates remains limited. For example, in Synder et al. exposure to triclocarban at concentrations ≥ 77 mg kg-1 for 2-4 weeks resulted in a trend towards increased mortality; however, the variations in data were too high to discern any statistically significant trend. Exposure ≥ 400 mg kg-1 to methyl paraben in soil resulted in increased abnormalities in earthworms where a normal survival-EC50 value of 397 mg kg-1 was estimated . An acute exposure to methyl paraben in soil at ≥ 60 mg kg-1 increased F. candida mortality and chronic exposure at concentrations ≥150 mg kg-1 decreased the reproductive rate . However, methyl paraben is often detected at concentrations ranging from 15.9 – 203.0 µg kg-1 in sewage sludge, levels that are well below the concentrations where toxicity was observed .The studies highlighted above suggest that CECs are ubiquitous in the environment and that exposure, even at environmentally relevant concentrations, these contaminants may be hazardous for terrestrial organisms. However, studies also suggest that these organisms can metabolize, transform and detoxify these CECs. The interplay between the toxicological effects of CEC exposure and an organism’s ability to take up and metabolize these contaminant is poorly understood and serves as significant knowledge gaps in understanding the fate and risks of CECs in terrestrial environments. These gaps must be addressed to gain better risk assessments of CECs during the use of bio-solids and treated wastewater in the agro-environment.

To address these gaps, we carried out a series of experiments utilizing plant cell cultures, hydroponic cultivations, earthworm incubations, high-resolution mass spectrometry, 14C-tracing, and enzyme assays to systematically evaluate the fate, metabolism, and biological effects of sulfamethoxazole, diazepam, naproxen, and methyl paraben and their major metabolites in terrestrial organisms under laboratory conditions. The four CECs were selected based on their detection in TWW and bio-solids, their range of physicochemical properties and uses, and the paucity of information about their fate and impacts in the literature . The study systems included Arabidopsis thaliana cells cultures, radishes, cucumbers, and E. fetida. Organisms were selected due to their extensive use in the literature, commercial availability, and worldwide agricultural relevance. Over the past two decades, pharmaceuticals and personal care products have emerged as contaminants of environmental concern due to their extensive use and continuous emission into the environment . PPCPs are released into the environment primarily through the disposal of treated wastewater and bio-solids from wastewater treatment plants . As climate change and population growth places an increasing stress on freshwater resources, especially in arid and semi-arid regions, communities have turned to utilizing municipal treated water for agricultural irrigation, which may result in soil contamination by PPCPs . Furthermore, the heavy use of some pharmaceuticals, particularly antibiotics, for disease control and growth promotion in intensive animal farming also contributes to contamination of agricultural fields when animal wastes are used for fertilization . The presence of PPCPs in irrigation water and soil can lead to contamination of food crops if plants can substantially accumulate these compounds. Various studies over the last decade have sought to quantify plant uptake of PPCPs, and in general, only low levels of PPCPs have been found in edible tissues . The majority of studies to date have only targeted the parent form of PPCPs for analysis. However, plants have a cascade of enzymes that may extensively transform xenobiotics such as PPCPs after uptake . Recently several published studies have explored the metabolism of pharmaceuticals in plants . Therefore, consideration of metabolism and biologically active metabolites is much needed for a better understanding of the fate and risks of PPCPs in the soil-plant system. Higher plants have many detoxification enzymes similar to those in animals. These enzymes function in plants as a ‘green liver’ . In general, metabolism of xenobiotics includes three phases. Phase I involves modification reactions such as oxidation, hydrolysis, and dealkylation reactions introducing reactive sites to the molecule. Phase II is characterized by conjugation with large polar bio-molecules, such as sugars and amino acids, to further increase the polarity of the xenobiotic. Phase III is typified by sequestration, resulting in the formation of bound residues . As shown for many xenobiotics in mammals and plants metabolites from phases I and II often retain biological activity , and therefore should not be discounted. In this study, sulfamethoxazole was selected as the compound of interest because of its prevalence in WWTP effluents and increasing concerns over the propagation of antibiotic resistance .

Posted on

It is our hope that this discussion serves as a figurative road map for drawing your own conclusions

Non-human actants such as soil, water, and organic certification, are not included in this diagram. Further, it only accounts for actors that were encountered during fieldwork and is not meant to be exhaustive. Instead, it hopes to provide a snapshot of the ever-changing networks of actors and actants that were involved during the research period . The practice of mapping out the flows allowed us to identify key nodes of power among the urban agriculture networks in San Diego County, which are indicated on the diagram by use of a darker hue of the parent shade used for each network. For example, Leichtag Foundation is a key node of power in the Coastal Roots Farm actor-network. These actors marshall considerable power in comparison to the other actors enrolled in the networks, whether through the possession of crucial resources such as land and capital, political power, and/or consensus-building. In what follows, we discuss the discoveries we made through examining the vignettes and the network relationships. This discussion provides the results we drew from analyzing the vignettes and the network diagram.The microgeographies of these local commodity circuits had considerable influence on the discursive and material relations present at these sites. Narratives around place drove and legitimatized sites’ growing practices and their approaches to justice, whether based on donations or democratic participation. Further, the characteristics of place drove production, distribution, and consumption practices, which had important implications for justice. Every place in this research had different needs and populations, which drove their place-specific emphases and practices. For example, a mission focused on food sovereignty might be inappropriate in an affluent,plastic plants pots primarily white community like Encinitas . However, this mission is apt in a low-income, minority neighborhood like Southeastern San Diego, which has experienced considerable disinvestment and structural oppression.

These missions at our sites were fitting and reflected what was going on in those places and within their communities. This drove not only production practices, but also distribution and consumption – the lack of substantial need in Encinitas led to distribution in “less fortunate” communities outside of the neighborhood in order to fully realize their mission. This distribution pattern resulted in a more geographically dispersed network that engaged multiple communities with disparate experiences in a single commodity circuit. The characteristics of place and the narratives around production and distribution drove the actors and actants that enrolled in these networks. The most successful and stable networks in our cases, Solutions Farms and Coastal Roots Farms, successfully enrolled actors with substantial capital resources such as Leichtag Foundation and Alliance Healthcare. Indeed, Daftary-Steel, Herrera, and Porter convincingly argue that urban agriculture projects can only truly sustain themselves and produce public goods like nutritious food, education, and job readiness with external investment in the absence of “major shifts in our national wage structure” . Three factors, we argue, contribute to this successful enrolment of funders: proximity, measurable outcomes, and narrative content. Powerful actors, especially those with sustaining capital resources, are often not located in areas of the most need like Southeastern San Diego and therefore may have few, if any, ties to the neighborhood. Measurable outcomes also play a role in enrolling actants with capital resources – as we illustrated in Chapter 3, sites that practice distributive justice, which produces more readily quantifiable outcomes, attract more funding because they can illustrate the efficacy of investment. Although Mt. Hope Community Garden is still successful at enrolling philanthropic foundations into its network, investments are relatively small because of the difficulty of quantifying outcomes like participation and social cohesion. The final aspect is the content of narratives associated with each urban agriculture site, which are part of what makes them unique places. These narratives are both produced by the actor-networks and at the same time powerful actants that shape these networks – an important contribution of Actor-Network Theory. Mainstream neoliberal and reformist narratives that focus on social enterprising and food security may be more successful at attracting funding, as opposed to narratives that focus on food sovereignty. Indeed, funders are often less connected to the histories of structural oppression that drive grassroots urban agriculture projects like Mt. Hope Community Garden. This trend results in a situation in which the most disenfranchised find it difficult to enroll actors with crucial financial resources, giving support to the hypothesis that those with significant resources are more successful at attracting funding .

It also reinforces race- and class-based inequalities because projects run by disenfranchised groups, which more often have progressive or radical agendas , struggle to obtain the support necessary to sustain themselves financially. We saw this in our analysis of Mt. Hope Community Garden. The food justice narratives that surround the garden and its parent organization do successfully enroll actors with knowledge and skills to support its activities. However, the garden received considerably less funding from its network members, leaving it at the helm of the City of San Diego and its decision to sell their property. Actants like soil, water, technology, produce, and the narratives attached to them also drive action and enroll actors into the networks supporting urban agriculture commodity circuits. For instance, the produce grown at the sites determines the extent to which the organizations can generate revenue, feed people, and drive their mission. The use of soil and narratives around its ability to foster community are particularly salient at sites like Coastal Roots Farm. Technology and narratives around innovation similarly enroll actors that value modernization and novelty – technology played an important role in Solutions Farms enrollment of Alliance Healthcare and its $1 million-dollar Innovation grant. These actants, as Bosco describes them, allow our case sites to “become what they are” and explain why some networks and the justice activities embedded within them are more sustainable than others . Tracing the many connections and relations across our commodity circuits illustrates that the story is more complicated than the presence or absence of soil. Watercress is a semi-aquatic plant that grows in f lowing shallow freshwater and is found across Europe, Asia, the Americas, the Caribbean, New Zealand and Australia. Watercress is placed within the Brassicaceae family together with several other important food crops including broccoli, kale, cabbage, and mustard. A significant amount of commercial aquatic watercress cultivation is centred in a few locations including Florida in the USA, southern Spain and Portugal, France and the south of England, with 90% of production occurring in Dorset, Hampshire and Wiltshire. These chalky areas provide nutrient-rich spring water and boreholes that directly supply the watercress beds. Phosphate-rich fertiliser is used to boost crop yield; however,blueberry pot this presents a major challenge in watercress production since it results in direct leakage of phosphate into the waterways which have high conservation value.

Excess phosphate results in eutrophication of aquatic ecosystems, a process where nutrient enrichment of water sources results in excessive algal and plant growth, and subsequent disruption of ecosystem community dynamic. Approximately 90% of watercress farms in the UK are on, or upstream of, a Site of Special Scientific Interest , increasing the pressure to minimise phosphate release.Phosphate is vital for plant survival; it forms the phosphodiester bonds that link nucleotides in nucleic acids and is critical for the structure of proteins and carbohydrate polymers, for powering cells through the release of phosphate from ATP and for regulating several metabolic pathways Symptoms of P deficiency are retarded growth, increased root:shoot biomass, decreased leaf area and often dark green or purplered colouration in severely deficient plants due to anthocyanin production. Ninety percent of the global demand for phosphorus is used for food production, however, rock phosphate is a limited resource with estimates that reserves could be exhausted in the next 50–100 years . In addition, most of the remaining rock phosphate reserves areunder the control of only a few countries, with Morocco and the Western Sahara holding over 70% of the total reserves, making it sensitive to political instability. This, combined with increasing costs of extraction and issues of eutrophication,make reducing fertiliser use an important global driver. The high reactivity and low solubility of phosphates make them commonly the growth-limiting nutrient for plants. Accounting for fertiliser application, approximately 30% of global cropland area exhibits soil P deficits although global P imbalances in water sources have not been investigated to any significant extent.Like soil, P in aquatic systems is also divided into different fractions based on solubility and reactivity in aquatic systems, with dissolved orthophosphate the most bio-available. P in water adsorbs to oxides and tightly binds with carbonates in the same manner as when in soil. However, the P inputs to natural water systems and the interaction with P in bed sediments is altered. This creates a dynamic source of phosphorus that transfers between particulate and dissolved forms, between bed sediments and the water column, and between dead and living material . In a watercress bed, the sediment is shallow gravel and thus P uptake from water likely represents the major P source. This is ref lected in a study by Cumbus and Robinson who found that a greater proportion of P was absorbed by the adventitious roots of watercress , compared to basal roots. However, some organic detritus held within the sediment should still be considered. Phosphate dynamics in hydroponic agricultural systems such as watercress beds have not been studied, representing a knowledge gap, but P is likely uniformly distributed due to f lowing water and regular maintenance of P concentrations. Since P retention in sediments is high, P delivery into freshwater systems is largely governed by release from point sources such as sewage treatment works , leaking septic tanks, and from excess fertiliser application. Globally, domestic sources contribute 54% to total P inputs into freshwater systems, 38% from agriculture and 8% from industry. Although substantial steps towards P reduction in fresh waters have been made over the last 50 years there is still much to be done, with only 40% of European surface waters currently in good ecological status.

Eutrophication of watercourses is also prevalent across the UK: in the most recent analysis, 55% of river water bodies in England failed to meet the revised P standards for good ecological status. Eutrophication is both an economic as well as environmental issue. In the US, the economic damage of eutrophication equates to $2.2 billion annually, due to losses in recreational water use, waterfront real estate, recovery of endangered species and drinking water. Naturally, phosphate levels in chalk aquifers are less than 20 μg/l, however, inputs of phosphate rapidly increase these concentrations above P targets downstream of watercress farms. In the river Itchen where several watercress farms are located, total SRP load comes predominantly from sewage treatment works but watercress beds can be responsible for up to 62% of the total reactive phosphate in some chalk streams, suggesting room for improvement in P management. Casey and Smith found watercress beds increased mean P concentrations which may cause undesirable growth of algae and disruption of community dynamics. One important strategy to tackle this problem of eutrophication is through plant breeding. By breeding watercress varieties with improved phosphorus use efficiency , the impact of watercress farming on eutrophication could be minimised. To date, no breeding for nutrient use has been conducted in watercress even though P release represents a clear issue in watercress production.Phosphate use efficiency is defined as the capacity for biomass production using the P absorbed . Here PUE is used as a broader term that also encompasses phosphate acquisition efficiency, defined as the ability to take up P, as has been used in several studies. Plant traits underpinning PUE can be observed at the macroscopic, microscopic, and molecular levels and we consider their relevance to future breeding for enhanced PUE. To date, knowledge on P acquisition by aquatic plants only covers the effectiveness of plants for phytoremediation , rather than breeding for PUE in aquatic crops such as water chestnut , water spinach , lotus and watercress. Present information does not cover morphological or genetic components to improve PUE in aquatic species, and with new plant species emerging as suggested model organisms, watercress is offered as a model crop for aquatic systems.

Posted on

The clearest distinction in this figure appeared to be whether the growing sites are for-profit or nonprofit

For instance, 75 percent of the articles returned in our Web of Science search were published after 2009 and 18 percent were published in 2017-18. A more recent search of these terms in April of 2018 returns 1622 records revealing a continued growth in literature on urban agriculture. Of these records, journal articles dominate . Other records include book reviews, article reviews, proceedings papers, and meeting abstracts. The main contributing journals included Land Use Policy , Landscape & Urban Planning , Agriculture & Human Values , Sustainability , and Local Environment ; however, the sources were quite diverse. Each record represents a single document and together they form the corpus used to build the reference topic model. Prior to processing, we removed any stop words, punctuation, and URLs. We performed LDA topic modelling using the MALLET program . We produced various topic models using three granularities , and used the models with the greatest log likelihood . We then examined their topic composition and removed topics dominated by non-meaning-bearing terms including time and location indicators and general publication information . These topics were identified using the alpha hyperparameter, where relatively high values indicated that the topic was common throughout the corpus and therefore not meaningful for examining differences within our sample. After these adjustments, we determined that the 25-topic model was ideal for analysis using personal expert knowledge on urban agriculture literature. The reference topic model was created in order to perform inference on content produced by urban agriculture growing sites and regional organizations in San Diego County – in other words, to interpret the content produced by the key actors identified above . We created a corpus including all textual content from the websites of agencies in our sample,plant pot with drainage with content from each of the 48 observations contained in a single document in the corpus.

Textual content included any written descriptions on the website including history, mission and vision statements, program descriptions, excluding locations, contact, and event info. For growing sites associated with larger organizations or institutions, we also collected basic descriptive content from the parent website. By applying the reference model to all the documents, each document is characterized in terms of topic composition, allowing comparisons among documents . The output of the inferencing process is a document-topic distribution matrix, from which we computed a matrix of cosine similarities among documents. In order to visualize these similarities, we used a dimensionality reduction technique known as multidimensional scaling . In the resulting output, each document is described as a 2-D point in Cartesian coordinates, where proximity relates to similarity. The resulting discursive map displayed the inferenced website corpus, with each point representing a single growing site or organization. The location of each point relates to its particular topic composition. The distance between points is indicative of their discursive similarity – the closer two points are in the discursive map, the more similar their topic composition; the farther apart, the more dissimilar. We investigated this map, but also created a series of variations, altering the symbology of the discursive map to reflect particular features of the sites. This allowed us to examine the connections between characteristics like growing methods and topic composition. We were also interested in discovering clusters among the data points, and so we utilized k-means clustering to identify meaningful groups in our data . K-means is a heuristic algorithm that attempts to partition aninput dataset into k groups, allowing researchers to explore clusters within a dataset. Our data seemed to occupy primarily three quadrants in the discursive map, and so we chose to identify three classes. This algorithm was run for 1,000 iterations and the results with the lowest sum of squared errors – a metric that explains the difference between each observation and its corresponding k-means centroid – were chosen as representative. This analysis complemented our visual analysis of symbology patterns. The growing methods symbology illustrating the practices used by growing sites revealed a distinct, but blurry pattern between motivation and practice.

When analyzing the map using this symbology, a general pattern emerged in which technologically-advanced sites tended to group in the top-left quadrant of the map with two outliers: Go Green Agriculture and Archi’s Acres. The absence of innovation in these outliers’ top-three loadings suggested that other topics precede technology in how these growing sites describe themselves despite their use of advanced technologies. Generally, soil-based sites occupied the right side of the discursive map; however, soil-based farms such as Suzie’s Farm, Good Taste Farm, and Point Loma Farms were grouped in with the soilless sites. Growing site and organization descriptions of their processes did drive their location on the discursive map. For instance, the soilless sites often described the inventive and underrepresented practices they use to grow produce in the urban environment. However, the content did not end there. Other topics like social movements, climate change, and food access were also present among these sites. We saw a similar trend with sites using a community gardening model. When we explored the entire topic loadings of growing sites and organizations, ignoring practice-based topics like innovation and community gardening topics, we saw that the clusters have far more similarities than differences. Interestingly, these soilless sites are typically affiliated with businesses as opposed to nonprofits which dominate the right side of the map, where most soil-based sites are located . Indeed, we expected that business and nonprofit website content would vary and these results provide evidence to that effect. San Diego Food System Alliance, the leading regional nonprofit organization, is located in the center of the map. This location is not surprising in the context of neoliberal governance in which cities and regional organizations are more focused on building consensus and supporting apolitical agendas, rather than taking on political causes .The affiliation symbology illustrating the relationship between institutional affiliation and content was less coherent than the other symbologies displayed in previous figures, but still offered important insights. Growing sites were affiliated with a variety of institutions including schools, churches, organizations hosting training and educational programs, and for-profit businesses.

Education sites were located throughout the map suggesting that training and skill-building are not major dividing factors in discourse. In other words, many different types of organizations claim to focus on education. However, church, community, and school gardens tended to concentrate in the top-right section of the map, which is typically associated with soil-based community gardens. However, it cannot be assumed that the for-profit sites lack social mission. For example, Archi’s Acres, a for-profit hydroponic farm in Escondido, includes a social enterprise function focusing on training veterans in hydroponic farming. Sundial Farms, a veteran- and immigrant-owned, hydroponic farm in the Innovation cluster, is a direct result of this program. This social function features prominently in its website content: “At Archi’s, we believe a key aspect of successful business is how it meets its responsibility to the community in which it operates and the customers which make up its marketplace. We do this by integrating into our business model an opportunity to support others including our military service members and veterans.” This broader social mission may explain its topic loadings and the absence of innovation as a primary topic. The overall uniqueness of this growing site may explain its peripheral location in the discursive map. Solutions Farms, an aquaponic operation associated with Solutions for Change,growing blueberries in pots was the only nonprofit located in the for-profit dominated section of the map. The organization aims to alleviate family homelessness in the county through skill development, including training in aquaponic farming. However, innovation is the primary topic in their content, influencing their location among other sites whose discourse is focused on innovation.Multivariate clustering was performed on the discursive map to identify clusters in the sites and group them accordingly. Figure 8 contains the k-means results including three classes . Transitional sites were identified by creating a 4-class result . The topic compositions of sites in each cluster were examined and the clusters were given descriptive names reflecting their dominant topics : Innovation, Community, and Access. The transitional sites – those that broke off into their own group in the 4-class result – were signified using an overlaid line pattern. These sites were close to or straddled the center axes of the map.The Innovation cluster was distinct from the other clusters. The predominant topic amongst this group was innovation, which includes words and phrases like rooftop farming, zero-acreage farming, soilless, aquaponics, buildings, hydroponic, vertical, greenhouses, indoor, and technology as well as production, yield, growth, and quality. Unsurprisingly, all of the technologically-advanced sites resided in this cluster with the exception of Valley View Farms, which experiments with hydroponics, but focuses primarily on animal farming. Among the topic loadings in this group were community gardening, food access, social movements, climate change, water management, food production, and food security. This cluster also consisted primarily of for-profit growing sites with the exception of Roger’s Community Garden located on the University of California, San Diego campus. An interesting outlier is Go Green Agriculture, a hydroponic farm, which is located on the border of the Community cluster. This location is likely driven by its top topics, which include community gardening, location, and climate change, which are well-represented in both the Innovation and Community cluster. The Community cluster emphasized connections with local residents, primarily promoting home and community gardening – community gardening was the most prevalent topic in this cluster.

Although, this cluster overlaped considerably with the Access cluster, there was a clear emphasis on environmental topics including ecosystem conservation, water management, location, water contamination, innovation, and climate change. The social movement topic was also prevalent throughout this cluster with many of its sites expressing a dedication to alternative forms of organization. It is also worth noting that the socio-economic characteristics of the two neighborhoods are also quite different. Southeastern San Diego, specifically zip-code 92102 where Mt. Hope Community Garden is located, is a primarily Hispanic community, followed by White , African American , and Asian . The median income is at $42,464 with only 24 percent of the population exceeding $75,000 annually . The sites and organizations in this cluster also placed considerably less emphasis on environmental topics in favor of more social topics including public health, food production, and urban greening. Still, topics like ecology and climate change were present suggesting that environmental and social concerns were not mutually exclusive. The sites in the Access cluster were also predominantly affiliated with educational and training programs. Two particularly interesting examples are UrbanLife Farms and Second Chance Youth Garden. Both growing sites are wings of social justice organizations that offer job training and skills development for youth living in City Heights and Southeastern San Diego – communities that have seen considerable disinvestment and suffer from high unemployment . Other growing sites like Rolling Hills Grammar School and Literacy Garden and Olivewood Gardens and Learning Center also focus on youth programming. Not all the growing sites in this cluster work with youth. New Roots Farm concentrates on providing resettled refugees with land for farming, small-business training, and nutrition education to help them adjust to a new life away from their home country. This mission guided its topic loading of food security, social movements, and food access. The five urban agriculture supporting organizations we surveyed spanned the Community and Access clusters. Slow Food San Diego, Slow Food Urban San Diego, San Diego Roots Sustainable Food Project , and San Diego Community Garden Network are located in the Community cluster. San Diego Food System Alliance was located at the border between the Community and Access clusters suggesting that food access was a more prominent topic for the organization. Further, its central position illustrated the consensus focus of the organization, which caters to a diverse group of actors including politicians, businesses, and nonprofit organizations. Overall, the placement of the organizations made sense as they are nonprofit facilitators for other sites aimed at broader social goals like increasing food access and building community.

Posted on

Cereals are inherently low in protein and mineral micro-nutrients such as Fe and Zn

When necessary, data was transformed using power transformations to satisfy ANOVA assumptions. Hydroponic experiments were performed in growth chambers at 22-23 °C with a photoperiod of 16 h light / 8 h dark provided by fluorescent lights supplemented with incandescent lighting. In all experiments, grains were imbibed at 4°C for four days, after which they were placed at room temperature. Once most of the grains had germinated and the coleoptiles had emerged, healthy seedlings were transferred to a mesh suspended on water or CaCl2 . Four days later, healthy seedlings were transferred to tanks with growth solutions 6Mo7O24.4H2O 0.05 M, CuSO4.5H2O 0.5 M, ZnSO4.7H2O 1 M, MnSO4.H2O 1 M, FeEDTA 0.1 mM, Ca2 1.0 mM, 2SO4 1.0 mM. After removing the grain, seedlings were wrapped at the crown with foam and inserted in holes pre-cut in a foam core board placed on top of the solution. Nutrient solution was changed two to three times a week for the duration of the experiment. Particular details of the methods used in the two laboratories are described below: Davis, CA, USA: The experiments were performed in 13 L hydroponic tanks containing the nutrient solution. Twenty-four seedlings were placed in each tank in a six by four pattern. All genotypes were included in one tank and, if necessary, multiple tanks were used as replications. In the experiments to study the effect of different nitrogen sources and concentrations , seedlings were grown in normal growth solution for seven days and then transferred to four separate tanks with each of the four nitrogen sources for 10 days . Roots were measured at 22 DAG. Each tank included 6 replications of each of the four genotypes organized in a completely randomized design. The results were analyzed in a 2 x 2 factorial ANOVA with distal and proximal 1RS regions as factors and wheat or rye chromosome segments as levels. For the analysis of distances between the first lateral roots and the RAM, round plastic planter the four genotypes were grown in a tank with normal nitrogen conditions in a completely randomized design . Lines carrying distal rye or wheat segments were compared using a t-test. Chascomús, Buenos Aires Argentina: The CaCl2 from the germination tank was replaced by nutrient solution on the 4th day. On the 5 th day, plants were transferred to 350 mL pots containing nutrient solution, with each pot being a replicate.

Pots were rotated every two days to ensure that they occupied different positions within the growth chamber. For the root elongation time course, the length of the second longest seminal root was measured daily four hours after the start of the light period, starting 6 DAG. Within each experiment, data was analyzed as repeated measures . A combined ANOVA was performed using experiments as blocks. Previous studies have shown an association between the introgression of the rye 1RS arm in wheat and improved resistance to water stress . In three of these studies, the 1RS.1BL lines showed increased root biomass compared to the non-1RS control lines in large pot or sand-tube experiments. However, these differences were not validated in the field. In this study we showed that differences in grain yield and biomass between plants carrying a complete 1RS translocation and NILs with an introgressed distal wheat chromosome segment are associated with differences in total root length density and average root diameter in the field. Field excavations of the four different 1RS NILs provided an opportunity to visualize the differences in their root systems and to quantify these differences using horizontal soil cores at consistent depths. This experiment confirmed the hypothesis that the 1RSxR lines have a higher root density throughout the soil profile, with roots that reach deeper in the soil than the 1RSxW lines . The more extensive root system of the 1RSxR lines relative to the 1RSxW lines may have contributed to their better tolerance to drought and water logging conditions in the experiments presented in this study , and to the higher carbon isotope discrimination and increased stomatal conductance values detected in a previous study . Through their deeper root system, the 1RSxR plants can access more stored soil moisture and nutrients, keep their stomata open longer, and generate additional photosynthetic products and biomass than the 1RSxW plants. However, we cannot rule out the possibility that the genes in the distal 1BS introgression may have a more direct effect on aerial biomass or on other anatomical and/or physiological root differences known to impact tolerance to water logging and drought .

The differences in root depth observed between the Hahn 1RSxR and 1RSxW NILs in the field were paralleled by drastic changes in seminal root length in hydroponic cultures . These differences were robust across experiments and were detected with different nitrogen sources and concentrations . We hypothesize that these early differences in seminal root length may have contributed to the observed differences in total root length density observed in the deepest soil core samples in the field . The early and consistent differences in root growth under controlled conditions provided the opportunity to study the process in detail. During the first week of development, root growth occurred at the same rate for both genotypes, suggesting that the differences were not primarily associated with embryonically determined differences in root elongation. Instead, differences in root growth consistently manifested during the second week across multiple experiments. The growth rate of the seminal roots of the 1RSxW plants gradually decreased during the second and third week, to come close to zero by the end of the third week, whereas growth continued in the 1RSxR plants . The consistent timing of these events suggests that these changes are developmentally regulated. The growth arrest of the seminal roots in the 1RSxW plants was accompanied by the proliferation of lateral roots in close proximity to the RAM, suggesting important changes in the RAM. The RAM consists of a quiescent center surrounded by stem cells that generate new daughter cells, which undergo additional divisions in the proximal region of the meristem and differentiatein the transition zone . At a cellular level, a balance between cell proliferation and cell elongation/differentiation determines root growth rate . The arrest of the growth of seminal roots in 1RSxW plants suggests a modification in cell proliferation and/or cell elongation/differentiation. Additional studies will be required to determine if this arrest involves changes in the QC and/or modifications in the root regions adjacent to the meristem. In any case, the dramatic reduction in seminal root growth and increased lateral root proliferation close to the RAM argues for an early developmental program switch in the regulation of the RAM in the 1RSxW plants.

The transition from cell proliferation to cell elongation and differentiation and the subsequent development of lateral roots depends on the distribution of ROS along the root axis, specifically on the opposing gradients of superoxide and hydrogen peroxide. Superoxide is predominant in dividing cells in the meristematic zone, while hydrogen peroxide is predominant in elongated cells in the differentiation zone . The balance between these ROS modulates the transition between root proliferation and differentiation zones. Seventeen days after germination,round plastic plant pot the apical region of 1RS seminal roots showed opposing gradients of superoxide and hydrogen peroxide characteristic of elongating roots . A different ROS distribution was detected in the arrested 1RSxW roots, where superoxide was restricted to the distal ~700 m and increased levels of DCF-DA fluorescence were detected between 250-950 m in the cell proliferation zone . The contrasting patterns of ROS distribution reflect the major developmental changes that differentiate the seminal roots of the 1RS and 1RSxW genotypes. Studies in Arabidopsis have shown that changes in ROS distribution can be triggered by the altered expression of major genes that control the size of the meristematic zone. These genes include UPBEAT1 , a basic helix-loop-helix transcription factor that regulates the meristematic zone size by restricting H2O2 distribution in the elongation zone . In addition, ROOT MERISTEM GROWTH FACTOR 1and the transcription factor RGF1 INDUCIBLE TRANSCRIPTION FACTOR 1that mediates RGF1 signaling can modulate the distribution of ROS along the root developmental zones leading to enhanced stability of PLETHORA2 . Reduced expression of PLETHORA in the root apical region or changes in its distribution have been associated with impaired root growth. To test if these Arabidopsis results are applicable to wheat, we are initiating expression studies of these genes in the 1RSxR and 1RSxW lines. It remains unknown if the differential pattern of ROS distribution in the roots of the 1RSxW plants is the result of changes in the wheat homologs of these central developmental genes or a more direct effect on genes affecting the redox balance in different developmental root zones. The differences in superoxide and hydrogen peroxide distribution between the seminal roots of the 1RSRW and 1RS plants were measured after the arrest in root growth . Therefore, we currently do not know if the changes in ROS distribution are a cause or consequence of the changes observed in root growth and lateral root proliferation close to the RAM. Wheat is a crop of major importance and together with other staple cereals supply the bulk of calories and nutrients in the diets of a large proportion of the world population . A major focus of wheat breeders has been grain protein concentration as it affects bread- and pasta-making quality, but micro-nutrient improvement has received less attention. Approximately half of the world’s population suffers from Fe and/or Zn deficiencies and millions of children suffer from protein-energy malnutrition . As such, the improvement of nutritional quality of wheat could benefit the nutritional status of millions of people. A common agronomic practice to increase grain protein concentration is the use of N fertilization. However, this practice is expensive and excess fertilizer run-off is a potential environmental contaminant .

A substantial percentage of the N in wheat grain is supplied by amino acids remobilized from vegetative tissue . Much of this N content is derived from proteins that are disassembled and recycled during the leaf senescence stage of development . Likewise, Fe and Zn have been shown to be remobilized from vegetative tissues in several plants , although the specific sources are unknown. Zinc fertilization has been a successful strategy to improve wheat grain Zn concentration , and improvement in the partitioning or remobilization of Zn to grain could make fertilization efforts more efficient. Wheat grain with higher Zn concentration has been demonstrated to produce more vigorous crops . Thus, breeding or transgenic approaches that result in plants with increased partitioning of minerals to grain could be useful for both nutritional bio-fortification and reduced fertilizer application. Chromosome 6B from wild emmer wheat was identified as a potential source of genetic variation for grain protein , Zn, and Fe concentration . A quantitative trait locus for grain protein concentration was mapped on chromosome arm 6BS and later mapped as a single Mendelian locus, Gpc-B1 . In near-isogenic lines of this locus, increased grain protein was associated with the increased remobilization of amino acids from the flag leaf , higher grain Fe and Zn concentrations , and accelerated leaf yellowing, indicating accelerated senescence . A NAC transcription factor, NAM-B1, was identified as the causal gene for Gpc-B1 by positional cloning . Other members of the NAC family are known to regulate developmental processes , including leaf senescence . In transgenic wheat NAM RNA interference lines in which NAM-B1 and its homeologous genes had decreased expression, leaf yellowing was delayed, and grain protein, Fe, and Zn concentrations were greatly decreased . These results, together with higher N, Fe, and Zn concentrations in RNAi line flag leaves at maturity, suggested a role for NAM-B1 homeologues in the remobilization of N compounds, Fe, and Zn. However, without taking organ mass, nutrient concentrations at prior time points, and total nutrient accumulation of other organs into account, this model could not be confirmed. In addition, the body of literature does not contain sufficient data regarding sources of grain minerals to support the idea that remobilization alone could account for the differences observed. Because a whole-plant partitioning profile has not been undertaken in plants differing in NAM-B1 expression, it is currently unclear whether this gene directly affects remobilization , alters partitioning of nutrients within the plant, alters total plant uptake of these nutrients, or influences a combination of these processes.

Posted on

Human norovirus is one of the major causes of acute gastroenteritis worldwide

Elevated temperatures cause an increase in transpiration as the plant’s mechanism to decrease leaf temperature . However, prolonged transpiration and dry soil conditions may alter a plant’s strategy to mitigate heat stress due to the need to conserve water. Considering that we saw an increase in ABA content with increased CEC concentrations, we speculated that the cucumber plant’s ability to adapt and mitigate heat stress would be further impaired due to exposure to CECs. The ABA content in cucumber tissues followed the same general trend under heat stress conditions as it did under non-heat stressed conditions . No differences in root ABA content due to heat stress were observed within the treatments, however the 1X and 20X CEC treatment with heat stress were significantly decreased from the control with heat stress . Similarly, significant differences in leaf ABA content due to heat stress were not observed within the same CEC treatment, but did show a consistent elevated trend across the range of CEC treatment levels when the plant was also subjected to heat stress. It must be noted that only a 4 d heat stress with somewhat moderate, but realistic, temperature regimes was examined in this study. If this observed trend were to continue, it could have a significant effect over the long-term health and development of the plant. It is possible that prolonged exposure to heat stress and the resulting increase in abscisic acid content and anti-transpiration activity could ultimately affect biomass production and water use efficiency.The virus is a leading cause of food borne illness in the United States,25 liter pot causing nearly 58% of foodb orne disease . Fresh produce has been identified as a leading cause of food borne illness and is a major high risk food associated with human NoV outbreaks in the US . Vegetable row crops and fruits were responsible for 30% and 21%, respectively, of human NoV food borne outbreaks in the US .

Vegetables and crops can be contaminated with human NoV at any point from farm to fork. Evidence has shown that the source of pre-harvest contamination mainly comes from soil, fertilizer, or irrigation water. Though human NoV is a major contributor to fresh produce associated outbreaks, the modes of contamination and persistence of the virus in vegetables remains poorly understood. Human NoV is a non-enveloped single stranded positive sense RNA virus of the family Caliciviridae . The major challenge in human NoV research is that currently there is no robust cell culture system for the virus. Recently, two cell culture systems were developed for human NoV, but have not yet been optimized to produce high viral titers . Therefore, much of the understanding of human NoV molecular biology, pathogenesis, and environmental stability has come from the study of surrogate viruses . Many viruses within the family Caliciviridae have been utilized as human NoV surrogates, including murine norovirus , feline calicivirus , and Tulane virus . Tulane virus is a newly recognized surrogate for human NoV and is member of the genus Recovirus within Caliciviridae . TV was shown to have similar pH stability to human NoV and other surrogates at ranges from pH 3 to pH 8 . TV causes enteric infection in primates and also recognizes histo-blood group antigens as a cellular attachment receptor, similar to human NoV . Internalization of pathogens in growing produce is considered one of the potential routes for contamination of fresh produce . Bacterial pathogens, such as Salmonella enterica serovar Typhimurium and Esherichia coli O157:H7, have been shown to be internalized in vegetables including lettuce, radishes, alfalfa and green onions . Human NoV has also been shown to be internalized in growing produce such as lettuce, spinach, and green onion . However, few studies exist where multiple types of produce have been evaluated for viral internalization in parallel. In addition, the influence of initial inoculum levels on viral internalization in different types of produce has not been evaluated extensively.

In this study, green onion, radishes, and Romaine lettuce were selected to evaluate the effect of growth matrix, inoculum level, and vegetable type on the internalization of human NoV and TV in fresh produce. Human NoV GII.4 strain 707 was originally isolated from an outbreak of acute gastroenteritis in Ohio. The virus genomic RNA was quantified by reverse transcriptase quantitative PCR and then stored at −80 °C. TV was generously provided by Xi Jiang at Cincinnati Children’s Hospital. TV was propagated in confluent monolayers of the monkey kidney cell line MK2-LLC . MK2-LLC cells were cultured at 37 °C in a 5% CO2 atmosphere in low serum Eagle’s minimum essential medium supplemented with 2% FBS. Before virus infection, MK2-LLC cells were washed with Hanks’ balanced salt solution and subsequently infected with TV at an MOI of 1. After 1 h of incubation at 37 °C, 18 ml of Opti-MEM with 2% FBS was added. The virus was harvested 2 days post infection by three freeze thaw cycles followed by centrifugation at 3000 × g for 10 min to remove cell debris. After centrifugation, the supernatant was collected and virus stocks were stored at −80 °C. TV titer was determined by plaque assay. Seeds of green onion and radish were purchased from Livingston Seed and stored at 4 °C. Before sowing, the seeds were soaked for 1 day at room temperature in a 500 ml beaker of tap water. Subsequently, the water was drained and the seeds were covered with 2 layers of wet Kim wipes for 2 days to accelerate seed germination. After germination, the seeds were planted in 4 inch plastic pots and grown in plant growth chamber under long day conditions in Metro-Mix® 300 soil . Two month old green onions and Romaine lettuce and one month old radishes were used for experiments. For growth in the hydroponic system, plants were removed from soil and roots were washed thoroughly with tap water to remove soil and then placed in racks above feed water. Feed water was aerated using a pump and antibiotics were added to limit microbial growth. The feed water was not replaced during the study period.

After viral inoculation, only the roots contacted the feed water and a plastic barrier separated the aerial plant tissues and feed water to limit cross contamination. For green onion grown hydroponically, TV was diluted in feed water to result in a high titer and low titer virus concentration in the feed water. Human NoV was diluted in the feed water of hydroponically growing green onions to achieve 1.0 × 105 RNA copy/ml. For hydroponically grown radishes, only the high concentration of TV was tested. For each treatment group, a 10 ml sample feed water was collected before plants were inserted and was used a control to determine the stability of TV in feed water without plants. In addition, uninoculated control groups were set up for each treatment group. The total volume of the hydroponic feed water following virus dilution was 400 ml and the initial virus titer was determined using plaque assay or RT-qPCR . Negative control plants were kept in separate tanks and no virus was added. At days 0 , 1, 3, 7, and 14, four plants were harvested for each condition and a sample of the feed water was collected. To minimize cross contamination, the upper most leaves were harvested first, followed by shoots, and roots were harvested last . Harvested tissues were placed in individual sterile plastic bags and each tissue was weighed. Next,25 liter plant pot the surface of each tissue was decontaminated by submersion in 1000 ppm chlorine followed by rinsing with water and inactivation of residual chlorine with 0.25 M sodium thiosulfate. Samples were then homogenized by grinding with mortars and pestles with 5 ml PBS . Sample homogenates were transferred to 15 ml tubes and centrifuged at 3000 × g for 10 min to remove cellular debris and the virus-containing supernatant was then transferred to a new collection tube. No virus concentration step was performed prior to detection. Detection of viruses in plant tissue samples and feed water samples was determined by RT-qPCR and plaque assay . The detection limit for RT-qPCR was determined to be 5 RNA copy/ml using dilution of plasmid standard in each sample matrix. The detection limit for plaque assay was determined to be 10 PFU/ml by diluting TV stock in each sample matrix. Three technical replicates were executed during RT-qPCR analysis and two technical replicates were used for plaque assay for each sample. The consumption of fresh fruits and vegetables continues to increase in many countries and fresh produce is an important vehicle for food borne disease transmission. The outbreaks associated with fresh produce have resulted in considerable public health and economic burdens .

Among the pathogens associated with fresh produce outbreaks, an increased incidence of infections and outbreaks are attributed to food borne viruses, most notably human NoV . It has been demonstrated that various types of plants are susceptible to internalization of human viral pathogens during growth . Various factors have the potential to affect the ability of human pathogens to internalize in growing plants including the growth substrate , plant developmental stage, pathogen type, inoculum level, plant species and cultivar, abiotic and biotic stresses . In this study, different plants types, inoculum levels, and growth matrices were tested to determine their effect on the internalization and dissemination of human NoV. Previous research has shown that the level of pathogen inoculum used to contaminate plants can greatly influence the rate of bacterial internalization and dissemination . For example, in Arabidoposis thaliana, low inoculum levels of Salmonella Typhimurium were able to colonize the root surface but did not invade the lateral root junctions. When the inoculum level was increased to 106 CFU/mL, the bacteria were able to internalize into the root . In this study, two different levels of TV inoculum, high and low , were used to contaminate the feed water of hydroponically growing green onions. TV was detected in roots of green onions in both the high and low inoculum groups. The high inoculum group had infectious virus detected in the aerial portions of the plant while no virus was detected in these tissues when a low virus inoculum was applied. Unlike bacteria that have the ability to replicate in the phyllosphere, viruses are unable to replicate outside of their host cell. However, in general it would be expected that higher inoculum levels would result in higher levels of internalization . This was the conclusion made in another study in which higher inoculums of E. coli O157:H7 in spinach showed higher contamination incidences . In another study, the internalization of Salmonella Typhimurium was highly dependent on the concentration of the pathogen present in irrigation water. Irrigation water containing 5 Log CFU/mL Salmonella Typhimurium resulted in limited incidence of internalization in lettuce, while 8 Log CFU/mL Salmonella Typhimurium in the irrigation water, significantly increased the internalization frequency. Similar to these studies, we found that increased TV contamination levels in green onions lead to increased internalization of the virus in hydroponically grown green onion. In addition, we evaluated the internalization of human NoV in hydroponically growing green onion. We found that high levels of human NoV RNA were detected in all harvested green onion tissues starting on day 1 post inoculation. The levels of RNA decreased over the study period; however RNA was still detectable in all tissues on day 14 post inoculation. The data indicates that human NoV internalized via the root of the green onions and transports to the leaves. We also used RT-qPCR to evaluate the level of internalized TV RNA in this study. We found that high levels of TV RNA were detected starting on day 1 post inoculation and that the level of RNA remained at this level at all subsequent time points. However, this differs from the internalization results obtained for TV using plaque assay as the method of detection, in which lower levels of internalization were detected and there were reductions in the level of virus internalized at later time points. This could be due to the fact that RT-qPCR is more sensitive than plaque assay and that RNA detection alone may not accurately reflect the recovery of infectious viruses in these samples.

Posted on

Nitrate-supplied plants accumulated the greatest amounts of nutrients at ambient CO2

The shoot biomass data suggest that growth differences measured early in the lifespan of wheat supplied with NH4 + or NO− 3 or NH4 + do not necessarily carry through to senescence. This may be due in part to a shift in NO− 3 assimilation to the root , allowing NO− 3 -supplied plants to compensate for the decrease in shoot NO− 3 assimilation that occurs at elevated atmospheric CO2 concentrations . The decrease in yield and biomass measures at elevated CO2 concentrations does not agree with field observations where wheat yields as well as overall biomass increased with elevated CO2 . Similarly, our results that the greatest values for other yield measures occurred at ambient CO2 concentrations varies from the literature. High CO2 has been found to increase flowering tillers , KN , and kernel mass . Conflicting results, however, have also been reported . Many of the field and open top chamber studies were grown under natural light and thus received substantially greater photosynthetic flux density than our chamber-grown plants. These higher light conditions would be more favorable to biomass accumulation. Also, these studies typically applied high amounts of mixed N fertilizer , and yields and biomass have been found to be greater under mixed N nutrition than under either NH4 + or NO− 3 alone . Finally, the wheat cultivar we used is a short-statured variety that has rarely been used in other studies and may have accounted for some of the differences between our study and other published data. Our results that NH4 + -supplied plants had greater yield and yield components than NO− 3 -supplied plants at ambient CO2 have been observed previously . Wang and Below observed greater numbers of kernels head−1 and KN in plants supplied NO− 3 that was not observed here. Their study, however, supplied NH4 + at relatively high levels . Several studies have found that incipient NH4 + toxicity can start appearing at N levels as low as 0.08–0.2 mM NH4 + ,vertical farming equipments although the onset of NH4 + toxicity depends on light level and solution pH . The poorer performance of the NH4 + treatment in Wang and Below , therefore, might derive from NH4 + toxicity.

We have previously determined that the 0.2 mM NH4 + -supplied to our plants to be sufficiently high for normal growth, but low enough to avoid toxicity problems under our experimental conditions . Our second hypothesis, that nutrient concentrations are differentially affected by the inorganic N form supplied to the plants and CO2 enrichment, was supported by our data. CO2 concentration and N form interactions may alter tissue demands for nutrients. For many nutrients, ratios between different elements are typically maintained within a narrow range . CO2 concentration and N form may disturb the balance between different nutrients, leading to a cascade of changes in demand, accumulation, and allocation among the different plant tissues .Some portion of the greater response of NH4 + -supplied plants to CO2 derived from a dilution effect from the greater biomass at ambient CO2 concentrations . Total amounts of nutrients tended to decline with CO2 enrichment for NH4 + -supplied plants, which had the greatest amounts of macro/micro-nutrients at sub-ambient CO2 . These results have not been observed in other published studies . Growth chamber studies, however, tend to have more exaggerated differences among treatments than field and greenhouse experiments , and N source cannot be well-controlled in field and greenhouse experiments. The observed increase in NO− 3 −N concentration with CO2 concentration in NO− 3 -supplied plants has been reported previously , and adds further support to the hypothesis that elevated CO2 concentrations and the resulting decrease in photo respiration inhibit shoot NO− 3 photo assimilation. Nevertheless, tissue NO− 3 − N concentrations observed here were substantially lower than those in the earlier study . Again, this may derive from difference in life stages in the two studies. Most of the N available to the plant for grain filling comes from N translocation rather than uptake from the substrate . Probably, the plants continued to assimilate plant NO− 3 using a non-photo respiratory dependent process such as root assimilation after root N uptake slowed or stopped. Loss of NO− 3 through root efflux to the nutrient solution also may have contributed to the lower concentration of NO− 3 − N.

The partitioning and accumulation of all mineral elements was affected in some manner by the CO2 treatment and N form supplied to the plants. Observations that cation concentrations decrease under NH4 + supply relative to NO− 3 supply were not apparent in this study. Again, this could be partly due to the relatively low concentration of NH4 + -supplied in our study, the age of the plants at harvest, and differences among wheat cultivars. Allocation of nutrients within the plant followed similar trends for both N forms, with the exceptions of Mn and Cu . Interestingly, in NO− 3 -supplied plants, shoot Mn concentrations increased slightly with CO2, and these plants allocated far more Mn to the shoots than NH4 + -supplied plants at all CO2 concentrations. Manganese has been found to activate Rubisco in place of Mg2+ and the Rubisco-Mn complex has been observed to decrease Rubisco carboxylase activity while minimally affecting or even enhancing oxygenase activity . The slight increase in shoot Mn with CO2 corresponded to a large 23% decrease in Mg concentration. Manganese, which can act as a cofactor for glutamine synthetase , was also the only nutrient that NH4 + -supplied plants allocated a greater percentage to the roots at the expense of the shoots. NO− 3 – supplied plants typically allocated a higher percentage of most nutrients to the roots, as has been reported previously . Phytate, which forms complexes with divalent cations, has been found to hinder human Zn and Fe absorption during digestion and thus has been labeled an “anti-nutrient.” It may serve a number of valuable functions, however, including roles as an anti-oxidant and anti-cancer agent . Phytate is also the major repository of grain P, and variation in P supply to the developing seed is the major determinant of net seed phytate accumulation . To our knowledge, no published studies have explicitly looked at how phytate is affected by CO2 concentration. Elevated CO2 has been found to have a much larger negative impact on Zn and Fe concentrations than on P in wheat .

Several studies have observed that P increases slightly with CO2 concentration, and because the majority of P is tied up in phytate, this may cause increases in grain phytate concentrations as atmospheric CO2 rises. As a result, bio-available Zn and Fe–Zn and Fe not bound to phytate – is expected to decrease even further . Nonetheless, we did not observe such trends in macro- and micro-nutrient concentrations in this study. The mechanism behind these contrasting results is not clear, although the environmental conditions and nutrient solution in which the plants were grown likely had some role. The modeled data demonstrated only a small negative impact of CO2 concentration on bio-available Zn concentrations , which was unexpected. Indeed, the grain from NO− 3 -supplied plants actually showed a slight increase in bio-available Zn between ambient and elevated CO2. These results combined with the differences in grain bio-available Zn between NH4 + and NO− 3 -supplied plants demonstrates that N form may differentially affect the nutritional status of this important nutrient, especially in less developed countries that might be more dependent on phytate-rich grains for their Zn nutrition . The milling process removes some, if not most, of the phytate and grain mineral content with the bran fraction of the grain . Regardless, with over 50% of the human population suffering from Zn deficiencies, even small increases in bio-available Zn would be beneficial . This modeling exercise, however, is not a prediction of how increasing CO2 will affect wheat nutrition so much as illustrates that N source may mediate, to some extent, the effects of CO2 on phytate and bio-available Zn, and that N source will become an even more important agricultural consideration in the future. In summary, both CO2 concentration and N form strongly affect biomass and yield in hydroponically grown wheat, as well as nutrient concentrations in above- and below ground tissues. Interactions among plant nutrient concentrations,CO2 concentrations,vertical grow system and N form are complex and non-linear. The impact of N form and CO2 concentration on the mechanisms affecting nutrient accumulation and distribution requires further research and extension to more realistic and agriculturally relevant growing conditions found in greenhouse and field studies. Of course, in greenhouse and field studies, control of N source is limited and control of atmospheric CO2 concentration is expensive. The effects of CO2 and N form on agriculture and human nutrition observed here are interesting and suggest a new area of research on mitigating the effects of climate change on agriculture. The supply of fertilizers or addition of nitrification inhibitors that increase the amount of available NH4 + may have beneficial effects for human nutrition, particularly in regards to micro-nutrient deficiencies such as Zn and Fe that currently affect billions of people worldwide. In the face of the potentially negative consequences of climate change on agriculture, all avenues of mitigation must be examined, and even small improvements may prove worthwhile.Features of the seven-story Paharpur Business Center and Software Technology Incubator Park in New Delhi India have been described. A notable feature of the building is the stated goal of providing a healthy work environment for building occupants with specific interest in maintaining superior indoor air quality.

To achieve this goal, the building utilizes several innovative air cleaning technologies, such as air washing to remove the more polar volatile contaminants, bio-filtration of building makeup air using an enclosed rooftop greenhouse with a high density of potted plants, passive treatment of indoor air using a large number of potted plants distributed throughout the building, dedicated secondary heating, ventilation and air conditioning air handling units on each floor with re-circulating high efficiency filtration and ultraviolet light treatment of heat exchanger coils, and air exhaust via the restrooms located on each floor. The idea of using potted plants to remove VOCs from the indoor environment was originally introduced by Wolverton et.al.. In addition to treating the air, the PBC management recognizes the importance of reducing potential sources of indoor chemicals by providing environmentally friendly cleaning products exclusively for the building and selecting certain materials during renovations including a combination of stone, tile and ‘zero VOC’ floor covering and solid sawn wood materials for trim, paneling and furniture, with minimal use of composite wood products. A recent short-term field study collected indoor air quality measurements at the PBC to investigate the performance of the bio-filtration air cleaning system. The study focused primarily on VOCs and aldehydes and collected measurements at several locations in the building representing the transfer pathway of air moving through the building starting on the roof outdoors and following through the rooftop greenhouse, indoors on two floors, and at the building exhaust locations. The study found that for most contaminants, the levels of common indoor VOCs and aldehydes generally increased as the air moved through the building, indicating the presence of indoor sources. The study concluded that even with the extensive effort given to maintaining superior IAQ, the building still had concentrations of VOCs and carbonyls similar to that found in other office buildings. However, the authors point out that given the outdoor air quality in New Delhi compared to the outdoor air quality where the comparative IAQ studies have been carried out for other office buildings, the findings of the short-term study may indicate some added benefit of the bio-filtration-based air cleaning technology. The increase in concentration for several VOCs and carbonyls as the air moved through the building indicated the presence of an indoor source for these chemicals. The contribution of indoor chemicals from different building materials and building contents have been investigated for a range of building types and typical concentrations measured in these buildings have been summarized. The purpose of this project was to investigate the potential source of VOCs and carbonyls in the PBC.

Posted on

Containers with plants grown in non-spiked nutrient solution were included as blank controls

All plant treatments were created in quadruplicate and solution treatments were created in triplicate. Laboratory blanks were included with each sample extraction and pure methanol was analyzed in each UPLC/MS/MS run to check potential contamination. Surrogates were used in all sample analyses to account for losses during extraction and matrix effects during instrumental analysis. Recovery of the surrogates was used to calculate the actual concentration of each target analyte. Recoveries of surrogates in plant tissue and nutrient solution samples are listed in Table S5.1 of the Supporting Information. Statistical analysis of data including ANOVA with Tukey’s Honestly Significant Difference, linear regression, and t-test was performed using R . Significance was assigned at p ≤ 0.05. Carrot, lettuce, and tomato plants grown in both environments were found to be generally healthy, and no difference in biomass was detected between plants grown in solution with or without PPCP/EDCs. For the same plant species, those from the warm-dry environment generally had greater bio-masses. One tomato plant from the cool-humid treatment had yellow, stunted leaves and was excluded from the analysis. The nutrient solution pH was measured at each solution exchange, and was found to average pH 5.2 for carrot, pH 5.3 for lettuce, and pH 6.0 for tomato during the study. The average pH values were used to calculate the neutral fraction and the pH-adjusted octanol-water partition coefficient for the different PPCP/EDCs, as described in Wu et al. . Only small differences in neutral fractions and log Dow values were seen between treatments for the same compound,vertical vegetable tower mostly for compounds with pKa values near the solution pH. Based on the primary ionic state in the nutrient solution, the selected PPCP/EDCs were placed in either the anionic, cationic, or neutral group .

The transpired mass for each plant was measured at every solution exchange and the data were used to calculate the cumulative transpiration . For lettuce and tomato, the different temperatures and air humidity resulted in significantly different transpired masses . The differences were smaller for carrot seedlings , likely due to the considerably smaller leaf masses of the carrot plants. The mean transpired masses in the cool-humid and warm-dry treatments during the 21 d of growth were, respectively, 65.50 ± 19.36 and 194.33 ± 30.72 g/d for lettuce, 127.04 ± 15.52 and 503.38 ± 59.76 g/d for tomato, and 16.82 ± 8.05 and 55.31 ± 26.41 g/d for carrots. For the same plant type, the warm-dry environment induced a 3-4-fold increase in plant transpiration as compared to the cool-humid environment. The dissipation of PPCP/EDCs from nutrient solution during the hydroponic growth of plants may be attributed to plant uptake and microbial degradation in the solution. The change in PPCP/EDC concentrations was measured on day 10, after 2 d incubation. In the spiked nutrient solutions without plants, most PPCP/EDCs showed limited dissipation from the solution , suggesting that these compounds were mostly stable in the nutrient solution . The only exception was atorvastatin, where 49.0% and 61.7% were not recovered for the cool-humid and warm-dry treatments, respectively . In the presence of plants, levels of PPCP/EDCs in the solution significantly decreased compared to the plant-free control. For example, after exposure to a tomato plant, about 38.8% of the initially spiked diclofenac was not recovered from the solution for the cool humid treatment and about 75.6% for the warm-dry treatment, while there was essentially no chemical loss in the plant-free container . When all compounds were pooled, removal from the solution was found to be consistently greater in the warm-dry treatment than in the cool-humid treatment. This difference was statistically significant for lettuce and tomato , but not for carrot , likely due to its very small biomass. For example, in the cool-humid and warm-dry treatments, the respective losses of gemfibrozil were 18.2% and 28.6% for carrot, 64.5% and 89.2% for lettuce, and 55.6% and 91.8% for tomato .

These trends clearly suggested that the warm-dry environment and the corresponding larger plant biomass in the warm-dry treatments, contributed to enhanced PPCP/EDC dissipation in the nutrient solution . The transpired mass over the 2 d period was compared to the measured removal of the anionic, cationic, or neutral PPCP/EDCs over the same period to assess the effect of plant transpiration on the removal of PPCP/EDCs from the nutrient solution. A significant positive relationship was found for each group of compounds , suggesting that the removal of PPCP/EDCs in the nutrient solution increased with transpiration for both ionic and neutral compounds, and across different plant species. The separation of PPCP/EDCs by ionic state in the regression analysis decreased the model residuals for both the cationic and neutral groups, as compared to a linear regression with all compounds grouped together , showing that consideration of ionic states better describes the interaction of PPCP/EDC and transpiration. Transpiration had the greatest impact on removal of neutral compounds, as shown by a slope of 0.048 for the linear regression , followed by anionic compounds , while removal of cationic compounds was least affected by transpiration . Since neutral compounds are expected to move through root membranes according to diffusion, and ionic compounds are subject to electrical effects, it is reasonable to expect that transpiration exerts the most effect on neutral compounds. Other compound characteristics besides ionic state, such as hydrophobicity and stability, may also influence PPCP/EDC dissipation in the nutrient solution and may help explain the remaining regression residuals. To evaluate the contribution of adsorption to root structures, log Dow values for each group of compounds were compared to their removals in the nutrient solution. However, no significant relationship was found for any of the treatments , suggesting that log Dow alone was not a good predictor for PPCP/EDC removal from the nutrient solution. It must also be noted that due to the small number of compounds in the cationic group, the analysis may not be sufficiently strong to be generalized for other cationic PPCP/EDCs.

To facilitate comparisons of PPCP/EDC accumulation among different compounds and between different treatments, a bio-concentration factor was calculated by dividing the concentration of a compound in a plant tissue after the 21 d cultivation to the concentration in fresh solution . In this study, atorvastatin, diclofenac, and clofibric acid were the least accumulated , while perfluorooctanoic acid, diazepam, and diuron were the most accumulated compounds . After averaging across all compounds and plant types, BCF values for root tissues were found to be significantly higher than those for leaves , with the respective mean BCF values of 51.3 and 21.0. These BCF values suggest that many PPCP/EDCs have the ability to bio-accumulate in plant tissues, and the overall accumulation into roots likely exceeds that into leaves. In addition, some PPCP/EDCs may be accumulated to relatively high levels. In general, BCFleaf values followed the order cationic ≥ neutral > anionic and BCFroot values were in the order anionic > neutral ≥ cationic,vertical farming equipments suggesting that accumulation of cationic and neutral compounds was somewhat similar. However, anionic compounds were accumulated significantly less than cationic or neutral compounds in leaves, but significantly more in the roots. The reversed trends of accumulation between leaf and root tissues were mainly caused by the behavior of anionic compounds. For anionic PPCP/EDCs, accumulation in root was significantly more than in leaf , with the mean BCF root at 72.8 while the mean BCFleaf at 3.3. In comparison, accumulation into leaf and root tissues was similar for cationic or neutral compounds . Overall, these results suggest that root tissues may accumulate high levels of anionic compounds, while in leaf tissues, cationic and neutral compounds may be more prevalent. A few other studies have considered some of these same PPCP/EDCs under hydroponic conditions, but often used higher spiking concentrations. Herkltoz et al. investigated the growth of cabbage in solution spiked with carbamazepine, sulfamethoxazole, and trimethoprim at 232.5 µg/L and found BCF values of 0.045 – 0.081 in leaf tissues and 7.04 – 10.92 in root tissues, values similar to this study for sulfamethoxazole and carbamazepine in root , but lower than carbamazepine accumulation in leaves or trimethoprim accumulation . In another study, Zhang et al. measured the uptake of clofibric acid by Scirpus validus from a culture spiked at 0.5 – 2 mg/L, and observed wetweight BCFs of 9.5 – 32.1 in leaf tissues and 6.6 – 23.2 in root tissues. These values were similar to the uptake of clofibric acid in this study . Wu et al. examined many of the same compounds at similar concentrations in nutrient solution growing cucumber, lettuce, pepper, or spinach under greenhouse conditions and observed similar BCF values in leaf and root tissues. The different environment conditions influenced bio-concentration of the PPCP/EDCs in the test plants. The mean overall BCF in the warm-dry treatment was 33.7, which was greater than that in the cool-humid treatment , although the difference was not statistically significant , likely due to the large differences in plant biomass and the wide range of chemicals used in this study. However, when BCFleaf was correlated to the transpired mass during the 21 d of plant growth, a positive correlation was observed for anionic, cationic, and neutral compounds . This result suggests that the mass flow of water caused by plant transpiration influenced the accumulation of PPCP/EDCs in leaves. Transpiration had the greatest impact on the leaf bio-concentration of cationic PPCP/EDCs, as shown by a model slope of 0.0067, while the effect was less for neutral PPCP/EDCs and much less for anionic PPCP/EDCs, suggesting that increased transpiration will have the greatest effect on leaf uptake of cationic compounds and little effect on leaf uptake of anionic compounds. This result is somewhat different than that seen for the removal of PPCP/EDCs from the nutrient solution. The difference may be attributed to other factors in addition to plant uptake, including microbial degradation in the nutrient solution.

In contrast, a relationship between BCFroot and transpired mass was only observed for the neutral group . High residuals in the linear model analysis further suggested that other factors, such as plant species, metabolism after uptake, and likely other compound properties, may also be important in describing PPCP/EDC accumulation into plant tissues. For anionic compounds, it is known that the negative charged molecules may experience repulsion from negatively charged root cell membranes, and that plant accumulation of anions may be mainly due to diffusion of the neutral fraction through the membrane and ion trap effects . A comparison of BCF values of anionic compounds in all plants with their respective log Dow showed a negative correlation for BCF leaf or BCF root , suggesting that anionic compounds with lower effective hydrophobicity had higher accumulation in the leaf or root tissues . This effect was greatest for root tissues, and the slope of the linearized regression was -54, while for leaf tissues the slope was only -0.63, suggesting other factors besides hydrophobicity may have a larger impact on the aerial uptake of anionic compounds. The cationic fraction of a compound may slowly diffuse through plant membranes due to electrical attraction between the positively charged molecules and the negatively charged cell membrane, while the neutral fraction may diffuse with preference to compounds of moderate hydrophobicity . In this study, a positive correlation was observed between BCF leaf and log Dow for cationic PPCP/EDCs in all plants , suggesting that more hydrophobic cationic PPCP/EDCs have a higher accumulation potential in leaf tissues. Further, this effect was relatively strong, with a slope of 10 for the linear regression, as compared to a slope of 6.6 for neutral compounds or -0.63 for anionic compounds. It has been shown that the accumulation of cationic organic compounds in aerial tissues was the greatest for compounds with log Kow between 2.5 –5.5 . In this study, for example, uptake of dilantin into the leaves was greater than that of trimethoprim . In comparison, no significant correlation was observed between BCFroot and log Dow for cationic compounds , suggesting that other factors also contributed to the accumulation of cationic compounds in roots. However, it must be stated again that the limited pool of cationic compounds in this study hampered a more conclusive examination of cationic PPCP/EDCs and that the assumption merits further validation.

Posted on

The effect of this cumulative dose of multiple PPCP/EDCs is unknown

For instance, the half-lives of triclosan and estrone increased from 5.9 d to 8.9 d and from 0.6 d to 1.1 d, respectively, in soils previously exposed to WWTP effluent as compared to unexposed soils . Extensive microbial transformation results in the mineralization of PPCP/EDCs in soil to CO2 and hence complete decontamination. Mineralization is exclusively mediated by microbial transformations . For example, in 3 soils, 14C-estrone showed 15 – 85% mineralization after 100 d of incubation . About 15% of 14C-bisphenol A was mineralized after aerobic incubation in 4 soils for 120 d , while only 0.49 – 0.58%of sarafloxacin was mineralized after 80 d of aerobic incubation in 3 soils . After 27 d, 50% of 14C-naproxen was mineralized . This variability shows that mineralization is compound and soil specific, similar to other microbial transformation processes. However, at present there is a general scarcity of information, making it difficult to predict the relative impact of mineralization in the overall fate and risk of PPCP/EDCs in the soil-plant-human continuum. Microbial transformations may produce many intermediate products before the compound is fully mineralized or bound in soil. The formation of transformation intermediates in soil poses unknown risks as the new products may have biological activity . Due to analytical challenges in identifying unknown products in environmental matrices, very little information on transformation intermediates is available for PPCP/EDCs . A study showed that diclofenac was transformed to 5-hydroxydiclofenac and its p-benzoquinone imine in a bioreactor with river sediment, though the levels were not quantified . While the p-benzoquinone imine was formed transiently and in small quantities, it is the known to have high hepatoxic potential . In a separate study using an activated sludge bioreactor, 7 transformation products of diclofenac were found but none were identified . Ibuprofen formed hydroxyibuprofen in a pilot sewage plant and carboxyibuprofen in an oxic biofilm reactor . Overall, knowledge of PPCP/EDC transformation intermediates in the soil is extremely limited and warrants further investigation. The application of treated wastewater, bio-solids, or manure to land creates a potential for plants to take up PPCP/EDCs ,vertical hydroponics which may be beneficial in areas of phytoremediation, but in agricultural areas may contaminate food crops and create a possible route of human exposure through ingestion .

The few studies that have examined PPCP/EDC uptake by plants have reported accumulation by a variety of edible and non-edible plants, with accumulation varying among compounds, plant species, plant tissues, exposure concentrations, and exposure durations . While potential for plant uptake has been shown in laboratory settings, many of these experiments used artificially high concentrations that are not representative of environmental levels of PPCP/EDCs. The extent of plant accumulation in the environment has been scarcely studied. Calderón-Preciado et al. analyzed alfalfa and apple trees irrigated with water impacted by WWTP effluentand identified PPCP/EDCs in plant tissues at ng/kg – µg/kg levels, verifying that PPCP/EDCs are susceptible to plant accumulation under realistic agronomic conditions. Due to the extensive suite of PPCP/EDCs, it is not feasible to empirically measure plant uptake of each compound. Therefore, it is crucial to develop a mechanistic understanding of their accumulation to inform risk assessment. Many factors affect plant uptake of organic compounds, including compound hydrophobicity, ionization behavior, soil pH, soil organic matter, and plant transpiration . Uptake is generally a passive process, occurring by diffusion that is driven by water potential gradients . Due to transpiration driving the translocation of water through the plant, compounds which are neutral, polar, persistent, and non-volatile have the potential to concentrate in plants up to 100 times the concentration in soil . Most PPCP/EDCs are non-volatile , making this accumulation pathway relevant for some PPCP/EDCs. Ionic compounds, like phenoxy acid herbicides, have the possibility to be taken up by active transport, perhaps through processes designed for uptake of essential nutrients , and may reach higher concentrations than would be expected through passive diffusion . Since some PPCP/EDCs exist primarily in an ionic state , these compounds may potentially accumulate to high levels in plant tissues. The pH of the soil-water or hydroponic solution affects the fraction of ionizable compounds that is in the ionic form. For compounds that are partly ionized at environmental pH levels, basic compounds have increased uptake and acidic compounds have reduced uptake as pH increases , due to changes in the prevalence of the neutral fraction and ion-trapping effects as discussed below.

Accumulation in plant tissues is also related to the tissue composition. Hydrophobic compounds may partition to lipids, where they have the potential to accumulate. Therefore, plants with higher lipid contents may accumulate a compound to a greater degree . The partitioning of a compound to plant lipids is related to its Kow, as discussed below. In comparison, polar compounds are expected to reach equilibrium with the water present in plants and with relatively polar carbohydrates and proteins, which suggests accumulation of these compounds will likely be less extensive . No single model is currently available that accurately accounts for all of these factors , and very little validation of plant uptake models has been done for PPCP/EDCs.Compounds may be taken up by plants when plant roots reach contaminated areas and by mass flow or diffusion of dissolved compounds to roots . Entry is typically by diffusion of neutral compounds across the root membrane, and for ionizable compounds by a combination of diffusion of the neutral fraction and electrostatic interactions by the ionic fraction . A positive relationship has been shown between hydrophobicity and root uptake of neutral pesticides and other neutral compounds . The partitioning of neutral compounds to plant lipids is very similar to the partitioning to octanol, and thus uptake models use log Kow values with adjustments for other factors, including the amount of lipids in the tissue . Based on the partitioning behaviors of neutral compounds and that 1% of barley roots were lipids, Chiou et al. predicted that accumulation into root lipids compared to the rest of the root tissue accounted for 15% of uptake for compounds with log Kow ≤ 1, but ~100% of compounds with log Kow of > 3,hydroponic vertical farming systems showing that while lipids make up a very small part of plant tissue, they greatly affect accumulation behavior and may explain some uptake differences among plant species . For neutral compounds, root uptake is expected to be the greatest for compounds with high hydrophobicity and for plants with high lipid content . Models developed for neutral compounds may be inappropriate to describe the behavior of ionizable compounds, which includes many PPCP/EDCs. The accumulation of compounds in aerial tissue can occur via deposition from volatilized compounds, direct contact with irrigation or amendment materials, and translocation from root tissues . Since most PPCP/EDCs are polar and nonvolatile, volatilization and deposition is expected to be a very minor input for aerial tissue uptake . The extent of organic compound uptake by direct contact is not very well characterized and warrants further investigation. In general, it is expected to proceed by diffusion similar to root uptake. Most studies have focused on the translocation of PPCP/EDCs from roots, which is likely to become more important than direct contact with increased use of drip and other water-conserving irrigation methods that reduce the likelihood of direct contact between plant leaves and irrigation water. Aerial accumulation of neutral organic contaminants from root tissue involves movement of compounds into xylem and then translocation to aerial parts.

Concentrations in xylem are lower than root concentrations due to hydrophobic partitioning to root tissues, suggesting that hydrophobic compounds will be predominantly retained by roots while a greater portion of hydrophilic compounds will move to xylem and be translocated to aerial tissues . Accumulation in aerial tissue competes with compound return to roots tissues via phloem, and occurs by hydrophobic partitioning of compounds to lignin, which usually has much greater affinity for organic chemicals than carbohydrates or cellulose do . Overall, studies suggest that the maximum leaf uptake of neutral compounds may occur at log Kow values in the range of 1.8 – 3.08 . However, many of these studies utilized hydroponic systems, and it has been suggested that in a soil-plant system where uptake is in competition with soil sorption, that the optimal log Kow value would be closer to 0.75 for soil with 6% organic matter,1.25 for 1.25%, and 2 for 0.25% . Similar to root uptake, aerial uptake of ionizable PPCP/EDCs is a combination of neutral fraction uptake, which can be described with log Dow values, and ionic fraction uptake, which is controlled by electrical interactions. Anions are repulsed from all cell membranes except the tonoplast of vacuoles in root cells, so uptake of anionic PPCP/EDCs by xylem and aerial tissue is predicted to be small, except in cases of ion trapping . Cations are electrically attracted to most cell membranes, enhancing diffusion to many plant parts and resulting in generally moderate uptake ability, which may be further enhanced in alkaline soils by ion trap effect . After PPCP/EDCs have been taken up into plant tissues, a number of biological processes may occur that will reduce the bio-available fraction of the parent PPCP/EDC. Xenobiotics in general are quickly modified in a plant cell by enzymes, such as hydrolases or cytochrome p450, to enable conjugation with glutathione or glucose . The conjugated compounds may then be catabolized, creating a variety of transformation products, which are eventually mineralized or incorporated into the plant tissue . The pathways andrates of these metabolic processes are likely specific to each compound and plant species . As organic contaminants, PPCP/EDCs may be metabolized in plants to form transformation products and non-extractable residue, but this area needs further research. In one of the few studies available, Bokern and Harms used cell suspension cultures to identify toxicity and metabolism of 14C-nonylphenol. Plant species which were resistant to toxicity were most efficient at incorporating the compound into cell walls, primarily associated with lignin but also with pectin and hemicellulose. Extractable polar metabolites were also detected, showing that plant cells metabolized the nonylphenol into transformation products and non-extractable residue. In another study, Macherius et al. incubated carrot cell cultures and whole carrots with triclosan, methyl triclosan, and triclocarban. Triclosan was taken up and converted to 8 different conjugated compounds in cells due to bonding at its phenol moiety, but triclocarban and methyl triclosan were found to be taken up and not metabolized. These results suggest that metabolism of PPCP/EDCs in plant may vary widely with the compound, and some compounds may exist principally in their original form in plant tissue. This area needs more research due to its human health implications. Due to the scarcity of information about PPCP/EDC accumulation in edible plants, especially for real environmental situations, the potential of PPCP/EDC residue to have a biological effect in humans is unknown. Matamoros et al. predicted that human consumption of vegetable crops irrigated with water containing PPCP/EDCs would cause an exposure of 500 ng/d of each compound, a level well below the therapeutic dose for individual pharmaceuticals but in an active range for EDCs. Based on the accumulation in radish and ryegrass grown in soil with 0.4 – 19 µg/kg of carbamazepine, diclofenac, fluoxetine, propranolol, and triclosan, Carter et al. calculated that humans might consume 0.01 – 0.21% of an acceptable daily intake for each compound in root vegetables and 0.09 – 3.81% for leaf vegetables. The major exception in the study was the high accumulation of triclosan, which was predicted to reach 83.8% of ADI in leaf tissues, nearing the acceptable limit. These studies focused on the extractable parent compound measured in laboratory uptake studies. As discussed above, it is likely that a large portion of the accumulated PPCP/EDC may be in the form of transformation products, conjugated compounds, and non-extractable residue. While non-extractable residues of xenobiotics have significantly reduced biological activity in plants and appear to be primarily not bio-available to animal metabolism, conjugated compounds may be cleaved during animal metabolism andpotentially exert toxic effects . The presence of conjugated and transformed PPCP/EDCs in plant tissue is poorly understood and the health risks from them are far from clear. Pharmaceuticals and other anthropogenic chemicals are increasingly used around the world .

Posted on

The rate of methylation or demethylation appeared to be molecule -specific

Biologically mediated transformations such as methylation and demethylation may also occur in organisms such as D. magna after their uptake of CECs, which may further influence their toxicity. Methylation and demethylation in D. magna were investigated after exposing D. magna to the individual compounds. Methylation of the selected demethylated CECs was negligible, as no methylated product was detected in D. magna after its exposure to the corresponding demethylated counterpart. However, demethylation of diazepam, methylparaben and naproxen in D. magna was evident , while acetaminophen was not detected in D. magna exposed to Macetaminophen. The demethylation of methylparaben was limited, with a peak concentration of DM-methylparaben at 0.5 ± 0.0 nmol g -1 in D. magna after 12 h of exposure to 1 mg L-1 methylparaben. This represented only about 2.0% of the molar equivalent of methylparaben in D. magna. The demethylation of diazepam was found at similar levels, with DM-diazepam at 4.4% molar equivalent of diazepam. Interestingly, the molar equivalents of the demethylated derivatives increased over time during the depuration phase, even though the overall concentrations generally decreased over time. For example, the molar equivalents of DM-diazepam and DM-methylparaben reached 33.5% and 54.8% at the end of depuration, respectively. This may be attributed to the fact that demethylation continued during the depuration phase, which may have influenced the apparent depuration of these compounds .The demethylation of naproxen in D. magna was the most pronounced among the four methylated compounds,vertical garden growing with DM-naproxen generally detected at levels higher than naproxen itself during both the uptake and depuration phases . DM-naproxen was formed quickly in D. magna after exposure to naproxen, with 21.5 ± 2.7 nmol g-1 after 12 h into the uptake phase, which was significantly higher than that of the parent naproxen .

Similar to DM-diazepam and DMmethylparaben, the molar equivalent of DM-naproxen also continued to increase during the depuration phase. At the end of depuration, DM-naproxen accounted for approximately 88.9% of the total naproxen and DM-naproxen residues in D. magna. The high proportion of DM-naproxen in D. magna also suggested that demethylation was the primary metabolism pathway of naproxen in D. magna. To better understand the demethylation of CECs in D. magna, the formation rates of DM-diazepam, DM-methylparaben and DM-naproxen were estimated by simulating their formation over the initial 12-h period, during which good linear relationships between their formation and time were present . Formation rates showed no significant differences between DM-diazepam and DM-methylparaben. However, the formation rate of DM-naproxen was significantly greater than DM-diazepam or DM-methylparaben. Based on their respective chemical structure , the demethylation of diazepam and naproxen appears to differ slightly from that of methylparaben. While the demethylation of methylparaben involves the removal of a methyl group from a carboxyl group, which may be catalyzed bycarboxylesterases,CYP450s,or through non-enzymatic hydrolysis,the demethylation of M-acetaminophen, diazepam and naproxen reflects the removal of a methyl group from an amide or hydroxyl group, which likely is catalyzed mainly by CYP450s.Previous studies showed that carboxylesterases play a more important role in drug metabolism in invertebrates due to the lower activity of CYP450s.The more significant demethylation observed for naproxen in comparison to methylparaben suggests that CYP450s may also play an important role in the metabolism of such substrates in aquatic invertebrates. The observed significant differences in the demethylation rates of diazepam and naproxen imply that CYP450s in aquatic invertebrates like D. magna may exhibit different levels of activity towards different CECs.In vivo half-lives of the test compounds were derived from the depuration rate during the 24-h depuration phase in D. magna. The in silico half-life was estimated from the primary bio-transformation rate in fish and normalized to a 10 g fish at 15 °C based on the inherent characteristics of the QSAR model.

Similar to BCF values, in vivo and in silico half-lives could not be compared directly between the different organisms. Hence, the relative persistence of test compounds was calculated for evaluation. As shown in Table 2, in silico predictions suggest that methylation may prolong the persistence of CECs in fish. This was in contrast to the in vivo results in D. magna, which showed that methylation generally shortened the persistence of CECs. As mentioned above, methylated CECs generally accumulated faster with a larger ku value during the uptake phase, but dissipated rapidly during the depuration process. Considering that biota residing in wastewater effluent-dominated streams often experience pseudo-persistent exposure to CECs due to the constant discharge of effluents from WWTPs, uptake rates may be more important in regulating the accumulation of CECs in aquatic organisms dwelling in the impacted system. The prolonged bio-transformation half-lives of methylated CECs should be validated under field conditions. Overall, in silico predictions and experimental measurements were in agreement for the influences introduced by methylation or demethylation. This highlights the feasibility of incorporating QSAR models to evaluate the potential influence of common transformations such as methylation and demethylation on the environmental risks of CECs to non-target organisms in impacted ecosystems. Simple transformations such as methylation and demethylation contribute to the proliferation of the numbers of CECs and diverse structures in environmental compartments impacted by e.g., wastewater effluent.This study showed that these transformations can alter the physicochemical properties of CECs, resulting in changes in their environmental processes such as bio-accumulation and acute toxicity in aquatic organisms. These transformations of man-made chemicals may also take place within a non-target organism after their accumulation from the ambient environment.

Certain transformations, like methylation, likely result in enhanced bio-accumulation and increased toxicity in non-target organisms. Although not considered in this study, halogenation of man-made chemicals, such as gemfibrozil, 4-nonylphenol and naproxen, during the disinfection process in WWTPs, has also been reported, and the halogenated products generally exhibited increased bio-accumulation and toxicity to aquatic invertebrates.Due to the presence of numerous CECs in sources such as wastewater effluents and sediments, the co-existence of various TPs presents an additional challenge in addressing the overall environmental risks of man-made chemicals. It is important to note that high concentrations of test CECs and their corresponding methylated or demethylated TPs were used in this study in order to derive the LC50values and examine conversions in D. magna; these concentrations were above environmentally relevant levels. However, previous studies suggested that BCFs may be greater at lower exposure concentrations.Therefore, the effect of methylation or demethylation on bio-accumulation of CECs may be more pronounced than what was observed in this study. The environmental occurrence and concentrations of methylated or demethylated TPs are largely unknown for most CECs. Further research into the occurrence of TPs in different environmental compartments is needed to gain knowledge about the realistic exposure levels and to refine risk assessment. A major challenge in comprehensively assessing environmental risks is the sheer number of CECs and their TPs. It is unrealistic to experimentally evaluate transformation-induced changes in their environmental behaviors and toxicological profiles for all CECs.The incorporation of well-established QSAR models to predict essential chemical properties and environmental risk markers, such as hydrophobicity and lipophilicity, bio-accumulation potential, and acute toxicity, may help prioritize TPs with enhanced biological activities.This approach can be used to more effectively direct future research efforts to better understand the environmental significance of common transformation reactions for CECs. Four CECs and their methylated or demethylated TPs were comparatively evaluated for their uptake into A. thaliana cells or by wheat seedlings. The methylated compounds, generally more hydrophobic with a greater log Kow and log Dow,equipment for vertical farming often displayed a greater accumulation potential in both plant models as compared to their demethylated counterparts, with the exception of acetaminophen/M-acetaminophen in A. thaliana cells. The influence of methylation and demethylation on the translocation of CECs in wheat plants was molecular-specific. Methylation caused a significant increase in the translocation of acetaminophen, but a significant decrease for DM-diazepam. Methylation also generally prolonged the persistence of CECs in both A. thaliana cell culture media and wheat seedling hydroponic solution. A significant linear relationship was observed between log Dow and log BCF, indicating that the generally increased accumulation of methylated compounds may be attributed to their higher hydrophobicity. Results from this study suggested that common transformations such as methylation and demethylation may affect the persistence and accumulation of CECs in plants, and their role should be considered to obtain a more comprehensive understanding of the risks of CECs in the terrestrial environment including agro-food systems.

The interconversions between CECs and their methylated or demethylated TPs were evaluated in A. thaliana cells and wheat seedlings after their uptake. The methylation demethylation cycle was observed in both plant models, with demethylation generally taking place at a greater degree than methylation. Computation results showed that the chemical bond strength between the methyl group and the major molecular fragment in the methylated CECs followed a general order of methylparaben < diazepam < naproxen < M-acetaminophen, a pattern reflective of experimental observations for demethylation in A. thaliana cells. Future studies considering more chemical structures would help strengthen such QSAR models so that the potential for simple transformations such as methylation and demethylation may be predicted in the absence of experimental data. The acute toxicity of selected CECs and their methylated or demethylated TPs was further assessed by exposing D. magna to individually compounds. Methylation or demethylation resulted in changes in the acute toxicity for most CECs, and the influence was compound-specific. Methylation led to a significant increase in the acute toxicity of DM-methylparaben and DM-naproxen, but a decrease for acetaminophen. A significant negative linear relationship was observed between log LC50 values and log Dlipw values, indicating that as log Dlipw increased, the acute toxicity generally increased. Methylation increased the bio-accumulation in D. magna for acetaminophen, DM-methylparaben and DM-naproxen, and the increased bio-accumulation likely underlined the increases in acute toxicity for methylated compounds. In D. magna, active demethylation of diazepam, methylparaben and naproxen was observed, with the demethylation of naproxen especially pronounced, suggesting that enzymes in D. magna exhibited different levels of activity towards different substrates. QSAR models were used to predict changes in acute toxicity and bio-accumulation as a result of methylation, and the predicted values were in good agreement with experimental observations. The exploratory research presented in this dissertation clearly showed that simple transformations such as methylation and demethylation can significantly change the physico chemical properties of CECs and subsequently cause changes in their environmental behaviors such as accumulation by plants and aquatic organisms, toxicity and persistence. Methylation generally leads to increased hydrophobicity and further greater bio-accumulation and acute toxicity. However, exceptions were also observed in this study, suggesting that specific molecular structures may respond differently to the impact of simple transformations. QSAR models using molecular descriptors have the capability to predict the easiness of transformation reactions such as methylation and demethylation, the subsequent changes in physicochemical properties from such transformations, and further, the ensuing changes in bio-accumulation, translocation, and toxicity. Such models should be calibrated with more experimental observations and by the inclusion of more diverse structures. Such predictive tools are extremely valuable, given the enormous number of CECs and their transformation products, which renders experimentation-based approaches largely infeasible. This dissertation research highlights the prevalence of simple transformations such as methylation and demethylation in the environment, and the need to consider such transformations in achieving a more comprehensive understanding of the environmental fate and risks of CECs.Results from this dissertation research and a few other studies showed that simple transformations can effectively influence the environmental behaviors of CECs, and the effect is specific to molecular structures. Changes in bio-accumulation and toxicity due to transformations should be further evaluated under environmentally relevant conditions. The greatest challenge to understanding the environmental risks of CECs is the sheer number of CECs and their metabolites. In the absence of experimental data, predictive tools such as QSAR models and computational chemistry should be used to predict the possibility for the occurrence of transformations as well as the changes in physicochemical properties accompanying these transformations. Likewise, modeling may be also used to estimate changes in environmental behaviors and risks for CECs that are susceptible to transformations. It must be noted that only methylation and demethylation were considered in this research.