Adjusted associations between a 10-fold increase in the amount of fumigants applied within 8 km of the home and the highest lung function measurements are presented in Table 4. We did not observe any significant adverse relationships between prenatal or postnatal fumigant use within 8 km and lung function. A 10-fold increase in wind-adjusted prenatal methyl bromide use within 8 km was associated with higher FEV1 and FEF25–75 . Additionally, a 10-fold increase in wind-adjusted prenatal chloropicrin use within 8 km was positively associated with FEF25–75 . Associations between methyl bromide and chloropicrin use and lung function observed in the prenatal exposure period were not observed in the postnatal period. Results were similar, although no longer statistically significant, for prenatal methyl bromide and chloropicrin use within 5 km of residences . There were no associations between fumigant use within 3 km of residences and lung function . We did not observe associations between postnatal fumigant use at any distance and lung function measurements or between fumigant use during the year prior to the assessment and lung function measurements .In sensitivity analyses using multi-variable models including other pesticide exposures that have been previously related to respiratory symptoms and lung function including childhood urinary DAP metabolites , proximity to agricultural sulfur use during the year prior to lung function assessment and prenatal DDT/DDE blood concentrations , the results were very similar to those presented in Tables 3 and 4. For example,blueberry plant size the relationships between prenatal methyl bromide use within 8 km were very similar for FEV1 and FEF25–75 .
Prenatal fumigant use was generally not correlated with other pesticide exposures that we found to be associated with lung function in this cohort, except for weak correlations between agricultural sulfur use within 1 km during the year prior to spirometry and prenatal use of metam sodium and 1,3 – DCP with r = 0.14 and r=0.26 respectively. The results were very similar when we only included children with two acceptable reproducible maneuvers in the analyses . The results were also similar when we excluded those currently using asthma medication, excluded the one outlier for FEV1 models or used inverse probability weighting to adjust for participation bias . Risk ratios estimated for asthma symptoms and medication using Poisson regression were nearly identical to the ORs presented in Table 3 and Supplemental Table 2. We did not observe effect modification by asthma medication use. Maternal report of child allergies modified the relationship between FEV1 and prenatal proximity to methyl bromide use and we only observed higher FEV1 among children without allergies . After adjusting for multiple comparisons, none of the associations reached significance at the critical p-value 0.002 based on the Benjamini-Hochberg false discovery rate. This is the first study to examine lung function or respiratory symptoms in relation to residential proximity to agricultural fumigant use. We found no significant evidence of reductions in lung function or increased odds of respiratory symptoms or use of asthma medication in 7-year-old children with increased use of agricultural fumigants within 3 – 8 km of their prenatal or postnatal residences. We unexpectedly observed a slight improvement in lung function at 7 years of age with residential proximity to higher methyl bromide and chloropicrin use during the prenatal period and this improvement was limited to children without allergies.
Although these results remained after adjustment for other pesticide exposure measures previously related to respiratory symptoms and lung function in our cohort, they do not remain significant after adjustment for multiple comparisons. There is a strong spatial pattern of methyl bromide and chloropicrin use during the pregnancy period for our study because of heavy use on strawberry fields near the coast at the northern portion of the Salinas Valley . There could be other unmeasured environmental or other factors that are confounding the relationship we observed between higher prenatal fumigant use and improved lung function. Previously published studies of prenatal exposure to air pollutants and lung function have generally observed links to alterations in lung development and function and to other negative respiratory conditions in childhood, and plausible mechanisms include changes in maternal physiology and DNA alterations in the fetus . Improved lung function was associated with higher estimates of recent ambient exposure to hydrogen sulfide in a study of adults living in a geothermal area of New Zealand . However, hydrogen sulfide has been shown to be an endogenously produced “gasotransmitter”, with anti-inflammatory and cytoprotective functions , and is being explored for its use for protection against ventilator-induced lung injury . In previous studies of this cohort, we found increased odds of respiratory symptoms and lower FEV1, and FVC per 10-fold increase of childhood average urinary concentrations of metabolites of organophosphate pesticides . Other studies of prenatal pesticide exposure and respiratory health in children have mostly evaluated exposure using cord blood concentrations of DDE, a breakdown product of DDT, and have observed an increased risk of respiratory symptoms and asthma with higher levels of DDE . Most studies of postnatal pesticide exposure and respiratory health in children have utilized self-reported information from mothers to assess pesticide exposure and have observed higher odds of respiratory disease and asthma with reported pesticide exposure . None of the previous studies of pesticide exposure and respiratory health have specifically evaluated fumigants.
Another strength of the study is that CHAMACOS is a prospective cohort followed since pregnancy with extensive data on potential confounders of respiratory health and other measures of pesticide exposure. Our study also had some limitations. We did not have information on maternal occupational exposure to fumigants or the geographic location of maternal workplaces during pregnancy, and we did not have the location of schools during childhood. These limitations likely resulted in some exposure misclassification during both the prenatal and postnatal periods. An important consideration in this study is that we estimated fumigant exposure using proximity to agricultural fumigant applications reported in the PUR data, which is not a direct measure of exposure. However, the PUR data explains a large amount of the variability of measured fumigant concentrations in outdoor air . In conclusion, we did not observe adverse associations between residential proximity to agricultural fumigant use during pregnancy or childhood and respiratory health in the children through 7 years of age. Although we did not observe adverse effects of fumigants on lung function or respiratory symptoms in this analysis,plant raspberry in container we have seen adverse associations in previous analyses of the CHAMACOS cohort between residential proximity to higher fumigant use and child development. We observed an association between higher methyl bromide use during the second trimester of pregnancy and lower birthweight and restricted fetal growth . We also observed decreases of ~2.5 points in Full-Scale intelligence quotient at 7 years of age for each 10-fold increase in methyl bromide or chloropicrin use within 8 km of the child’s residences from birth to 7 years of age . Future studies are needed in larger and more diverse populations with a greater range of agricultural fumigant use to further explore the relationship with respiratory function and health. It is typically assumed that output levels and prices in the U.S. food processing sector are directly linked to the availability and prices of the agricultural products or materials used for production. However, the traditional link between farm and food prices and production may be weakening. Adaptations in input costs and food consumption patterns are leading to changes in the production structure and technology of the food processing industries, that in turn affect demand patterns for primary agricultural materials. Such structural changes have been documented not only by anecdotal evidence, but in studies such as Goodwin and Brester, and Morrison and Siegel. In particular, Goodwin and Brester find that value-added by manufacture, both per worker hour and as a percentage of sales, increased in the 1980s in the U.S. food and kindred products industry overall, possibly implying an undermining of MA demand. Various economic and behavioral factors underlie these trends. As noted by Goodwin and Brester, relative prices of inputs important to food manufacturing, such as energy and labor prices relative to those for raw materials, shifted significantly in the past couple of decades.
The business environment also has experienced quite a transformation, including market structure and regulatory changes in the early 1980s. Tax changes have, for example, had a direct impact on relative input prices, by affecting the prices of capital inputs. Perhaps even more important than these alterations in the economic climate facing food processors are adaptations in food demand patterns. The fact that a greater proportion of adults are in the labor force today causes a higher demand for food products that require little home preparation time; they are at least in part prepared at the processing plant. These modifications in dietary preferences, combined with changes in food technology that allow processors to adapt foods to meet those preferences, could lead to more in plant processing of agricultural commodities. Other technical changes associated with capital equipment and the quality of agricultural materials, could also have an impact on the relative demand for agricultural products. These adaptations in food product costs, demand, and characteristics may mean that food processors are responding by altering their input composition. If they are using more capital, skilled labor, and non-agricultural materials to produce food products than in the past, these factors could become increasingly important elements in processors’ costs relative to agricultural commodities. The corresponding decline in agricultural materials input intensity is likely to result in weaker effects of changes in agricultural commodity prices on food prices, which has important impacts on both consumers of the final product and producers of the raw agricultural materials. To address these issues, this study assesses the role of changes in food product demand, input prices, and food processing technology on food processors’ costs and output prices, with a particular focus on the use of agricultural commodities as compared to other factor inputs. Our analysis of cost structure and input composition changes in the U.S. food processing industries is based on a cost-function representation of production processes in these industries. In our model we recognize a full range of substitution patterns among capital, labor, energy, agricultural materials, food materials and “other” materials inputs resulting from input price changes or technological factors. This allows us to explore modifications in input mix, costs and commodity prices resulting from changing agricultural commodity prices and output demand. It also facilitates consideration of technological factors affecting MA demand and production costs such as the quasi-fixed nature of capital , scale economies, technical change associated with either time trends or capital composition, and agricultural innovations or market power embodied in the MA input price. The model is estimated using data on 4-digit SIC level U.S. food processing industries, and the results summarized according to time period and 3-digit code . The base price and quantity data for output, capital, labor, and materials are from the National Bureau of Economic Research Productivity Database. The materials breakdown was drawn from data in the Census of Manufactures, which are only available at 5-year intervals – from 1972 to 1992. We therefore have a panel of data for 34 industries and 5 time periods, which are distinguished by fixed effects for estimation.Our empirical results suggest that agricultural materials demand has been affected by various technological and market characteristics of the food processing industry. Although own price effects have had the potential to limit MA demand, growth in the price of agricultural materials has fallen over time, and in the effective price has fallen even lower, so this effect was essentially erased – or even reversed direction – by the end of the 1980s. Substitution effects have also contributed to MA demand. Rising capital costs, especially in effective units, and its implied limitations on production flexibility, have particularly enhanced MA substitution. Scale effects have had a somewhat ambiguous effect, since MA use has increased slightly more proportionately than output increases in effective units, but less than the use of intermediate food products, so MA demand, especially in traditionally measured units, has weakened relative to these substitute inputs. We also, however, find a strong and increasing downward trend in MA demand over time.