There are no biomarkers available to assess human exposure to fumigants in epidemiologic studies . Residential proximity to fumigant use is currently the best method to characterize potential exposure to fumigants. California has maintained a Pesticide Use Reporting system which requires commercial growers to report all agricultural pesticide use since 1990 . A study using PUR data showed that methyl bromide use within ~8 km radius around monitoring sites explained 95% of the variance in methyl bromide air concentrations, indicating a direct relationship between nearby agricultural use and potential community exposure . In the present study, we investigate associations of residential proximity to agricultural fumigant usage during pregnancy and childhood with respiratory symptoms and pulmonary function in 7-year-old children participating in the Center for the Health Assessment of Mothers and Children of Salinas , a longitudinal birth cohort study of primarily low-income Latino farm worker families living in the agricultural community of the Salinas Valley, California. We enrolled 601 pregnant women in the CHAMACOS study between October 1999 and October 2000. Women were eligible for the study if they were ≥18 years of age, <20 weeks gestation, planning to deliver at the county hospital, English or Spanish speaking,square plant pot and eligible for low-income health insurance . We followed the women through delivery of 537 live-born children. Research protocols were approved by The University of California, Berkeley, Committee for the Protection of Human Subjects. We obtained written informed consent from the mothers and children’s oral assent at age 7. Information on respiratory symptoms and use of asthma medication was available for 347 children at age 7.

Spirometry was performed by 279 of these 7-year-olds. We excluded participants from the prenatal analyses for whom we had residential history information for less than 80% of their pregnancy. We excluded participants from the postnatal analyses for whom we had residential history information for less than 80% of the child’s lifetime from birth to the date of the 7 year assessment. Prenatal estimates of proximity to fumigant applications and relevant covariate data were available for 257 children and postnatal estimates of proximity to fumigant applications and relevant covariate data were available for 276 children for whom we obtained details of prescribed asthma medications and respiratory symptoms. Prenatal estimates of proximity to fumigant applications and relevant covariate data were available for 229, 208, and 208 children for whom we had FEV1, FVC and FEF25–75 measurements, respectively. Postnatal estimates of proximity to fumigant applications and relevant covariate data were available for 212, 193, and 193 children with FEV1, FVC and FEF25–75 measurements, respectively. A total of 294 participants were included in either the prenatal or postnatal analyses. Participants included in this analysis did not differ significantly from the original full cohort on most attributes, including maternal asthma, maternal education, marital status, poverty category, and child’s birth weight. However, mothers of children included in the present study were slightly older and more likely to be Latino than those from the initial cohort. Women were interviewed twice during pregnancy , following delivery, and when their children were 0.5, 1, 2, 3.5, 5, and 7 years old. Information from prenatal and delivery medical records was abstracted by a registered nurse. Home visits were conducted by trained personnel during pregnancy and when the children were 0.5, 1, 2, 3.5 and 5-years old. At the 7-year-old visit, mothers were interviewed about their children’s respiratory symptoms, using questions adapted from the International Study of Asthma and Allergies in Childhood questionnaire . Additionally, mothers were asked whether the child had been prescribed any medication for asthma or wheezing/whistling, or tightness in the chest. We defined respiratory symptoms as a binary outcome based on a positive response at the 7- year-old visit to any of the following during the previous 12 months: wheezing or whistling in the chest; wheezing, whistling, or shortness of breath so severe that the child could not finish saying a sentence; trouble going to sleep or being awakened from sleep because of wheezing, whistling, shortness of breath, or coughing when the child did not have a cold; or having to stop running or playing active games because of wheezing, whistling, shortness of breath, or coughing when the child did not have a cold. In addition, a child was included as having respiratory symptoms if the mother reported use of asthma medications, even in the absence of the above symptoms.

Latitude and longitude coordinates of participants’ homes were collected during home visits during pregnancy and when the children were 0.5, 1, 2, 3.5 and 5 years old using a handheld Global Positioning System unit . At the 7-year visit, mothers were asked if the family had moved since the 5-year visit, and if so, the new address was recorded. Residential mobility was common in the study population. We estimated the use of agricultural fumigants near each child’s residence using a GIS based on the location of each child’s residence and the Pesticide Use Report data . Mandatory reporting of all agricultural pesticide applications is required in California, including the active ingredient, quantity applied, acres treated, crop treated, and date and location within 1-square-mile sections defined by the Public Land Survey System . Before analysis, the PUR data were edited to correct for likely outliers with unusually high application rates using previously described methods . We computed nearby fumigant use applied within each buffer distance) for combinations of distance from the residence and time periods . The range of distances best captured the spatial scale that most strongly correlated with concentrations of methyl bromide and 1,3-DCP in air . We weighted fumigant use near homes based on the proportion of each square-mile PLSS that was within each buffer surrounding a residence. To account for the potential downwind transport of fumigants from the application site, we obtained data on wind direction from the closest meteorological station . We calculated wind frequency using the proportion of time that the wind blew from each of eight directions during the week after the fumigant application to capture the peak time of fumigant emissions from treated fields . We determined the direction of each PLSS section centroid relative to residences and weighted fumigant use in a section according to the percentage of time that the wind blew from that direction for the week after application.

We summed fumigant use over pregnancy , from birth to the 7-year visit and for the year prior to the 7-year visit yielding estimates of the wind-weighted amount of each fumigant applied within each buffer distance and time period around the corresponding residences for each child. We log10 transformed continuous fumigant use variables to reduce heteroscedasticity and the influence of outliers, and to improve the fit of the models. We used logistic regression models to estimate odds ratios of respiratory symptoms and/or asthma medication use with residential proximity to fumigant use. Our primary outcome was respiratory symptoms defined as positive if during the previous 12 months the mother reported for her child any respiratory symptoms or the use of asthma medications, even in the absence of such symptoms . We also examined asthma medication use alone. The continuous lung function measurements were approximately normally distributed,plastic potting pots therefore we used linear regression models to estimate the associations with residential proximity to fumigant use. We estimated the associations between the highest spirometric measures for children who had one, two or three maneuvers. We fit separate regression models for each combination of outcome, fumigant, time period, and buffer distance. We selected covariates a priori based on our previous studies of respiratory symptoms and respiratory function in this cohort. For logistic regression models of respiratory symptoms and asthma medication use, we included maternal smoking during pregnancy and signs of moderate or extensive mold noted at either home visit . We also included season of birth to control for other potential exposures that might play a causal role in respiratory disease , pollen , dryness , and mold. We defined the seasons of birth as follows: pollen , dry , mold based on measured pollen and mold counts during the years the children were born . In addition, we controlled for allergy using a proxy variable: runny nose without a cold in the previous 12 months reported at age 7. Because allergy could be on the causal pathway, we also re-ran all models without adjusting for allergy. Results were similar and therefore we only present models controlling for allergy. Additionally, for spirometry analyses only, we adjusted for the technician performing the test, and child’s age, sex and height. We included household food insecurity score during the previous 12 months , breastfeeding duration , and whether furry pets were in the home at the 7 year visit to control for other factors related to lung function. We also adjusted for mean daily particulate matter concentrations with aerodynamic diameter ≤ 2.5 µm during the first 3 months of life and whether the home was located ≤150m from a highway in first year of life determined using GIS, to control for air pollution exposures related to lung function. We calculated average PM2.5 concentration in the first 3 months of life using data from the Monterey Unified Air Pollution Control District air monitoring station.

In all lung function models of postnatal fumigant use, we included prenatal use of that fumigant as a confounder. To test for non-linearity, we used generalized additive models with three-degrees of-freedom cubic spline functions including all the covariates included in the final lung function models. None of the digression from linearity tests were significant ; therefore, we expressed fumigant use on the continuous log10 scale in multi-variable linear regression models. Regression coefficients represent the mean change in lung function for each 10-fold increase in wind-weighted fumigant use. We conducted sensitivity analyses to verify the robustness and consistency of our findings. We included other estimates of pesticide exposure in our models that have been related to respiratory symptoms or lung function in previous analyses of the CHAMACOS cohort. Specifically, we included child urinary concentrations of dialkylphosphate metabolites , a non-specific biomarker of organophosphate pesticide exposure using the area under the curve calculated from samples collected at 6-months, 1, 2, 3.5 and 5 years of age . We also included agricultural sulfur use within 1-km of residences during the year prior to lung function measurement . We used similar methods as described above for fumigants to calculate wind-weighted sulfur use, except with a 1-km buffer and the proportion of time that the wind blew from each of eight directions during the previous year. The inclusion of these two pesticide exposures reduced our study population with complete data for respiratory symptoms and lung function . Previous studies have observed an increased risk of respiratory symptoms and asthma with higher levels of p, p’– dichlorodiphenyltrichloroethylene or p, p’-dichlorodiphenyldichloro-ethylene measured in cord blood . As a sensitivity analysis, we included log10- transformed lipid-adjusted concentrations of DDT and DDE measured in prenatal maternal blood samples . We also used Poisson regression to calculate adjusted risk ratios for respiratory symptoms and asthma medication use for comparison with the ORs estimated using logistic regression because ORs can overestimate risk in cohort studies . In additional analyses of spirometry outcomes, we also excluded those children who reported using any prescribed medication for asthma, wheezing, or tightness in the chest during the last 12 months to investigate whether medication use may have altered spirometry results. We ran models including only those children with at least two acceptable reproducible maneuvers . We ran all models excluding outliers identified with studentized residuals greater than three. We assessed whether asthma medication or child allergies modified the relationship between lung function and fumigant use by creating interaction terms and running stratified models. To assess potential selection bias due to loss to follow-up, we ran regression models that included stabilized inverse probability weights . We determined the weights using multiple logistic regression with inclusion as the outcome and independent demographic variables as the predictors. Data were analyzed with Stata and R . We set statistical significance at p<0.05 for all analyses, but since we evaluated many combinations of outcomes, fumigants, distances and time periods we assessed adjustment for multiple comparisons using the Benjamini-Hochberg false discovery rate at p<0.05 . Most mothers were born in Mexico , below age 30 at time of delivery , and married or living as married at the time of study enrollment . Nearly all mothers did not smoke during pregnancy.