Children\u27s Inhalation Exposure to Methamidophos from Sprayed Potato Fields in Washington State: Exploring the Use of Probabilistic Modeling of Meteorological Data in Exposure Assessment

We examined the significance of meteorology and postspray volatilization of methamidophos (an organophosphorus insecticide) in assessing potential inhalation risk to children in an agricultural community. We combined fluxes from sources and dispersion modeling with a range of possible local meteorology to create output to study the variability in potential community exposure as a result of changing temperature, wind speeds and wind directions. This work is based on an aerial spray drift study where air sampling measurements of methamidophos were made before, during and after a spray event were used to examine acute inhalation risk for children living in an Eastern Washington State community in close proximity (between 15 and 200 m) to sprayed potato fields. We compared the measured average air concentrations of methamidophos in the community to a “no observed adverse effect level” for subchronic inhalation to characterize acute and subchronic inhalation risks. The baseline estimates of inhalation exposure were below Environment Protection Agency\u27s (EPA) level of concern based on a target margin of exposure of 300. As meteorological conditions during and after spraying influence the amount of material moving into areas where children reside we used historical meteorological data to drive model simulations that predicted likely air residue concentrations under different wind and temperature conditions. We also added variability to the decay constant and initial emission fluxes to create a 2-D simulation of estimated air concentrations in the community near the fields. This work provides a methodological framework for the assessment of air concentrations of pesticides from agricultural sprays in the absence of extended measurements, although including variability from meteorological conditions. The deterministic as well as the probabilistic risk analyses in this study indicated that postspray volatilization in the specific spray situation analyzed (methamidophos applied on potato fields in Eastern Washington) did not pose acute or subchronic risks as defined by the EPA. However, this study did not consider any pathway of exposure other than inhalation (e.g. diet, dermal, etc.) and the risk assessment should be evaluated in that context

Risk of Childhood Cancers Associated with Residence in Agriculturally Intense Areas in the United States

Background: The potential for widespread exposure to agricultural pesticides through drift during application raises concerns about possible health effects to exposed children living in areas of high agricultural activity. Objectives: We evaluated whether residence in a county with greater agricultural activity was associated with risk of developing cancer in children \u3c 15 years of age. Methods: Incidence data for U.S. children 0–14 years of age diagnosed with cancer between 1995 and 2001 were provided by member registries of the North American Association of Central Cancer Registries. We determined percent cropland for each county using agricultural census data, and used the overall study distribution to classify agriculturally intense counties. We estimated odds ratios and 95% confidence intervals for all ages and 5-year age groups for total cancers and selected cancer sites using logistic regression. Results: Our study results showed statistically significant increased risk estimates for many types of childhood cancers associated with residence at diagnosis in counties having a moderate to high level of agricultural activity, with a remarkably consistent dose–response effect seen for counties having ≥ 60% of the total county acreage devoted to farming. Risk for different cancers varied by type of crop. Conclusions: Although interpretation is limited by the ecologic design, in this study we were able to evaluate rarer childhood cancers across a diverse agricultural topography. The findings of this exploratory study support a continued interest in the possible impact of long-term, low-level pesticide exposure in communities located in agriculturally intense areas

Global positioning system (GPS) tracking to characterize children's exposure to pesticides

Thesis (Ph. D.)--University of Washington, 2004This dissertation documents the dynamic interaction between moving human receptors (children) and transient peaks in drifted pesticides proximal to treated fields. Validation of a novel dGPS instrument (the GPS Personal Acquisition Logger or GPS-PAL) to attain high-resolution time-location data required four tests: amenability, reception, resolution, and interference. Children were amenable to the GPS-PAL worn in a vest. Lack of reception limited the GPS-PAL inside concrete and metal framed buildings, though time of entry and exit are known. Resolution was 3.2 m RMS. Interferences were 'opaque' buildings constructed of concrete and steel, and high electromagnetic frequency emitters.The GPS-PAL afforded greater resolution than an existing method, the National Human Exposure Assessment Study (NHEXAS) diary timeline, and showed in which categories subjects were likely to err. Low literacy (both English and Spanish) obstructed completion of the diary, but did not affect GPS-PAL compliance. GPS eliminates the need to categorize time-location data.GPS data were collected for 8 children during and after aerial spraying of methamidophos on potato fields surrounding their community in Eastern Washington State. Children were active (from velocity data) and outside both days. Drift of most pesticide mass was short-range. Morning deposition was highest. Evening air concentration was highest, suggesting contribution of volatilization. Temperatures exceeded 40C in late afternoon. No deposited methamidophos was found indoors. Indoor air concentrations were not significantly different from baseline. Children's handwipe residues were detectable but low.Models were calibrated from environmental samples. By combining model and GPS data, attributable fraction of dermal and inhalation routes was characterized. Using a transfer factor of 400 cm2/hr, dermal exposure was predicted much higher than inhalation. However, methamidophos absorbs almost completely in lungs, while ∼5% absorbs from skin. Ingestion exposure was not measured. The GPS+Model method predicted mean inhaled exposure 3.5 times higher and mean dermal exposure 181 times higher than a 'standard' method. The utility of GPS tracking and modeling for capturing transience of drift in relation to hyperkinetic movement of moving children was well demonstrated. The potential of GPS tracking for exposure assessment is documented by this dissertation