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

Abstract

This 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.