Contributions of nearby agricultural insecticide applications to indoor residential exposures

Abstract

Background: Pesticide exposure has been associated with adverse health effects. We evaluated relationships between proximity to agricultural insecticide applications and insecticides in household dust, accounting for land use and wind direction.

Methods: We measured concentrations (ng/g) of nine insecticides in carpet-dust samples collected from 598 California homes. Using a geographic information system (GIS), we integrated the California Pesticide Use Reporting (CPUR) database to estimate agricultural use within residential buffers with radii of 0.5 to 4 km. We calculated the density of use (kg/km²) during 30-, 60-, 180-, and 365-day periods prior to dust collection and evaluated relationships between three density metrics (CPUR unit-based, agricultural land area adjusted, and average daily wind direction adjusted) and dust concentrations. We modeled natural-log transformed concentrations using Tobit regression for carbaryl, chlorpyrifos, cypermethrin, diazinon, and permethrin. Odds of detection were modeled with logistic regression for azinphos-methyl, cyfluthrin, malathion, and phosmet. We adjusted for season, year, occupation, and home/garden uses.

Results: Chlorpyrifos use within 1-4 km was associated with 1 to 2-times higher dust concentrations in both the 60- and 365-day periods. Carbaryl applications within 2-4 km of homes 60-days prior to dust collection were associated with 3 to 7-times higher concentrations and the 4 km trend was strongest using the wind-adjusted metric (p-trend = 0.04). For diazinon, there were 2-times higher concentrations for the 60-day metrics in the 2 km buffer and for the CPUR and wind-adjusted metrics within 4 km. Cyfluthrin, phosmet, and azinphos-methyl applications within 4 km in the prior 365-days were associated with 2-, 6-, and 3-fold higher odds of detection, respectively.

Conclusions: Agricultural use of six of the nine insecticides within 4 km is an important determinant of indoor contamination. Our findings demonstrated that GIS-based metrics for quantifying potential exposure to fugitive emissions from agriculture should incorporate tailored distances and time periods and support wind-adjustment for some, but not all insecticides.

Keywords: Environmental epidemiology, Dust, Agriculture; Exposure assessment; Insecticides; Pesticides.

Figure 1.

Illustration of the CPUR density metric for the 1km and 4km buffer around the residence on one day for four application sites. In the 1km buffer, one application of chlorpyrifos is included after weighting the 6.0 kg applied by 12% due to most of the public land survey section (PLSS) being outside of the buffer. In the 4km buffer, three applications of chlorpyrifos are included in entirety and one application is weighted by 70% due to 30% of the PLSS being outside of the buffer.

Figure 2.

Illustration of the CROP-A metric for the 1km and 4km buffer around the residence on one day for four application sites. The applications of chlorpyrifos are matched to the acres of pasture/hay and cultivated crops identified in each public land survey section (PLSS) within the buffer. The metric is refined by weighting the amount of chlorpyrifos applied by the proportion of pasture/hay and cultivated crops (i.e., agricultural land) identified in each PLSS within the buffer.

Figure 3.

Illustration of the W-CPUR metric within a 4km buffer around the residence on one day for four application sites. The wind direction is determined for each day between application and dust collection for each public land survey section (PLSS) centroid with a chlorpyrifos application within the buffer to calculate the proportion of days the home was downwind of the application site.

Figure 4.

Distributions of carbaryl, chlorpyrifos, diazinon, and cypermethrin concentrations in house dust of homes with (Yes) and without (No) nearby agricultural use in the prior 365 days Yes=Homes with CPUR applications (exposed); No=Homes without CPUR applications (unexposed); p-values from Wilcoxon rank sum test used to compare the distribution of the insecticide concentration in the dust among homes classified as exposed and those classified as unexposed; dust concentrations with values 1.5 times the IQR above the upper quartile or below the lower quartile were excluded from the graphs.