National Water Quality Assessment Program: Eastern Iowa Basins

Pesticides in Air in the Mississippi River Valley: A Comparison Between 1995 and 2007

W.T. Foreman, US Geological Survey, National Water Quality Laboratory.

P.D. Capel, M.S. Majewski, S.J. Kalkhoff, R.H.Coupe, R.C. ReVello, US Geological Survey

Program abstracts for 32nd annual North American meeting of the Society of Environmental Toxicology and Chemistry,November 13-17, 2011 Boston MA.

Weekly-composite air samples were collected using a glass-fiber filter/polyurethane foam plug high-volume air sampler during the 1995 and 2007 April through September growing seasons at two agricultural locations in Iowa and Mississippi. Samples were analyzed by GC/MS using selected-ion monitoring for a variety of pesticides and degradates, 31 of which overlapped the two sampling periods. At least 26 compounds were detected during the growing season from each site in both years. The number of pesticides detected in more than 50% of the samples doubled for 2007 compared to 1995. Pesticide use patterns (amounts, crop types, application procedures), coupled with seasonal weather and atmospheric processes influence detection frequencies and aerial concentrations. For example, trifluralin was detected nearly 100% of the time at both sites during both years; likely because it is used on a variety of different corps and is incorporated into the soil prolonging its period of volatilization following initial application. Atrazine (and its primary degradate chloroisopropylamino-s-triazine; CIAT) and metolachlor, which are extensively applied at both locations, were detected at least 50% of the time at all sites during both years. The insecticide chlorpyrifos increased in detection frequency from about 38% to 95% at both sites in 2007 compared to 1995; its concentration was greater in 2007 than 1995 in Iowa, but was comparable between the two years in Mississippi. Similarly, the pyrethroid insecticide cis-permethrin was detected more frequently and had greater concentrations at both sites in 2007 compared to 1995 that likely is a result of replacement of some use-restricted or eliminated organophosphorus or carbamate insecticides. Some pesticides were detected frequently at one location (acetochlor at Iowa) but not the other, as predicted based on crop and pesticide usage differences. Five compounds were detected only in 1995 or 2007. Voluntary removal of cyanzine from the US marketplace and its subsequent cancellation of registered uses in December 1999 resulted in a reduction from at least a 25% detection frequency at both sites in 1995 to no detections in 2007 samples.

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