MONITORING GROUNDWATER FOR PESTICIDES AT SELECTED MIXING LOADING SITES IN ARKANSAS/

Groundwater monitoring studies have been conducted in recent years to survey contamination due to pesticides, yet few have addressed wells w here pesticides are mixed, loaded, or rinsed. Beginning in 1990, a mon itoring study conducted over a 2-year period included five collections at each of 16 mixer/loader locations to assess any pesticide and nitr ate contamination. At sites in 11 counties, samples for pesticide anal ysis were extracted with solid-phase extraction (SPE) disks. Samples w ere screened using gas chromatography-electron capture detection (ECD) and high-performance liquid chromatography-UV detection (LCUV) for 17 pesticides commonly used in Arkansas. Detections were confirmed by ga s chromatography-mass spectroscopy (MS) or co-chromatography. Fourteen samples revealed atrazine (1 detection), cyanazine (4), parathion-met hyl (2), metolachlor (2), norflurazon (1), pendimethalin (1), propanil (2), or trifluralin (1) at eight locations during the 2-year study. T wo detections of parathion-methyl and one detection of trifluralin wer e above the Lifetime Health Advisory Level (LHAL) of 2 mu g L(-1). Dat a suggested a high correlation between pesticide used and pesticide de tected at sites sampled. Three wells contained NO3-N concentrations of 10 mg L(-1) or higher, but these did not correlate with pesticide con centrations. The pesticide's proximity to the wells during mixing, rin sing, or loading was considered to be a greater influence on temporary contamination of groundwater than chemical or site-specific character istics.