PESTICIDES AND METABOLITES IN THE SHALLOW GROUNDWATER OF AN EASTERN COASTAL-PLAIN WATERSHED

The occurrence of pesticides in drinking water sources is a public con cern because of potential adverse health effects. We report the result s of a three-year study to assess the occurrence of pesticides and met abolites in shallow groundwater in a USDA Water Quality Demonstration Project(WQDP). The Herrings Marsh Run (HMR) watershed is located in th e eastern Coastal Plain region of North Carolina and has similar chara cteristics of other regional agricultural-intensive watersheds. Ninety -two shallow groundwater wells were installed on farms around the wate rshed in late 1992 and early 1993. Water samples were collected monthl y from March 1993 to March 1995 and collected quarterly for the remain der of 1995 and early 1996. The samples (n = 2598) were initially scre ened for II pesticides (8 triazines, 2 chloroactamides, I methylester) using immunoassay techniques. The positive detections (n = 266) were further analyzed by gas chromatographic (GC) and GC/MS (mass spectrome tric) procedures. During the study period we found that the majority ( 91%) of the wells had no detections for 11 compounds commonly used in the watershed Pesticides were consistently detected in four wells, but the concentrations were usually below the health advisory limit (HAL) . Overall, alachlor was the most frequently detected pesticide. The la ck of II commonly used pesticides in a high number of wells suggests t hat these pesticides have had a minimal impact on the quality of HMR s hallow groundwater.