Monitoring for aldicarb residues in ground water of the Central Valley of California

Groundwater samples were collected in September 1989, September and October 1990, and December 1991 in the Central Valley of California and analyzed for aldicarb residues. Prior to each groundwater survey, statewide pesticide-use was determined. All water samples were analyzed by high-performance liquid chromatography. In the nine counties sampled, no residues of aldicarb, aldicarb sulfoxide, or aldicarb sulfone were detected. These results were surprising, due to the relatively high amounts of aldicarb applied in these counties. This may be due to the fact that the majority of combined applications to cotton and sugar beets is made between April and June, when most of the year's rainfall is completed. The shallow placement of aldicarb may also reduce the potential for leaching.