Changing aldicarb residue levels in soil and groundwater, eastern Long Island, New York

Abstract

A study that involved repeated groundwater and soil-core sampling in four representative potato-growing areas of Long Island, New York was carried out between 1980 and 1984 to investigate the impact of the pesticide aldicarb on groundwater quality. Aldicarb residue concentrations in both the saturated and unsaturated zones were analyzed together with hydrologic data from the study sites. Results showed that the timing of initial residue delivery to groundwater was dependent on water-table depth. After arrival at the saturated zone, the rate of residue advance within the aquifer depended on the rate of groundwater movement, which is strongly associated in this area with location relative to regional groundwater divides. Residue concentrations in groundwater peaked earliest and highest in areas closest to the aldicarb application sites and later and lower in areas farther downgradient. Based on the observed patterns of residue distribution, the impact of the pesticide on the aquifer as a whole will be shorter in duration than some previous estimates. The continuing processes of groundwater flow, residue degradation, and dispersion will drop aldicarb residue concentrations in groundwater to below the New York State drinking-water guideline of 7 μg/L long before the associated groundwater leaves the aquifer through natural discharge.