Keith S. Porter

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.

measurement of aldicarb degradation and movement in upstate New York and Massachusetts potato fields (U.S.A.)

Abstract The degradation and movement of aldicarb residues from an emergence application was measured in soil and groundwater beneath potato fields near Deerfield, Massachusetts, and Savannah, New York. Soil samples collected following the application showed that aldicarb residues degraded at a rate corresponding to a half-life of ∼1.1 months. This half-life is consistent with previous studies. At the Massachusetts location, residues in half of the plot were confined to the upper 1.2 m of soil. In the other half of the plot which was temporarily flooded due to an overflow of a nearby pond, residue movement exceeded 4.8 m and residues up to 21 μg L −1 were observed in the upper 1.5 m of the saturated zone. No residues were observed in wells installed farther than 40 m from the treated area and residues in all wells dropped below 10 μg L −1 within 16 months of the aldicarb application. At the New York site, aldicarb residues entered shallow groundwater after a period of heavy rainfall in late November and early December of 1986. During the study, aldicarb residues were confined to shallow groundwater directly beneath or within 5 m of the treatment area. Aldicarb residues in excess of 10 μg L −1 were not found deeper than ∼2.5 m below the water table. Aldicarb residues had declined to below 1 μg L −1 in all monitoring wells within 5 yr, implying an average half-life of aldicarb residues in groundwater of

Enhancing Risk Management by Focusing on the Local Level: An Integrated Approach

An integrated approach to risk management that focuses on the local level will lead to a more satisfactory and timely resolution of localized risk situations such as chemical contamination of groundwater that serves as a source of drinking water. More importantly this approach will result in additional positive long-range effects — increased local capabilities to deal with future chemical risk problems and improved prevention of some types of chemical contamination of groundwater. Conceptualizing the management of risks as having inputs (the risk situation, laws and policies, technical context, and community context), process, and outcomes illustrates that neither outside intervenors nor the local community should approach a risk situation without regard for all of the inputs or without understanding the dynamics of the process of managing risks at the local level.