Pesticide Transport in Shallow Groundwater

Abstract

ABSTRACT TO meet increasing demands for data on pesticide transport to groundwater, residues of selected pesticides, EDB, atrazine, butylate, aldicarb, and fenamiphos were monitored in shallow groundwater beneath a Bonifay sand in the southeast Coastal Plain near Tiftaon, GA. Pesticides in tile outflow from the treated area were also monitored along with pesticide residue in soil. Low concentrations of atrazine and butylate were present in wells at depths of 1.0 m, L5 m, and 2.4 m beginning with the second year (1984) of the study. Fenamiphos was detected in only one well throughout the study. However, EDB and aldicarb moved readily to groundwater and in the tile outflow. Results were generally as would be predicted considering chemical properties of the pesticides. However, in these studies we found that aldicarb was very rapidly converted to the sulfone derivative which was the dominant species in well water and tile outflow. Some researchers have found aldicarb sulfoxide to be the dominant metabolite in soils. Others have also found fenamiphos to be transformed to a persistent sulfoxide form which is mobile in soil. Since we found little fenamiphos or its metabolites in groundwater and tile outflow, we speculate that degradation occurs rapidly in our soils. Fenamiphos translocation observed in soil suggested the presence of the more mobile metabolites in soil. Masses of pesticide transported from the treated area were computed using concentrations and estimated water budgets. Comparing leaching losses from the root zone estimated using GLEAMS simulation with groundwater transport shows that <10% of the leaching losses were actually transported from the treated area in shallow groundwater during the observation period. The difference evidently remained in storage or was adsorbed or degraded in transport.