U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting Charleston South Carolina March 8-12,1999--Volume 2 of 3--Contamination of Hydrologic Systems and Related Ecosystems, Water-Resources Investigation Report 99-4018B

Herbicides and their Metabolites in Cayuga Lake and its Tributaries, New York

by David A.V. Eckhardt, William M. Kappel, William F. Coon, and Patrick J. Phillips

This report is available in pdf format: Eckhardt .pdf

ABSTRACT

Analyses of stormflow samples collected from tributaries to Cayuga Lake in western New York shortly after application of atrazine and metolachlor to agricultural fields in June 1998 indicate that the highest concentrations, and the bulk of the loads of the two herbicides in the three tributaries was transported during peak flows. Concentrations of metolachlor metabolites remained high after the flow peaked as the soils drained. In contrast, deethylatrazine concentrations, which were generally low, increased only slightly during stormflow, apparently because the parent compound (atrazine) degrades at a much slower rate than metolachlor. Far more metolachlor-ESA (a degradation compound) was transported than any other pesticide or degradate; this indicates that it is relatively stable and mobile in the hydrologic environment. The ratios of a metabolite concentration to that of other metabolites and the parent compound in stream-water samples showed that base flow in the tributaries before the storm was enriched with metolachlor-ESA, but not with metolachlor or metolachlor-OA. After the storm, the ratio of metolachlor-OA to metolachlor increased markedly in the base flow; apparently metolachlor-OA that is formed in soils after pesticide application is readily leached but does not persist in ground water as much as metolachlor-ESA does. Water samples taken from Cayuga Lake in July, after the early-summer flush of pesticide residues in June, indicated fairly uniform concentrations of herbicides throughout the lake --from 0.2 to 0.6 µg/L for atrazine and from 0.05 to 0.3 µg/L for metolachlor. The ratios of the three metabolites to their parent compounds were significantly higher in lake water than in the three tributaries, possibly as a result of (1) the inflow of ground water that enters the lake directly from adjacent agricultural land, and (2) the transformation of the parent compounds during their residence in the lake.