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 Investigations Report 99-4018B

Degradation Rates of Six Pesticides in Water from the Sacramento River, California

By Keith Starner, Kathryn M. Kuivila, Bryan Jennings, and G. Edward Moon

This paper is available in pdf format: CA-0216.pdf

ABSTRACT

The degradation rates of six pesticides were measured in water samples collected from the Sacramento River, California, in April and August 1996. Samples were spiked with the pesticides carbaryl, malathion, atrazine, simazine, methidathion, and diazinon, and the concentrations were measured at various intervals. The laboratory experiments were done in the dark in incubators at 10°C to 25°C to represent a range of conditions. Carbaryl and malathion degraded rapidly, with half lives of 2-3 weeks at 10°C and of 1-5 days at 25°C. In contrast, atrazine and simazine were stable under all conditions. For methidathion and diazinon, the degradation rates were quite variable, with half lives ranging from 9 days to no observed degradation during the 34-37 days of the experiment. Differences between the water collected in April and August were more important than temperature in controlling the degradation rates of methidathion and diazinon. A more complete understanding of the factors that control this variability is necessary for accurate modeling of environmental fate.