Publication Summary

This report presents second-year (2004) results in a three-year study to characterize pesticide concentrations in salmon-bearing surface waters. Thornton Creek in the Cedar-Sammamish watershed was chosen for an urban drainage evaluation. Marion Drain, Spring Creek, and Sulphur Creek Wasteway in the Lower Yakima watershed represented agricultural land-use patterns.

Concentrations of pesticides were generally low and close to analytical detection limits. In the agricultural basin, 2,4-dichlorophenylacetic acid (2,4-D) was the most commonly detected pesticide. Dichlobenil was most commonly detected in the urban watershed. Five pesticides -- azinphos-methyl, chlorpyrifos, diazinon, malathion, and 4,4′-DDE -- were above the numeric component of selected standards.

The Washington State Department of Agriculture (WSDA) and the Washington State Department of Ecology (Ecology) designed a three-year monitoring study to characterize pesticide concentrations in salmonid-bearing streams during the typical pesticide-use season. This report presents data from the second year, 2004, in the study.

Two index watersheds, representing urban and agricultural land-use patterns, were sampled from March through October 2004. Thornton Creek in the Cedar-Sammamish watershed was chosen as the urban drainage. Marion Drain, Spring Creek, and Sulphur Creek Wasteway in the Lower Yakima watershed were chosen as the agricultural drainage.

Five conventional water quality parameters -- discharge, temperature, pH, conductivity, and total suspended solids -- were measured to characterize water quality of the streams and to investigate pesticide fate and toxicity.

Concentrations of all pesticides were generally low and close to analytical detection limits. In the agricultural basin, 2,4-dichlorophenylacetic acid (2,4-D) was the most commonly detected pesticide. Dichlobenil was most commonly detected in the urban watershed.

Pesticide detections were compared to Washington State promulgated and EPA recommended aquatic life criteria. Detections were also compared to acute and chronic toxicological endpoints used for pesticide registration by the EPA, Office of Pesticide Programs, Environmental Fate and Effects Division.

Five pesticides -- azinphos-methyl, chlorpyrifos, diazinon, malathion, and 4,4′-DDE -- were above the numeric component of various standards, but the weekly sampling frequency of this study did not allow for assessment of the temporal component of these standards. A single detection of malathion (3.05 µg/L) approached the acute LC50 for rainbow trout (4 µg/L) in the Marion Drain.

Link to EIM data for User Study ID CBUR002