USGS logo

USGS Fact Sheet 067-97:
Pesticides in Selected Small Streams
in the Puget Sound Basin, 1987-1995

[Back] [Return to Front Page] [Next]

Factors Influencing Pesticide Concentrations and Detections

Detections and concentrations of pesticides in streams are influenced by many factors, including the amount of pesticide used, the environmental persistence of the pesticide, and the analytical methods used. In the Puget Sound Basin, the most commonly detected pesticides were among the most heavily applied. Eleven of the 18 pesticides that are most heavily used were detected in water or bed sediments (see table below). Application practices in urban and agricultural areas are important in determining whether pesticides reach streams. Pesticides are used around urban households, businesses, and parks, and application practices of urban users differ widely. Urban use of pesticides (about 1.1 million pounds/year) was more than three times greater than agricultural use (Tetra Tech, 1988). This may explain in part why the number of different pesticides found in urban streams is greater than in agricultural streams.

Chemical characteristics of pesticides are a major factor in environmental persistence. The majority of currently used pesticides break down relatively rapidly after application. Consequently, pesticide detections occur most frequently in the weeks following periods of heaviest pesticide application, which usually are in spring and early summer in the basin. Detections of pesticides have also increased over time as analytical methods improve and smaller concentrations can be measured.

[Table of pesticides commonly used in the Puget Sound Basin]
Click here for a table of commonly used
pesticides in the Puget Sound Basin

[Back] [Return to Front Page] [Next]

Puget Sound Basin NAWQA home page is <>
This page is http:// /pubs/fs/fs067/pest.e.html
Last modified: Mon Jun 9 17:25:40 1997
If you have any questions or comments about this document, contact <>.