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Lonna Frans,
USGS Hydrologist,
934 Broadway,
Suite 300
Tacoma, WA 98402

(253) 552-1694
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Urban Pesticide

Project Summaries

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9722-9F3 - Pesticide Toxicity in Urban Streams, King County, Washington - Completed FY2004

Introduction - A 1998 study conducted by the U.S. Geological Survey Puget Sound Basin NAWQA team, the Washington State Department of Ecology (WDOE), and King County found that insecticides in 9 of 10 sampled urban streams exceeded criteria for the protection of aquatic life. Water samples from one of the sites was found toxic to Ceriodaphnia dubia, a nearly microscopic animal, and Selenastrum capricornutum, a microscopic plant. This proposed study is the next step in determining if toxicity is typical in urban streams in King County, and if so, what are the likely causes.


  1. Determine if the toxicity observed in the 1998 study is typical in urban and suburban streams in King County.
  2. Assess how toxicity of urban stream water varies seasonally.
  3. Assess the probable cause of the toxicity.
  4. Make recommendations for future studies.

Relevance and Benefits - A USGS fact sheet (Bortleson and Davis, 1997) documenting detections and concentrations of pesticides in small streams in the Puget Sound Basin reported that more pesticides were found in urban streams than in agricultural streams. The need to further investigate the presence and concentrations of pesticides in urban streams resulted in the 1998 study described in the introduction of this summary. The present study builds on the 1998 study by answering questions about the extent, and possibly the cause, of toxicity of urban streams in King County. Little is known about the toxicity of urban stream water in the Puget Sound Basin. Understanding the extent and cause of toxicity in urban streams is one of many factors that must be addressed if salmon runs are to be restored in the Pacific Northwest. The project is part of a larger role the USGS will play in helping to adddress salmon issues in the region.

Approach - Water samples collected from selected urban streams will be tested for toxicity to Ceriodaphnia and Selenastrum and analyzed for pesticides and metals.

  1. To assess seasonal variations in toxicity, samples will be collected during periods of storm runoff and during summer base flows.
  2. The cause of toxicity, if found, will be inferred by comparing results of toxicity tests to concentrations of pesticides, base-neutral and acid extractable
  3. organic compounds (BNAs), and metals in samples collected concurrently with the toxicity sample.

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