November 2016 Watershed Committee Presentation: Pesticides in Stormwater

Pesticides in Stormwater Runoff
Pose Risk to Aquatic Life

SWNI Watershed Committee Special Public Presentation
Everyone welcome!

Thursday, November 17, 2016

Multnomah Arts Center Room 30


A study by the U.S. Geological Survey Oregon Water Science Center found that commonly used pesticides, which enter streams via stormwater runoff, are impairing aquatic insects.  The results were published in May 2016 in the peer-reviewed Journal of Environmental Monitoring and Assessment.

The levels detected during a September 2013 storm in western Clackamas County exceeded U.S. Environmental Protection Agency benchmarks for protection of aquatic life. USGS staff analyzed samples of stormwater runoff, creek water, and bed sediments from 14 streams and five storm sewer outfalls for the presence of nearly 120 pesticides. All of the streams sampled had at least one chemical exceeding the benchmarks. The active ingredients of the insecticides detected included the chemicals bifenthrin, fipronil, malathion, and breakdown products of DDT - which has been banned for 44 years - among others.

The chemical appearing to cause the most toxicity was bifenthrin, a broad-spectrum insecticide used in over 600 retail products. Bifenthrin attaches tightly to sediments contained in stormwater, traveling from the areas where it was applied through storm drainage systems to streams. When even small amounts of this chemical are mobilized, beneficial insects may be affected when the sediments and associated chemical settle out in streams.

Streams with no or low levels of bifenthrin in their sediment had significantly more aquatic insects such as mayflies, caddisflies and stoneflies than streams with high concentrations of bifenthrin. Streams with high sediment levels contained mostly pollution-tolerant organisms, primarily non-insects. 

"Because aquatic insects provide food for fish, birds and other wildlife, it is critical to better understand the full impact from this insecticide, including whether it is entering the food chain," said Kurt Carpenter, USGS hydrologist and co-lead on the study. "The strong negative effect of bifenthrin on aquatic invertebrates seen in our study is consistent with national USGS findings that in urban streams, of the many contaminants examined, bifenthrin in bed sediments was the single best predictor of observed toxicity."

You can help protect bugs and keep pesticides out of our backyard streams!

  • Learn to identify, appreciate, and encourage native insects! or
  • Choose the least harmful options for care of your home, yard, and garden. Compare options at or call Metro's gardening and recycling information hotline, 503-234-3000.
  • Reduce sediment in runoff by covering areas of bare soil in your yard.  Contact the WRC at or 503-823-2862 for a list of native plants to help control erosion.
  • Clean driveways and sidewalks with a broom.
  • Choose landscapers that are certified. 
  • When pesticide use is necessary, follow label directions for application and disposal exactly. Avoid using pesticides on windy or rainy days or in irrigated areas. Hire a licensed professional pesticide applicator if possible.