Pyrethroids are a group of synthetic insecticides, commonly used in residential areas in the United States. Their use has increased during the past decade, as use of organophosphate pesticides has declined. While not as acutely toxic to birds and mammals, pyrethroids are relatively toxic to insects and aquatic invertebrates. The elevated residential and commercial use of pyrethroids has resulted in an increased detection of these compounds in urban runoff, potentially exposing aquatic life to harmful levels in urban streams.

This data report summarizes the results of a pyrethroid survey in sediments collected in October 2014 from six King County streams (Juanita and Forbes Creeks in Bothell, Thornton and Piper’s creeks in north Seattle, and Springbrook and Mill creeks in Renton/Kent/Auburn). The following study questions are addressed: 

1) What is the range of current sediment pyrethroid concentrations in six King County streams during the early wet season? 

2) What is the variability in early wet season pyrethroid concentrations in stream sediments within stream basins? 

3) Are stream sediments in these streams toxic to H. azteca and are pyrethroids contributing to the toxicity? 

4) Are pyrethroids widespread in King County streams at levels of ecological concern?