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From October 27, 2005                                                                                                           

Toxic Levels of Pyrethroids Found in California Urban Streams
(Beyond Pesticides, October 27, 2005)
Sediment from streams in Roseville, California has been found to contain levels of pyrethroids toxic to sediment dwelling organisms. On October 19th researchers from the University of California, Berkeley, Southern Illinois University and the Central Valley Regional Water Quality Control Board published their findings in the online issue of Environmental Science & Technology.

Synthetic pyrethroids have been on the market for over 20 years, and have been strongly pushed as a less harmful substitute for organophosphates. Pyrethroids are used on a variety of crops including cotton, fruits, and lettuce, as well as on residential lawns and homes. Pyrethroids are sometimes even combined with fertilizers.

While pyrethroids were at one time favored due to the fact that they bound with sediment, scientists and policy makers are now rethinking this supposed attribute. “The presumption was that if it binds to sediment, that substance becomes unavailable to organisms and, from a toxicity standpoint, irrelevant. And we're showing that not to be a fair assumption,” explains Donald Weston, adjunct professor of integrative biology at UC Berkeley and leader of the study. “If binding to sediment was a solution, we wouldn't be worried about DDT, we wouldn't be worried about PCBs, and we wouldn't be worried about a half dozen other organochlorine pesticides now banned.”

The organism that has been under observation is the amphipod Hyalella Aztec. Hyalella Aztec occurs naturally in creeks and streams in and around Roseville. The tests showed a correlation between high levels of pyrethroid toxicity in the sediment and the lack of wild amphipods. Amphipods were present in the main creek that had low levels of pyrethroids, while none were found in the tributaries, which contained high levels of pyrethroids in the sediment.

The study was a follow-up study to a prior study conducted in 2004, which focused on the presence of pyrethroids in creek sediment in agricultural areas. One of the most worrisome discoveries of this study is that what was once considered a problem that almost exclusively afflicted agricultural communities is now showing up in residential communities; proving that even common household use of pesticides is having an impact on the environment.

“Our work should be of broad public interest," observes Mr. Weston, "because the source of the toxicity we are finding in the creeks is just residential pesticide use in a typical suburban community. When people apply pesticides to their yards, or hire exterminators to do it, they just assume the pesticides will stay there. I think our work will increase awareness of the possible environmental dangers of pesticide overuse and maybe help people think twice before using pesticides 'just to be safe' when they do not have a clear pest problem.”

TAKE ACTION: Bring this information to the attention of local governments responsible for mosquito management. Make sure that it is known, through this example and others, that EPA registration of pesticide products does not ensure that products labeled for use and available in the marketplace are fully tested for impact on the environment and human health. This means that more effort and financial support needs to turn to prevention-oriented and source reduction programs that, in the case of mosquito management, control mosquitoes before they get to the adult stage. Also, look for alternatives ways to manage your pest problems on our Alternatives page, and find out how to have a healthy lawn without pesticides by visiting our Lawns page.