The pesticides, called pyrethroids (pie-REE-throids), have been considered safe for fish and other organisms that live in the water column, but no one has studied their effect on sediment-dwelling organisms, such as midge larvae or shrimp-like amphipods, said University of California, Berkeley, biologist Donald P. Weston, adjunct associate professor of integrative biology. These two organisms are used by the U.S. Environmental Protection Agency (EPA) as indicators of the health of fresh water sediment.

Weston and colleague Michael J. Lydy (LIE-dee) of Southern Illinois University (SIU) in Carbondale collected sediment samples from 42 rivers, creeks, sloughs and drainage ditches in California's Central Valley and exposed amphipods and midge larvae to the sediments for 10 days. Twenty-eight percent of the sediment samples (20 of 71) killed amphipods at an elevated rate, and in 68 percent of these sediments, the pyrethroids were at levels high enough to account for the deaths. Thus, while other pesticides may well have contributed to the amphipod deaths in some sediment samples, pyrethroids alone explain the toxicity in the vast majority of the sediment samples, Weston said.

"About one-fifth of our Central Valley sediment samples are toxic to a standard testing species due to a class of pesticides no one has tested for before, for which there are little data on their toxicology when sediment-bound, and which are being promoted as an alternative to the increasingly restricted organophosphate insecticides," he said.

The study by Weston, Lydy and post-doctoral researcher Jing You in the Department of Zoology at SIU appeared in the April 8 online version of the American Chemical Society's journal E
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Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
6-May-2004