A family of pesticides used increasingly nationwide in place of more heavily restricted organophosphate pesticides has accumulated in many creek sediments to levels that are toxic to freshwater bottom dwellers, according to a new study.
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 Californias 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.
Robert Sanders | EurekAlert!
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