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Sediments in many Central Valley streams contain toxic levels of pyrethroid pesticides

nvironmental Science & Technology and will be published later in hard copy.

In the tests, the midge larvae died at higher rates when exposed to sediment from 13 percent of 39 collection sites, and 40 percent of these sediment samples contained enough pyrethroids to account for the deaths. Weston notes that these midges (Chironomus tentans) are known to be about three times less sensitive to pyrethroids than are the amphipods (Hyalella azteca), which explains the difference between the species results.

"Since the levels are high enough to be toxic to the standard 'lab rat' species, the next question is: What's happening with the resident species?" Weston said. "The concern is that invertebrates, particularly crustaceans, could have reduced populations, and these organisms are an important food for a variety of bottom-feeding fish."

Alternatively, the amphipods and midge larvae from areas of intensive agricultural or urban pesticide use may have adapted to live with normally toxic levels of the pesticide. Weston and his colleagues now are sampling these organisms from the rivers, creeks, sloughs and ditches to determine if they respond the same way as lab-raised organisms.

Pyrethroids are a class of compounds represented by permethrin, first marketed in 1973, and various other chemicals usually ending in the suffix -thrin. Permethrin is found in home and garden pesticides ranging from RAID to flea killers and head lice creams, but permethrin and it's kin find broad use in agriculture, such as on cotton, fruit and nut orchards, and on lettuce and rice. California's Central Valley produces more than half the nation's fruits, vegetables and nuts.

Though pyrethroids are used far less than organophosphates like diazinon and chlorpyrifos, their use in California has risen rapidly in recent years because of increased regulation of the spraying of organophosphates, due to health threats to farm workers and increased toxic runoff from fi
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Contact: Robert Sanders
rls@pa.urel.berkeley.edu
510-643-6998
University of California - Berkeley
6-May-2004


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