Pyrethroids, among the most widely-used home pesticides, are winding up in California rivers at levels toxic to some stream-dwellers, possibly endangering the food supply of fish and other aquatic animals, according to a new study by researchers at the University of California, Berkeley, and Southern Illinois University (SIU).
Pyrethroid insecticides, commonly used in California to kill ants and other insect pests around the home, have been found in street runoff and in the outflow from sewage treatment plants in the Sacramento area. The insecticide ended up in two urban creeks, the San Joaquin River and a 20-mile stretch of the American River, traditionally considered to be one of the cleanest rivers in the region.
Although the pyrethroid levels were low around 10-20 parts per trillion they were high enough to kill a test organism similar to a small shrimp that is used to assess water safety.
"These indicator organisms are 'lab rat' species that are very sensitive, but if you find something that is toxic to them, it should be a red flag that there could be potential toxicity to resident organisms in the stream," said study leader Donald P. Weston, UC Berkeley adjunct professor of integrative biology.
Fish would not be affected by such low levels, Weston said, but aquatic larvae that the fish eat, such as the larvae of mayflies, stoneflies and caddisflies, could be, and should be studied.
Weston first began looking at pyrethroid levels in streams bordering farm fields in 2004, and reported levels in some creek sediments high enough to kill the shrimp-like amphipod, an organism used by the U.S. Environmental Protection Agency as an indicator of the health of freshwater sediment. He subsequently found even higher pyrethroid levels in the sediments of urban streams, contributing to the California Department of Pesticide Regulation's decision in August 2006 to re-evaluate some 600 pyrethroid products on the market, a p
|Contact: Robert Sanders|
University of California - Berkeley