From: Andy Soos, ENN
Published February 3, 2010 01:34 PM

Pesticides in California Rivers

Pyrethroids, which are 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.

A pyrethroid is a synthetic chemical compound similar to the natural chemical pyrethrins produced by certain flowers (such as Chrysanthemum). Pyrethroids now constitute a major proportion of the synthetic insecticide market and are common in commercial products such as household insecticides. In the concentrations used in such products, they may also have insect repellent properties and are generally harmless to human beings but can harm sensitive individuals.


Pyrethrins are low in toxicity to mammals because they are quickly broken down into inactive forms and pass from the body in the urine and feces. Pyrethrins are rapidly degraded in sunlight at the soil surface and water.  Pyrethrins have a soil half life of about 12 days and they tend to bind tightly to the soil.

Pyrethroid insecticides have been found recently in street runoff and in the outflow from sewage treatment plants in the Sacramento, California area. The insecticide ended up in two urban creeks, the San Joaquin River and a 20 mile stretch of the American River, which is 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, University of California Berkeley adjunct professor of integrative biology.

Fish are not likely to 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 for their potential effects on the ecosystem.

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