The new study is the first published work to document toxic levels in the water column as well as in the sediments at the bottom of streams.
"This work opens a whole new can of worms and will probably substantially expand that re-evaluation," Weston said.
Weston's study, conducted with Michael J. Lydy (LIE-dee) of SIU in Carbondale and funded by the Surface Water Ambient Monitoring Program of the California Environmental Protection Agency, appears online today (Tuesday, Feb. 2) in the journal Environmental Science & Technology.
Pyrethroids have been around for decades, but seldom were used until organophosphates like chlorpyrifos and diazinon were banned for homeowner use in 2001 and 2004, respectively. Since then, pyrethroid insecticide use has skyrocketed, while studies in urban streams have found levels toxic to sensitive "indicator" species in California's Central Valley as well as in Texas and Illinois. The crustacean Hyalella azteca, for example, is paralyzed and killed at levels of 2 parts per trillion.
The main sources appear to be readily available insecticides applied around the home by the homeowner or by professional pest control firms to control pesky ants, Weston said. Of the varieties of pyrethroids marketed, however, one bifenthrin was found most often in the rivers and creeks in the Sacramento area, and pest control companies in California use four times as much as homeowners do, he said.
He noted that in some areas, pest control companies heavily market monthly or bimonthly sprayings outside the home to control ants.
"I question whether most people need routine insecticide treatment of their property, which results in residues on the lawn, in the garden and around the house that, when it rains, go down the storm drains and out into the creeks and rivers," Weston said. "Average homeowners, when they hire pest control companies to regularly spray th
|Contact: Robert Sanders|
University of California - Berkeley