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Pesticide No Panacea

Pyrethroids - a family of synthetic substances derived from toxins found in chrysanthemums - have won the lion's share of the residential insecticide market since more hazardous chemicals like diazinon and chlorpyrifos (Dursban) were phased out. But there's a catch: A recent study in Placer County suggests collateral damage to urban creek ecosystems. The apparent victims are tiny bottom-dwelling amphipod crustaceans called scuds (Hyalella azteca), a favored prey of small fish, tadpoles, newts, and aquatic insects.

U.C. Berkeley environmental toxicologist Donald Weston looked at pyrethroid levels and Hyalella populations in suburban Roseville's Kaseberg and Pleasant Grove creeks. The pyrethroids, primarily bifenthrin, cyfluthrin, and cypermethrin, in creek bed sediments killed scuds in laboratory tests. No living Hyalella were found in Kaseberg and the south branch of Pleasant Grove, the creeks with the highest pyrethroid levels. The scuds were only present in areas with the least residential influence.

"We are so used to thinking of pollution as coming from 'them,'" Weston told the Sacramento Bee. "But this is not the petrochemical plant. It's basic suburban pesticide use. The source is 'us,' not 'them.'" Pyrethroids are widely used in termite control, which often involves injecting the chemical underground. While underground injection is unlikely to be a problem for creeks, surface applications are washed from around buildings, lawns, and gardens into watersheds, where they bind with sediments.

"Diazinon and Dursban were causing widespread toxicity in water in urban creeks, and now we are getting widespread toxicity in sediment," says water-quality consultant Kelly Moran. "We really are not getting anywhere."

Pyrethroids have long been known to be highly toxic to fish, including coho salmon and rainbow trout. Trapped in creek sediments, the chemicals won't impact fish directly. But if they kill scuds and other benthic organisms, there's reason for concern about cascading effects through aquatic food webs.

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