Alarmed that popular insecticides that end up in urban streams are killing tiny aquatic creatures, California's pesticide agency is conducting a review that is likely to lead to restrictions on many products used on lawns and gardens.
The chemicals, pyrethroids, are man-made versions of natural compounds in chrysanthemum flowers. Their use has skyrocketed in the past few years as U.S. consumers and exterminators search for less-toxic alternatives for dangerous insecticides already banned.
But last fall, a UC Berkeley scientist reported that pyrethroids are polluting streams in Northern California suburbs, wiping out crustaceans and insects vital to ecosystems.
Mary-Ann Warmerdam, director of the state Department of Pesticide Regulation, said Thursday that notices will be sent next month to manufacturers of about 600 pyrethroid products informing them that the state is reevaluating their use. That kicks off a process that will probably culminate in new regulations, and perhaps bans of some products in California.
"We've got the caution flag out," Warmerdam said. "This is a shot across the bow to the manufacturers that we found a reason for concern and you need to provide us with data to either eliminate the concern, reformulate your products or consider taking them off the market."
Allan Noe, a spokesman for CropLife America, representing pesticide manufacturers, said Thursday that the companies were unaware of California's intentions but will cooperate with its requests. He said the industry does not agree that there are toxicity problems but is analyzing the way the products are used.
"The valuable contributions that pyrethroids make through agricultural and urban uses are many and these benefits need to be considered," Noe said.
The compounds, particularly one called permethrin, are prevalent in lawn products and household and pet sprays, as well as in insecticides sprayed by exterminators and farmers. Also, many cities and counties spray a pyrethroid for mosquito control to prevent the spread of West Nile virus.
Although they poison nerve cells of invertebrates, the compounds are among the least toxic insecticides for humans and other mammals as well as birds. That is why they have replaced the organophosphate insecticides diazinon and chlorpyrifos, which were phased out by the EPA because they are particularly hazardous for children.
Use of pyrethroids by California farmers and exterminators has nearly tripled, growing from about 420,000 pounds in 1999 to 1.1 million pounds in 2004. Consumers' retail sales are not included in those numbers but state officials say their usage probably doubles that volume.
Donald Weston, an adjunct professor of integrative biology at UC Berkeley, said his studies have shown that pyrethroids are flowing into storm drains and building up to toxic levels in stream sediment.
Creeks in the Sacramento suburb of Roseville that contain high pyrethroid levels are devoid of tiny crustaceans called hyalella, while nearby streams with low levels are inhabited by them, according to Weston's study, published in October. In lab tests, nearly all samples of the pesticide-tainted sediments from the creeks killed the creatures.
The creatures -- shrimp-like amphipods that live in bottom sediment -- are important prey for small fish, frogs, salamanders and aquatic insects. Their presence is often considered a sign of a healthy waterway.
Weston said that the most toxic compound in the creeks is bifenthrin, which is sprayed around houses by exterminators and is found in some consumer products that are spread on lawns. He did not find pyrethroids from farms or mosquito control in the creeks.
About 20% of the Central Valley's streams contain pyrethroid levels that are toxic to the crustaceans. In addition, they have been detected in creeks in the Monterey area and the Imperial Valley. No tests have been done in the Los Angeles region.
Glenn Brank, a spokesman for the state pesticide department, called the targeting of pyrethroids "definitely the biggest regulatory initiative ever in California involving pesticides and surface waters."
"It will be the kickoff for regulatory oversight for years to come," he said.
In restricting pyrethroids, however, the state agency hopes to keep some as options and ensure that people don't switch to products that wind up being worse.
"We want to do our best to maintain these materials and their viability. They are relatively safe. They don't pose a human health problem like these other materials do," Warmerdam said.
The EPA is also reviewing pyrethroids for possible national restrictions.
Consumers can identify pyrethroids in products by checking labels for compounds that end in "thrin." They are broad spectrum insecticides effective against a wide variety of flying and crawling insects.
State officials said they will be particularly careful in restricting any pyrethroids sprayed by vector control agencies, since combating the West Nile virus, which is spread by mosquitoes, is important.
When manufacturers receive the state notices next month, they must agree within 60 days to begin gathering information about their products' toxicity and buildup in waterways. If they refuse, the agency will immediately cancel their products and they cannot be sold in California.
Labels required by the EPA define how much should be used and prohibit application within 100 feet of waterways. But Warmerdam said the current warnings may be insufficient because consumers now use large volumes.
"The problem is not the material itself. The real challenge is trying to address what appears to be misuse and misapplication ... We may have to eliminate products altogether" or require them in different forms less prone to runoff, she said.