The other shoe has dropped on a growing controversy over the use of a particular pesticide. It's one that has been used safely and effectively to control a wide array of urban and agricultural pests in California for more than 30 years because it has been discovered on streambed sediments.

As expected, the California Department of Pesticide Regulation has ordered more than 120 makers and sellers of pyrethroid pesticides to provide information to help DPR assess pesticide impact on waterways and prevent environmental harm.

Whatever ruling DPR makes will literally affect all 36 million Californians. It is not just an agricultural issue.

Pyrethroid pesticides are widely used to control major urban and agricultural pests from mosquitoes harboring West Nile Virus; lawn and garden products; household and commercial pest control products; structural pest control; livestock parasites; dog and cat flea collars; and pet shampoos.

Synthetic pyrethroids are man-made versions of pyrethrum, a natural insecticide produced by chrysanthemum flowers. Synthetic pyrethroids have been use since the 1970s in agriculture and for more than 20 years in consumer products.

Pyrethrum powder has been used since the mid-ninetieth century.

This DPR data call-in to re-evaluate the mostly widely used pyrethroid products comes after California water quality regulators began an exhaustive and onerous program to test all California waterways for anything and everything. Some of these tests found pyrethroids bound to creek bed sediments and therefore toxic to some aquatic organisms. This was the first shoe to drop.

The first pyrethroid sediment studies were published in 2004. DPR announced its intent to issue a pyrethroid re-evaluation in November 2005 and discussions with registrants and the department's technical staff continued in January and February 2006.

DPR will require detailed scientific data on 608 products from 123 registrants with deadlines that range from six months to two years, depending upon the complexity of work. Review and analysis will proceed as the data comes in.

The data call-in serves two purposes, said DPR Director Mary-Ann Warmerdam. “First, we must take all appropriate steps to protect the environment,” she said. “While these products do not pose any immediate threat to people, their impact on aquatic ecology must be assessed so that we can take appropriate actions under state and federal clean water law.

“Second, pyrethroids are a valuable pest management tool, and they are much less toxic than some of their predecessor chemicals,” she said. “It is in everyone's interest to address any problems early and develop preventive strategies as needed. Simply switching to another chemical is not the answer, since it could lead to more water quality problems.”

Members of the state's pesticide industry also are involved. After the first pyrethroid sediment studies were released in 2004, the Coalition for Urban/Rural Stewardship (CURES) began an outreach campaign. In the last two years, CURES has held 30 presentations for more than 2,000 growers, crop advisors and urban pest professionals.

The group also is sending out 10,000 best-management practice guides to orchard and row crop growers. “Pyrethroids are important tools for protecting crops, people and their homes from pests,” said CURES Executive Director Parry Klassen. “Proper stewardship will ensure the products can do this safely without impacting the environment.”

Those practices include preventing drift to waterways, no applications before rainstorms and keeping soil from washing off treated areas by irrigation or rainfall.

Pyrethroids are important tools for protecting crops, people and their homes from pests. Proper stewardship will ensure the products can do this safely without impacting the environment.

“All pyrethroids undergo a battery of tests and safety assessments to satisfy the stringent regulatory requirements of the U.S. Environmental Protection Agency before they ever enter the market,” Klassen said. DPR conducts similar evaluations before pyrethroids can be used in California.

All pyrethroids continue to meet the most modern EPA safety standards as they are continually monitored and re-evaluated by EPA. Based on this, when used according to labeled directions, pyrethroids do not pose unacceptable risk to humans or the environment.

Pyrethroids generally have favorable environmental and toxicological profiles and industry has continued to find ways to ensure the lowest risk and exposure possible. The newer synthetic pyrethroids are effective at much lower rates than the earlier pyrethroids, so less chemicals need be applied to the crops reducing the amount that can potentially move off target, Klassen noted.

Pyrethroids are extremely unlikely to be found in groundwater because they bind extensively to soil and are readily broken down in the soil by micro-organisms, eventually to carbon dioxide.

Pyrethroids will not generally be found in the water column because they redistribute from water to absorb to soil and sediment particles or to the surfaces of aquatic plants much more rapidly than other agricultural chemicals do.

In agricultural, sound management practices can help prevent runoff, such as reducing the amount of soil transported to soil water using straw bales, and channeling field runoff through grass buffers and settling ponds. In urban settings, practices include ensuring no applications are made near drains or prior to irrigation or storms. Sweeping up granules from hard surfaces and applying sprayer rinse water to treated surfaces (and not dumping in drains) are other practices for urban applications.

“We are always concerned about any possible impacts of our products on the environment, especially water. However, at this time no conclusions can be drawn about the presence of pyrethroids in sediment until California's Department of Pesticide Regulation completes its pyrethroid data call-in and analysis,” Klassen said.