Residential runoff poses environmental danger

Farmers have gotten a bad rap as big-time polluters because of runoff from chemicals they use on their fields. But proud homeowners may do more damage, says a toxicologist from Southern Illinois University–Carbondale.

“More than 90 percent of the sediments we collected from creeks that drain a subdivision in Roseville, Calif., were toxic to an aquatic organism (equivalent in watery worlds to the ‘canary in the mineshaft’)—that’s pretty remarkable,” said Michael J. Lydy of Southern Illinois University’s Fisheries and Aquaculture Center.

“We’re talking acutely toxic here—these animals are dead. And this toxicity was [caused by] runoff from storm drains in people’s yards.”

What made the runoff so deadly? Pyrethroids, the chemicals that give bug sprays made for both home and farm use their knock-out power.

“You might find two or three of these in agricultural runoff—it’s a pretty simple mixture,” Lydy said. “But in runoff from residential areas, you’ll find seven different pyrethroids and much more complex pesticide mixtures.”

Lydy and colleagues have been tracking pyrethroids in the waterways of central California since 2000.

In earlier work, they found that pyrethroid-rich sediments from rivers, creeks and irrigation canals in a 10-county agricultural area in the Central Valley had killed nearly 70 percent of a shrimp-like bottom dweller called Hyalella azteca.

 “What our study did was to link pyrethroid concentrations in sediments from field samples, the dead animals in our lab and a native field population that is no longer there.” Lydy said.

“We had Hyalella living in a stream prior to the subdivision being built. It was built, and then they were gone. If you go above the subdivision, the Hyalella are fine.”

There is evidence that marketing decisions by manufacturers may account for the heavy chemical load in today’s lawn care products.

“Twenty years ago you bought lawn fertilizer, herbicide and pesticide in three different bags,” Lydy said. “Now the manufacturers are packaging them all together — it’s just a tool to have you buy more of an unneeded product.”

Homeowners often make things worse by exceeding the recommended application rates.

Of the seven pyrethroids the researchers looked at, bifenthrin proved the most problematic.

“It’s not used for agricultural purposes or for mosquito spraying—we’ve really pinpointed it to structural pest control and homeowner use,” Lydy said.

As information on retail insecticide sales is not available, the researchers did their own “shelf survey” of lawn care products at home supply stores in the Roseville area. All contained pyrethroids, and bifenthrin comprised half of those.

Because such products must receive federal approval from the Environmental Protection Agency, homeowners—and the general public—believe they are safe. But if even 1 percent of the bifenthrin a single homeowner put on the lawn on a Saturday afternoon washed down a storm drain, it would take at least half a million gallons of water to render it harmless to Hyalella.

“And that’s just one application by one person,” Lydy pointed out. “Think how many times a year you see people out spreading this stuff on their lawns. And they don’t want to wash their spreader off on the lawn because that would leave a brown spot. So they take it to the driveway and then push all that water toward the gutter.”

The researchers plan to use their data in additional projects, among them a comparison of agricultural and urban pollution.

The researchers also hope to expand their study to include sites all across the country.

“I think our study suggests ramifications that are important for other urban areas—it’s not just a California issue,” Lydy said.

By K.C. Jaehnig, information specialist, Southern Illinois University.