Environmental Biologist Dr. Donald Weston worries about Hyalella azteca, the tiny shrimp-like crustaceans that live -- and increasingly, die -- in Contra Costa County creeks. And speaking at a recent Friends of Orinda Creeks community gathering, Weston was equally concerned about the Chironomus dilutus, a wee red worm-like invertebrate.

Like most things scientific, it was complicated. But it didn't take a PhD to understand why concerned citizens and a group of advanced environmental science students from Campolindo High School in Moraga buckled down and focused on Weston's 30-minute powerpoint presentation. The big worry -- that pesticides leaking into Contra Costa County creeks are killing our spindly little amphipod and winged-insect friends.

"When we apply these chemicals to our lawns, it's not staying on our lawns and gardens. The toxicity is not limited to little creeks," he said.

Research by Weston, a professor emeritus in UC Berkeley's Department of Integrative Biology, primarily addresses how human activities -- especially activities that release toxins -- impact aquatic organisms and sediment.

The Hyalella crustaceans, Weston explained, are hypersensitive to pyrethroids, a class of insecticide used by professional lawn care companies and found in common products like Raid and Scotts Turf Builder with SummerGuard. The bucolic term "SummerGuard" is actually the company's name for pyrethroid, according to Weston.

Chironomus, on the other hand, are killed by exposure to fipronil, a pet medication. Frequently used by pet owners to kill fleas in dogs and cats -- Frontline products are a familiar brand -- professional exterminators also use fipronil to control ants and termites.

"Once it's in the environment, it degrades into many different things," Weston warned -- things far more toxic than the parent pesticide. Although Weston said it's not used as much as pyrethroids, its levels are above what sensitive species can tolerate. Counterintuitively, the only thing scarier than lethal pesticide levels, Weston said, are recent studies showing Hyalella pesticide resistance is building. In Grayson Creek, that flows through much of Pleasant Hill, he said "even huge amounts of pesticide" were not killing the Hyalella.

"It scares us, because that tells us there's enough pyrethroid in the creek to cause them to mutate. The sensitive pests have been killed off; the rest have mutated and survived."

Leaving future research to answer a question about how this might translate into water that is dangerous for human consumption, Weston said compelling evidence that toxic chemicals from our lawns are impacting aquatic life is, in itself, important.

Water tested in Roseville, 15 miles north of Sacramento, gave researchers the first clue that creeks were becoming virtual pesticide leakage lanes, delivering urban lawn chemicals into area waterways. Subsequent findings in Pittsburg's Kirker Creek, Oakland's Glen Echo Creek and other Sacramento/Bay Area creeks revealed varying degrees of toxicity; from nearly non-existent to mortally toxic. A 2004 study including two Orinda creeks (Lauterwasser and San Pablo) and Walnut Creek's Pine Creek showed toxicity levels of 64 percent Hyalella dead (in Orinda) and 100 percent dead in Walnut Creek. Urban runoff data, taken between 2006 and 2010, showed all communities in the Sacramento area and the Bay Area had toxic levels, especially after a rainfall.

The half-life of pyrethroids is approximately 30 days, but once they get into creek sediments, that can stretch to years. With 13,300 pounds of the pesticides used by Contra Costa County professional pest controllers alone -- not including private citizens' use -- Weston said, "We'd have to flood the county 6,046 feet deep to dilute it enough so that Hyalella could live. That's equal to two Mount Diablos, stacked on top of each other."

With an American River study showing high pesticide concentrations due to feeder creeks and tributaries, Weston said the Sacramento River is toxic. Because of his lab's findings, he said regulatory response led the State of California to initiate a re-evaluation of 600 products in 2006. New rules were released, restricting the use of pyrethroids, monitoring sewage treatment plants and putting urban creeks and the American River under the watchful care of the Clean Water Act 303(d). This May, the California Department of Pesticide Regulation introduced action against fipronil, aiming to reduce manufacturers' use without a formal, EPA re-evaluation.

For homeowners and members of the Orinda Creek community group, Weston recommended reconsidering maintenance contracts with professional pest controllers, using pesticide-free products, avoiding multipurpose products with unnecessary pesticides and disposing of old products with banned substances. Avoiding the use of pesticides before a rain, when irrigating a lawn, or near hard surfaces, would significantly lower runoff levels. For additional information, he suggested visiting http://www.ipm.ucdavis.edu/ or www.orindacreeks.org