“Virtually every drop of runoff from urban communities was toxic to Hyalella because of pyrethroids,” Weston said.
For the first time ever, Weston and his team documented pyrethroids in the outflow of sewage treatment plants, which was surprising.
“About half of the waste water treatment plants we sampled were toxic,” Weston said. “Most people wouldn’t have expected pyrethroids to get through the system. People figured they would be captured by the slush at the bottom - and probably many of them are - but there is enough getting through the system to make the runoff toxic.”
Agricultural drains, on the other hand, were only an occasional source of pyrethroids, according to the study, published this month in Environmental Science and Technology.
“When you say ‘pesticides,’ I think the average person on the street tends to think of agriculture,” Weston said. “They don’t tend to think of the suburban homes, whereas it turns out the suburban home was a constant source of pyrethroid toxicity.”
The study demonstrated toxicity in two urban creeks and in a 30-kilometer stretch of the American River, considered one of the cleanest rivers in the Delta region.
“The water is totally clear - as clear as the water that comes out of your bathroom faucet,” said Weston. “But the last 30 or 40 miles of the river, once you start getting into Sacramento, are very heavily urbanized. All these communities are dumping their storm water into the American River and it’s enough to cause toxicity.”
Weston said that finding the chemical in the water itself - not just in the sediments - is cause for concern.
“Pyrethroids are very sticky and they don’t like to be dissolved in the water, so most of them are in the sediments,” Weston said. “But it takes so little in the water to be toxic - only two parts per trillion. The state of California now knows not only do they have to worry about the sediment particles, they have to worry about the water as well. And the water travels much farther downstream.”
The levels of toxicity Weston recorded were more than enough to kill a whole host of insects and other invertebrates necessary for healthy river ecology. The researchers have not documented that creatures in the streams have died. But if the water and sediment samples are toxic to the crustacean in the lab, it is a sign they will be toxic to similar creatures in the waterways.
“Bottom dwelling invertebrates and things like stoneflies and mayflies are basically the bottom of the food chain. The concern is whether these insecticides are cutting out this lower rung that the fish depend upon,” Weston said. “This would have not only ecological consequences, but recreational and commercial consequences.”
In response to toxicity concerns raised by Weston's work, California's Department of Pesticide Regulation began reevaluating regulation of pyrethroids in 2006. The state has requested additional data from manufacturers on the safety of pyrethroids and is analyzing at least 700 products used in households and on farms.
When mounting the review, Mary-Ann Warmerdam, director of the state’s pesticide agency, told the Los Angeles Times that the state’s evaluation “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.”
California, Weston said, doesn’t want to return to using organophosphates such as chlorpyrifos, which was banned from household use because of human health concerns, “but they want to control the use of pyrethroids to minimize the environmental effects we document.”