April 2007
Lawn & Garden Pesticides Poison Suburban Streams
Yard and garden insecticides have shown up in suburban streams at levels that can wipe out tiny shrimp-like creatures that live on stream bottoms. The culprits are newly popular pesticide products that contain pyrethroids -- chemicals with "thrin" names like cypermethrin and bifenthrin.
This is an old story with a new twist.
Many pesticides are tested to see if they are toxic to water-dwelling insects and crustaceans that are an integral part of stream and river ecosystems. For example, small aquatic organisms are part of the food chain -- necessary for maintaining healthy populations of many fish.
Just a few years ago, diazinon and chlorpyrifos were popular home and garden insecticides. Urban waterways were contaminated by these two chemicals at levels that regularly exceeded benchmarks for toxic effects on water-dwelling creatures. Tests of streams across the United States showed that, each year, 83% of urban streams reached harmful levels of insecticides compared to 53% of agricultural streams.
After residential uses of diazinon and chlorpyrifos were phased out because of health risks, other pesticides took their place. A California water quality agency wanted to know what chemicals were being used so that they could assess water quality for aquatic wildlife. They gathered data from pesticide use reported by landscape and pest control companies, as well as information about store sales of pesticide products. Pyrethroid-containing products were among the new front-runners for lawns, gardens, and houses.
While diazinon and chlorpyrifos are found in the water itself, the pyrethroids are found in sediment because they easily bind to soil. When researchers tested sediment from creeks in a suburban neighborhood, they found pyrethroids in every single sample!
Although pyrethroids have been around for 20 years, there were no studies about their effect on small water creatures that live in the bottom of streambeds. In their laboratories, researchers exposed the shrimp-like Hyalella azteca to samples of sediment. Almost half of the sediment samples were so toxic that all of the Hyalella died.
Three pyrethroids — bifenthrin, cypermethrin, and cyfluthrin — were especially toxic to Hyalella azteca, which is one "indicator" species for healthy streams. Bifenthrin was detected in one of the suburban streams at levels that were 15 times higher than earlier tests of agricultural streams.
Researchers were able to confirm their findings by looking for wild Hyalella azteca in the same streams. Some small tributaries had stretches that were completely devoid of Hyalella. These sections had the most pesticide-contaminated sediment.
Substituting one pesticide to another can just be a toxic trade-off. Researcher Don Weston said, "Pesticides are often cheap, but most people don't recognize the environmental costs of using them."
Individual choices can make a difference. Weston says that "the answer lies in changing practices and changing the mentality of pesticide application in the urban environment."
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