Low pesticide concentrations, generally below levels that violate state or federal water quality standards, have been detected in five Washington watersheds where salmon are found, according to a new study.
The three-year study by the state departments of Ecology and Agriculture, which was conducted from 2006-08, concluded that the pesticide concentrations are not likely to directly affect salmon. However, levels found at some sites may harm aquatic life that serves as a food source for salmon, some species of which are threatened or endangered.
The lower Yakima Valley had the highest number of pesticide detections that exceeded water quality standards, though the area showed improvement from the last study released in 2006. The area is heavily agricultural, home to thousands of acres of tree fruit, wine grapes, hops and other crops.
In the Wenatchee basin, which was analyzed for the first time in 2007-08, levels of the insecticide endosulfan exceeded standards for fish from mid-March through May. Endosulfan is an insecticide used in the tree fruit industry.
"In the Wenatchee, Entiat area, those levels are a concern and we're working with growers there to see what we can do to reduce them," said Jim Cowles, environmental toxicologist for the Washington state Department of Agriculture.
The study analyzed 1,194 samples for more than 160 pesticides and other chemicals. The analysis detected 74 pesticides or chemicals, with nearly all at low concentrations.
The improvement from previous studies shows growers are doing an even better job, said Heather Hansen, executive director of Washington Friends of Farms and Forests.
She also called it "good news" that pesticide concentrations are not directly affecting salmon," adding the hope that federal agencies would take the data into account as they implement rules to protect endangered species."
"If the federal agencies do not use this current data, our growers will likely face additional, very costly, restrictions," she said.
Erika Schreder, a scientist for Washington Toxics Coalition, said she found it disturbing the degree to which studies continue to find pesticides in surface water.
"There are a number of pesticides that exceed the water quality criteria, and their assessment is that this could harm prey for fish," she said. "I am concerned when I see levels of pesticides that could be reducing the ability for salmon to survive."
Six insecticides, as well as DDT, were periodically found at levels that do not meet water quality standards. DDT has not been registered for use in the U.S. since 1972 but persists in the environment.
The Seattle area's Thornton Creek, the urban area analyzed in the study, showed a significant decrease in herbicide detections over the last six years. In northern Washington's Skagit Delta, pesticide concentrations largely did not exceed water quality standards, but high water temperature and low dissolved oxygen levels were of concern for some fisheries.