Common agricultural pesticides that attack the nervous systems of salmon can turn more deadly when they combine with other pesticides, researchers have found. Scientists from the NOAA Fisheries Service and Washington State University were expecting that the harmful effects would add up as they accumulated in the water. They were surprised to find a deadly synergy occurred with some combinations, which made the mix more harmful and at lower levels of exposure than the sum of the parts.
The study looked at five common pesticides: diazinon, malathion, chlorpyrifos, carbaryl and carbofuran, all of which suppress an enzyme necessary for nerves to function properly.
The findings suggest that the current practice of testing pesticides - one at a time to see how much is needed to kill a fish - fails to show the true risks, especially for fish protected by the Endangered Species Act, the authors concluded in the study published Monday in the journal Environmental Health Perspectives.
"We need to design new research that takes into effect the real-world situation where pesticides almost always coincide with other pesticides," co-author Nathaniel Scholz, a research zoologist at the NOAA Fisheries Service Northwest Fisheries Science Center, said from Seattle. Inge Werner, director of the aquatic toxicology laboratory at the University of California at Davis, was not involved in the study. She said while the idea was not new, the findings were definitive, even at levels that don't kill fish outright. "We may not see the big fish kills out there anymore like we used to," she said from Davis, Calif. "But the subtle, sublethal effects that basically render them unfit for survival in the wild are much more important. In certain areas, pesticides really are a very important factor" in salmon survival.
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