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Synergistic Toxicity of Pesticides Hurts Salmon

By Dan Flynn and Suzanna Schreck

Pesticides--all the insecticides, weed killers and fertilizers spread on yards and farms--aren't the only problem contributing to the decline of the wild Pacific salmon.
It's the people who carelessly (or unknowingly) overuse these chemicals, says Prof. John Stark, an ecotoxicologist at Washington State University who specializes in risk assessment of threatened and endangered species.
Stark, director of WSU's Puyallup Research and Extension Center, was in Seattle, WA Thursday to deliver a lecture titled "Pesticides, Pollution, and Policy: New Strategies for Saving Pacific Northwest Salmon."  
Stark and other WSU researchers, in collaboration with scientists from the National Oceanic and Atmospheric Administration, are examining the effects of pesticides on salmon biology and behavior, as well as on the organisms salmon feed on.
They're trying to learn why there's been a 95 percent drop in some wild Pacific salmon species since the 1940s, and what role pesticides may play in that decline.
In his lecture, Stark, who has researched salmon for eight years and pesticides for 20 years, focused on improper pesticide use in suburban neighborhoods.
Too many homeowners, he said, overuse pesticides for lawn and garden care.  The chemicals then get flushed into storm drains and the contaminated runoff flows into streams or Puget Sound, Stark said.
"They'll (homeowners) go out and double or quadruple the amount (of pesticides they're supposed to use)," Stark said. "It will say on the label 'apply once or twice a year' and they'll apply it six times a year."
Warning labels on pesticide containers actually carry the force of law, so theoretically someone could get in trouble for misuse, but there's no enforcement and few people even bother to read the product instructions, Stark said.
Stark said the WSU-NOAA research has so far found that pesticides not only can kill  salmon directly, but also may cause neurological damage that affects their sense of smell, hampering their ability to escape predators or find their way back to spawning grounds
And sometimes pesticides are even more detrimental to the aquatic invertebrates salmon feed on, Stark noted. 
One unexpected discovery in the research has been the synergistic toxicity of pesticides, the "chemical soup" that results when multiple pesticides blend together and contaminate salmon habitat. 
When synergism occurs, pesticides grow exponentially more potent and lethal, Stark said.
"It's not one plus one equals two; it's one plus one equals one hundred," he said. 
Because pesticide pollution is so minute--measured in parts per billion, or one part pesticide per one billion parts of water--researchers originally questioned the importance of its impact. But the combined effect of pesticides has shaken their complacency, Stark said.
"Everyone was very surprised," he said. "We did not expect synergism to happen."
Stark doesn't think pesticides should be prohibited, but does support better public education on how to use yard and farm products properly and judiciously.  "Pesticides are a big business and employ a lot of people," Stark said. "We aren't saying ban everything; we're saying let's do this right."
He acknowledged that he has experienced some industry pushback given the controversial nature of the research, especially from those who see the issue as one of fish versus farms.
But it's all matter of weighing risks, costs and values, he explained.  For instance, it's known that copper dust, which flakes from automobile brakes and washes off roadways into local waters, is quite toxic to salmon and is contributing to their decline, Stark said.
Switching to ceramic brakes would solve the problem, but there has been resistance to such a requirement because of the extra cost. 
Salmon tissues does not absorb pesticides, so salmon affected by pesticides are nevertheless safe to eat, Stark said.
Perhaps to emphasize this point, salmon was served at the lecture lunch.
"I had something to do with that--it's kind of a joke," Stark said.

Full post as published by Food Safety News on October 16, 2010 (boomark / email).