deadly mix.
In laboratory studies, some combinations of pesticides were far more lethal exposure to simple compounds.
NOAA / Doug Walker
of salmon in the Pacific Northwest of the United States, and elsewhere, were in a world of pain for decades. One of their main enemies is agricultural chemicals, such as chlorpyrifos. The pesticide interferes with the brains of salmon and impairs their ability to feed, according to studies by the zoologist Nathaniel Scholz of the National Oceanic and Atmospheric Administration in Seattle, Washington. Now research shows that Scholz of pesticide mixtures are even worse for salmon and can be surprisingly lethal.
chlorpyrifos and other organophosphorus pesticides called kill cells by inhibiting acetylcholinesterase, an enzyme that helps neurons communicate. These pesticides are sprayed on crops and are widespread in streams in the Northwest; half of the water sampled by the US Geological Survey contain six or more pesticides. In their previous work with salmon, Scholz and his colleagues had only looked at the effects of a pesticide. To get a more realistic idea of exposure, they designed lab experiments to test the effects of mixtures of chlorpyrifos and four other pesticides, exposing juvenile salmon to two compounds both.
At higher concentrations, which exceeded the natural conditions all the different combinations of pesticides inhibited acetylcholinesterase activity of at least 50% - a level of impact behavior. The two lower levels were more realistic, and at this level, a quarter of combinations put a crimp on acetylcholinesterase. What is particularly important, Scholz said, is that the total impact was greater than the sum of two pesticides, demonstrating a synergistic effect.
The biggest surprise was the strength of the synergistic punch pesticides diazinon and malathion, which killed all exposed salmon. Even at the lowest concentration, the fish were extremely ill, says Scholz. "It opened my eyes," says Scholz. "We are seeing relatively dramatic departures" of what happens with each pesticide by itself.
Scholz says the findings, which are under consideration for publication, means that the US Agency for Environmental Protection may be underestimating the hazard pesticides pose to salmon. With hundreds of millions of dollars spent to help salmon populations recover, it is crucial to have a good handle on the greatest threats, he added.
"It is quite an advance that they were able to examine it in this detail," says toxicologist Derek Muir of Research Aquatic Ecosystem Protection Branch of Environment Canada in Burlington, Ontario. "It's a pretty important job," he said. Because there is a lot of information about where pesticides are sprayed, Muir continues, it may be possible to estimate the impact on wild populations. But factoring in all other chemicals in waterways will be difficult, he warns.
Related Sites
- More information on salmon recovery efforts
- organophosphate toxicity
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