Real-world pesticide mixtures harm salmon
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“It’s the norm to find pesticides occurring as mixtures,” says Nathaniel Scholz, ecotoxicology With this year’s salmon run in the program manager at the National Tierney and his colleagues reU.S. Pacific Northwest declared Oceanic and Atmospheric Admincreated river water in the laboraa commercial failure, scientists istration’s Northwest Fisheries Scitory under controlled conditions feel an increasing sense of urgenence Center. These mixtures can with carefully measured levels of cy to sort out the environmental combine in ways that produce the 10 most frequently occurring ills contributing to the decline of effects not caused by the indipesticides in British Columbia’s salmon populations. Pesticides vidual chemicals. In his research, Nicomekl River. The mixture conand metals can be toxic to fish at published in ES&T (2007, 41 [8], tained four major classes of peshigh concentrations and have been 2998–3004), Scholz found that very ticides, including the commonly shown in the laboratory to aflow levels of copper impair fect fish behavior even at very salmon’s olfaction and thereby the fish’s ability to detect low concentrations, but their and avoid predators. Testing effects on real-world populaindividual pesticides offers tions have been unclear. the advantage of ascribing efResearch published in fects to one chemical, he says, ES&T (pp 4996–5001) is the but testing all of the possible first laboratory study to simucombinations in a stream late the low-level pesticide quickly becomes “insurbrew in an actual stream and mountable.” The new study’s to examine its effects on fish. approach is more realistic, The study looked at rainbow but “you don’t know which trout, a member of the salmcomponent drove the effect,” on family, and found that the he says, so further tests are pesticide mix can deaden the Pesticides can cause rainbow trout, members of the required. trout’s sense of smell. This salmon family, to lose their sense of smell. Toxicologists need to test could harm the fish’s ability more-realistic scenarios to to avoid predators, find mates, understand effects of chemicals on and migrate back to sea, the reused agricultural pesticides atrawild populations, notes Barbara searchers say, and could contribute zine and diazinon. The researchers Zielinski, who is at the University to the threatened and endangered exposed the trout to the mixture of Windsor (Canada) and also studstatus of salmon species. Salmon for 4 days instead of the typical 30 ies the fish olfactory system. She also face chronic loss of their freshminutes used in other studies. is now Tierney’s postdoctoral adwater habitats, and this year’s unThe scientists also tested a pesviser but did not participate in the precedented collapse is thought to ticide mixture both at one-fifth new study. The pair are working to be related to unfavorable shifts in and at double the concentrations understand how olfactory damage ocean temperature and food sourcfound in the river. At the lowest affects behavior by studying zees for juvenile salmon. pesticide levels, the fish’s response brafish, an easily reared laboratory The researchers are studyto odor was not impaired measuranimal that is much better undering how pesticides affect salmon’s ably, but they had higher levels of stood biologically than salmon. delicate noses. Most such studenzymes that detoxify contamiIn British Columbia, efforts ies examine the effects of a single nants. In some cases, animals to restore trout populations have chemical, often at high concencan build up these enzymes and yielded mixed results. Hatcherytrations, but real-world streams potentially gain protection from raised fish are being released into contain a mixture of chemicals at later pulses of the contaminant at streams, but Tierney says their very low concentrations, says Keith higher concentrations, which oclong-term survival will likely reTierney of Simon Fraser Univercur commonly in streams during quire that scientists gain a more sity (Canada), the study’s coauthor. runoff events. However, that did complete understanding of the Tierney worked on the study with not occur in this case. Regardvarious causes of decline. “We Jessica Sampson and Chris Kenless of the initial exposure level, have to look at the water quality nedy of Simon Fraser University, the fish did not produce enough of streams before we try to bring Mark Sekela of Environment Canadetoxifying enzymes to prevent salmon into them,” he says. da, and Peter Ross of Fisheries and damage from a later large pulse of —ERIKA ENGELHAUPT Oceans Canada. pesticides. July 1, 2008 / Environmental Science & Technology ■ 4619
