Frogs and other amphibians have hit hard times in the past decade or two: Their populations are down worldwide. Explanations abound, but now a team of researchers thinks they have new evidence that one culprit, pesticides, might be harming the critters. Unexpectedly high numbers of frogs in some of California's national parks, the researchers report, have pesticides in their bodies.
The pesticides, diazinon and chlorpyrifos, are commonly used for agriculture and in household bug sprays. Neither is used much in the national parks along California's Sierra Nevada mountain range, but prevailing winds blow the chemicals into the mountains from California's Central Valley, which is heavily agricultural.
To find out whether pesticides are taken up by amphibians even in relatively pristine areas, a team led by wildlife biologist Donald Sparling of the U.S. Geological Survey in Laurel, Maryland, tested Pacific treefrogs in several national parks. More than 50% of the frogs in Yosemite National Park and 15% of those in Sequoia National Park and the Lake Tahoe area had diazinon in their tissue, the researchers will report in the February issue of Environmental Toxicology and Chemistry. In contrast, no diazinon was found in frogs on the coast or at Lassen Volcanic National Park, areas that lie upwind of agricultural areas. Chlorpyrifos was more widespread, present in around 18% of Yosemite, Sequoia, and Tahoe frogs, compared with 10% of coastal and Lassen frogs.
Pacific treefrogs remain abundant, but Sparling says the frogs serve as a sentinel species for threatened or endangered amphibians in the Sierras. But not all biologists are comfortable with drawing a connection between the pesticides and dwindling populations: "They're not looking at any declining species," says ecologist Carlos Davidson of California State University, Sacramento. But Davidson says that the new study provides site-by-site pesticide data for the first time and gives "a strong heads up that says we need to look at this issue a whole lot more than we have."