Even in remote Sierra Nevada ponds, the Los Angeles Times reports, frogs are not safe from the deleterious effects of pesticide exposure. Ten poisons applied to crops up to 100 miles away are turning up in the frogs. One of these is “a degraded form of DDT,” the infamous pesticide of Rachel Carson’s Silent Spring, which has been banned in the U.S. since the 1970s.
While the new study, published Thursday in Environmental Toxicology and Chemistry, found only trace amounts of the agricultural chemicals, researchers say that’s almost beside the point: The mere fact that the pesticides had made their way to distant sites in national parks and other public lands was their primary concern.
Amphibians are particularly sensitive to chemicals in the environment since they have one webbed foot in the terrestrial world, another in the aquatic world. And many amphibious species go through a metamorphosis during their lifetimes, which makes them extra sensitive to developmental disruptions.
In this study, U.S. Geological Survey scientists sampled tree frogs in seven sites in the Sierra Nevada, including in national parks.
Back in the lab, the researchers ground up the frogs and screened their tissues for evidence of 98 pesticides. They found 10, including a degraded form of DDT, which was outlawed in 1972. Several of the compounds had never before been observed in frogs.
The three most common chemicals were pyraclostrobin, tebuconazole and simazine, all of which are used to kill pest fungi and plants.
The amount of pesticides found was considered “trace,” but Smalling said it’s impossible to know whether it was enough to cause damage, since these chemicals have never been found in frogs before. “Every pesticide is going to affect organisms differently,” she said.
The chemicals, the researchers say, travel atmospherically to the otherwise pristine sites, where they are deposited on dust particles or by rain and wind up incorporated into the frogs. Oddly, none of the chemicals turned up in water samples where the frogs lived, the L.A. Times reports, and only very low amounts registered in soil samples. The next step is to figure out how, if at all, the frogs are affected by their chemical loads.
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