Frogs living in remote mountain ponds in the Sierra Nevada are ingesting pesticides used to grow crops 50 to 100 miles away in California's Central Valley, according to a study by government scientists. Researchers from the U.S. Geological Survey identified 10 distinct chemicals in the frogs' tissues, including residues of DDT, an insecticide that's been banned for more than 40 years.
No Kermit, it's not easy being green.
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 considered excellent indicators of ecosystem health due to their sensitivity to environmental change. And while they're not as charismatic as polar bears,"they are a part of the food web," said study leader Kelly Smalling, a research hydrologist who monitors pesticides in amphibians for the U.S. Geological Survey.
"If frog populations decline, you're going to have an increase in insect populations," Smalling said. By by protecting them, "you're keeping the food web balanced."
And their populations are declining. Badly.
A recent study of frogs in the U.S. showed that even populations of species thought to be doing well are disappearing at a rate of almost 3% per year.
They're so fragile that Congress created the Amphibian Research and Monitoring Initiative in 2000 to keep track of the vulnerable animals.
Study co-author and herpetologist Gary Fellers of USGS began monitoring frogs in California in the early 1990s. In 2009, as Fellers prepared to do his usual counts, Smalling decided to tag along to see whether pesticides were contributing to amphibians' demise.
Before long, she was in Yosemite, wading around ponds at night and imitating mating calls When a male responded, she and Fellers would "scoop them up in a net" and then euthanize them, she said.
The pair collected frogs from seven sites in the Sierra Nevada, ranging from Lassen Volcanic National Park in the north to Giant Sequoia National Monument in the south. All of the animals were members of the species Pseudacris regilla, an impossibly bright green creature about the size of a half-dollar, according to the study.
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.
While the chemicals are not used in the vicinity of the frog ponds, they can travel through the atmosphere.
"They're moved by the prevailing winds," she said. "They're either released via dust or precipitation."
The researchers were surprised that none of the pesticides discovered in the frogs were detected in water samples from the ponds where the frogs lived. Very few of the chemicals were found in sediment samples either.
Many studies examining the effects of chemicals on wildlife place more emphasis on collecting samples from water and soil rather than the animals that live in and on them. But the results of this study highlight the problems with that approach, Fellers said.
"The frogs are being exposed to much higher concentrations than we would have suspected just by doing the basic environmental sampling," he said.
Now that pesticides have been in frogs, the next step is to figure out their effects. Death is not the only outcome that concerns Smalling and her team. "Even if concentrations are not high enough to be lethal," the chemicals could leave the frogs more vulnerable to diseases, they wrote.