Researchers found frog abnormalities are not as common as was once feared, but certain "hotspots" have higher rates.
Researchers looked at frog deformity rates for a decade, and concluded they are only present in about two percent of the population, a UC Davis new release reported.
"We now know what the baseline is and the [two] percent level is relatively good news, but some regions need a deeper look," Marcel Holyoak, professor of environmental science and policy at the University of California, Davis, and a co-author on the study, said.
Hotspot areas include the "Mississippi River Valley, California and south-central and eastern Alaska." The team believes there must be a local cause for the finding.
Between the years of 2000 and 2009 a research team traveled to 152 U.S. refuges and collected 68,000 frogs and toads along the way.
The team hoped to discover "why and where" these deformities occurred. The team has not yet determined the precise cause of the problem, but they have mapped out its patterns. They hope looking at the patterns will help them determine the cause in the future.
"We see them at an elevated frequency one year or for a few years, and then they recover," Holyoak said.
Some proposed causes for the deformities were "pollution from industry or agriculture, parasites, ultraviolet exposure and naturally occurring heavy metals leaching into water bodies." Holyoak also notices that the causes could vary across the "hotspot" areas.
The most highly observed deformities were "shortened toes or legs, and skin cysts." Out of the thousands of frogs and toads collected, only 12 were observed to have extra limbs.
"The study comes against a background of a general decline in amphibian populations both in the U.S. and worldwide. For example, the California red-legged frog celebrated by Mark Twain's story is now listed as threatened," the news release reported.
