Joseph Kiesecker, Ph.D.
Background: Ten years ago, reports of field observations of frogs with severe, non-trauma related limb deformities started to appear in the scientific literature. The first observations were made in Minnesota; however, biologists soon noticed similar abnormalities in other parts of the U.S. The exact cause of the missing and malformed limbs remains to be identified. Also unanswered is the question of whether these observations are a sentinel of human environmental health effects. Possible explanations of the effects include increased UV radiation exposure, parasitic infection, and exposure to environmental chemicals. In new research supported by NIEHS, exposure to environmental chemicals was further investigated.
Advance: In a cross-sectional survey of 42 wetlands in Vermont, limb malformations varied from none to slightly over ten percent. A subsample of the frogs in these regions did not associated parasitic infection with malformation. However, proximity to agricultural land use was associated with an increased risk (odds ratio = 2.26) of limb malformation.
Implications: Although the human health relevance of these findings remains to be determined, they are disturbing none-the-less. Future studies need to focus on determining the exact chemical or mixture of exposures that produce these effects and whether similar exposures in humans would produce adverse effects. Another key need is identifying human health effects that are analogous to frog limb deformities by establishing gene sequence homology between frogs and humans.
Citation: Taylor B, Skelly D, Demarchis LK, Slade MD, Galusha D, Rabinowitz PM. Proximity to pollution sources and risk of amphibian limb malformation. Environ Health Perspect. 2005 Nov;113(11):1497-501.