Water link to frog deformities strengthened

In 1995, middle school students on a visit to a Minnesota wetland were startled to find frogs missing limbs or sprouting three and four hind legs. Significant numbers of deformed frogs soon turned up at other sites in the Midwest, as well as in the northeastern, southern, and western United States and in Canada. 

 Since then, numerous explanations for the deformities have sprouted, including parasites, pesticides, and ultraviolet radiation from ozone loss. Federal and Minnesota state researchers last week announced results from continuing studies that point back to the students' initial suspicion: Something in the water can induce deformities.

"We believe that we have shown there is something operating or active in the water," says Mark Gernes of the Minnesota Pollution Control Agency in St. Paul. The next step is "to try in essence to pull that water apart."

 Results of chemical analyses of the water samples are expected within 2 months. Researchers are looking for specific pesticides, metals, and chlorinated contaminants, while also considering all the chemicals present.

 Public interest and health concerns prompted the announcement of the early results, which have not yet been published or released in full. In what officials called a precautionary measure, the agency began providing bottled water to Minnesota residents who live near the sites.

 Water from several wetland sites had a pronounced effect in laboratory tests, says Gernes. Water samples were sent to toxicologists at the National Institute of Environmental Health Sciences (NIEHS) in Research Triangle Park, N.C., who oversaw laboratory tests using African clawed frog (Xenopus) embryos. Researchers grew the embryos in different concentrations of the water samples for 96 hours, then recorded the numbers that died or developed abnormally.

 Undiluted pond water from two of the Minnesota sites caused abnormalities in 100 percent of the embryos, James Burkhart of NIEHS told Science News. Pond sediments, groundwater, and tap water from nearby private wells also affected the embryos' development.

 Water from one site without deformed frogs did not harm the embryos. When water from another of the wetlands considered to be unaffected resulted in some abnormal embryos, researchers returned to the site and found deformities in about 7 percent of the frogs collected there.

"There's complete concordance with an increased incidence of abnormal frogs and the [frog embryo] assays," says Burkhart. 

 It's common to find a small number of malformed frogs at any site -- about 1 percent -- the researchers say. The worrisome wetland sites have had much larger numbers, 10 percent or more. Such sites have been reported in 54 of Minnesota's 87 counties. In some hot spots, among species such as the mink frog, which spends 2 years developing in water, 75 percent of the frogs are deformed, says Gernes. 

 The widespread emergence of high numbers of deformed frogs is probably contributing to the general decline of some frog populations, says David M. Gardiner of the University of California, Irvine. He held a workshop last week to brief developmental biologists about the phenomenon. 

 Because frogs live both in water and on land, they are generally considered to be accurate indicators of environmental health. The embryos' direct exposure to water during development makes them particularly vulnerable to defect-causing agents, says Gardiner. Although human embryos are protected from many environmental influences as they develop, the hormonal pathways controlling limb development in frogs and people can be affected by the same agents, he says.

"If it does it to frogs, it'll do it to people. There's no question about that."

 Although water is now the main focus of research, there are still many questions about other environmental influences on frogs in the wild. "To say that any one thing is the cause of all we've seen isn't viable," says Burkhart.