In the summer of 1995, a school teacher in northern Minnesota took her class on a field trip in the town of Henderson. A 13-year-old boy started chasing and catching frogs, some of which did not look right. Soon several frogs had been caught with extra legs, missing legs, and other deformaties. According to a Washington Post story on the frogs which ran in early October, 1996, the students began asking their teacher about cancer rates in the area. The teacher alerted a local wildlife biologist, and soon the Minnesota Pollution Control Agency was involved. Over the next two months deformed frogs were found in more than 100 sites in 54 of Minnesota's 87 counties, as well as in Wisconsin and Quebec.
The students who found the first frogs have developed a striking web page, including photos (not for the faint-hearted) of some of the frogs.
Scientists expect that some environmental contaminant is causing the problem. While there are many theories regarding what could be causing the problem, one possible -- and troubling -- explanation is exposure to sulfonylurea herbicides. This class of herbicide has come into widespread use in the Upper Midwest in the last 5 to 8 years; the products are known to be volatile and are extremely active biologically (a tenth of an ounce or less controls weeds on an acre of soybeans) and they are also persistent. Moreover, this class of herbicides are known to adversely affect thyroid function and fetal development, which is why similar human drugs used for treating diabetes are not prescribed to women of child bearing age. It is known that frogs are extraordinarily sensitive to anything that disrupts thyroid function, and that the outcome is deformities of the kind observed.
Some wonder how these chemicals could be reaching some of the isolated lakes where the deformed frogs have been found. The sulfonylureas are applied extensively in southern and central Minnesota farming areas, and along rights-of-way, and may be volatilizing and returning to earth in rainfall in areas many miles away. Many scientists are now actively studying the problem and hopefully the cause will soon be determined. If pesticides are playing a role, there will be another reason to reassess weed management systems.
A January, 1997 article in the Washington Post, "New Reports of Deformed Frogs Trigger U.S. Ecological Alarms" sheds further light on what might be causing the problem. It also notes that similar deformities were found in 1996 in frogs in Lake Champlain, Vermont.