A recent press release from the Minnesota Pollution Control Agency (MPCA) says they’re still researching the problem of deformed frogs in Minnesota, and they have a few theories to explain this mutant phenomenon.
The first malformed frogs were discovered in 1993 in Western Minnesota near Granite Falls. Then on August 8, 1995 a group of middle-school students from the New Country School in Le Sueur were studying a nature preserve near Henderson, Minnesota when they found leopard frogs that were missing eyes or legs, or had extra legs. MPCA was notified and immediately began an investigation. In the next couple of years, folks around the world started finding malformed frogs.
Five years later, we still have scientists in the field looking for these mutant frogs, and trying to figure out what’s going on. Currently, an alarming 8 to 12 percent of assessed frogs are exhibiting these disturbing malformations. (Biologists think the “normal” rate of malformed frogs is probably less than one percent.) They find very few such frogs that are older than the current year, because most malformed ones don’t make it through winter. The MPCA press release states, “The problem hasn’t gone away and investigators around the country are hard at it.”
So far, research seems to be revealing that there is no single cause for this mutation. Evidence is building that several factors may be involved, depending on the area where the malformation is occurring. So there’s no smoking gun, no magic bullet. Even the agency’s frog investigators say it’s very hard to determine why Minnesota’s frogs began to get funky in the mid-1990s.
The MPCA press release states that there are currently three leading theories that attempt to explain this unsolved mystery.
Theory #1: Ultraviolet radiation
One theory is that ultraviolet (UV) radiation from the sun plays a role, either through direct toxicity or by breaking down chemicals in the environment into other, unknown compounds. In experiments with UV, the EPA lab in Duluth has produced deformities in lab frogs that resemble some of those seen in the field. And a researcher in Oregon is accumulating evidence that UV deforms Pacific tree frogs there. The MPCA is working with U.S. Geological Survey scientists to measure UV penetration into pond water here, but field observations haven’t yet established much of a link.
Theory #2: Parasites
This theory would provide the easy answer – that it’s a “natural” cause and not really a harbinger of environmental doom after all. In some parts of the country, parasites have caused deformities similar to some of those observed here. But again, parasitologists working with the MPCA investigation have looked for evidence of a parasite link for several years. And, except at one site, they just don’t see it. They see normal frogs loaded with parasites, and abnormal frogs with none. Parasites might be a contributing factor at some sites; but at least in Minnesota, it’s not the tidy explanation some have claimed.
Theory #3: “Something in the water”
Researchers from the National Institute of Environmental Health working with the MPCA’s investigation have shown that frog larvae grown in the lab using water from sites with malformed frogs develop severe abnormalities; water from sites where the frogs are normal produces normal larvae. The malformations increase with the dose, too. The more “abnormal” water you add, the more pronounced the effect. Moreover, filtering the water in these experiments through activated carbon removes the effect, indicating probable organic compounds. Also, adding thyroid hormone to the water moderates some of the effects. Thyroid hormone is essential for normal frog development, so this finding could point to chemicals in the water acting as endocrine disrupters.