By Peter Montague
The Washington Post reports that frogs with severe birth defects have been discovered during the past two summers in 54 of Minnesota's 87 counties, across Wisconsin and up into the St Lawrence River Valley in Quebec.
According to the September 30 Post, herpetologists have reported finding frogs with missing legs, extra legs, misshapen legs, paralysed legs that stuck out from the body at odd places, legs that were webbed together with extra skin, legs that were fused to the body and legs that split into two half-way down. They have also found frogs with missing eyes. One one-eyed frog had a second eye growing inside its throat.
Robert McKinnell, a geneticist and cancer researcher at University of Minnesota, said he initially thought the reports of deformed frogs didn't amount to much. Frogs have a small number of birth defects naturally. Then McKinnell began visiting various sites in Minnesota and finding a large proportion of deformed frogs (96% at one site). Now he says, "The whole state appears to be affected. We should be alarmed."
Frogs are amphibians. They spend their lives both in the water and on dry land. Beginning life as eggs floating on the surface of still waters, they develop into swimming tadpoles, eventually changing completely, becoming frogs. These major changes in form occur under the control of hormones, which are chemical messengers that travel throughout the organism, turning on and off bodily processes.
Since August 1995, when the first deformed frogs were found in south-central Minnesota, researchers have been searching for the cause, without success. So far, they say, they believe inherited genetic mutations are not involved. This would mean the deformities are being caused by something that affects the frogs during early life, when they are eggs or tadpoles. Judy Helgen, the research scientist who is leading the investigation on behalf of the Minnesota Pollution Control Agency, says she thinks the cause will eventually be discovered to be chemicals of some kind, though it could take several years to pin it down. [Editor's note: The San Francisco Examiner in mid-October reported a study of deformities in frogs in California. The scientist involved concluded that the most likely cause of the deformities was the presence of a parasitic fluke whose numbers might have been greatly increased by fertilisers accumulating in waterways, which increased the quantities of aquatic plants on which it feeds.]
Little research has been done to study the effects of environmental chemicals on amphibians. Most researchers have been focused on confirming or refuting the reported worldwide decline in populations of frogs, toads and salamanders.
Indeed, some of the recently reported declines are large, mysterious and compelling. For example, a study published in April compared amphibian populations in 1915 and 1992 in Yosemite Park in California. The study found that seven kinds of amphibians are declining in numbers, and three have disappeared entirely from Yosemite. Yosemite isn't truly pristine because of air pollution from distant cities, but it is about as clean an environment as you can find in the lower 48 US states. Dr Ronald Heyer, a researcher with the Smithsonian Institution (and chair of the Declining Amphibian Populations Task Force of the World Conservation Union's Species Survival Commission) says, "It's kind of chilling in its effect. Here we have what we consider to be a relatively protected place, and amphibian declines are occurring even there."
Amphibians are particularly sensitive to chemical pollution because they live both in water and on land. Furthermore, they breathe through their skin. Some researchers suspect that toxic heavy metals and pesticides building up in aquatic food chains, plus serious air pollution, may be what's killing some frogs, toads and salamanders.
Many researchers now believe that increased ultraviolet radiation may be affecting frogs' eggs, which float on the surface of the water, absorbing sunlight.
Despite scientists' intense focus on population decline and extinction, recent studies have begun to try to find the causes of birth defects in frogs in Minnesota and Wisconsin.
At the Great Lakes Declining Amphibians Conference in Milwaukee on March 30, Robin E. Jung from the University of Wisconsin at Madison described new studies indicating that leopard frogs collected at a PCB-contaminated site on the Fox River in Wisconsin had more spinal deformities than frogs collected at a cleaner Green Bay site.
A few previous studies had linked frog deformities to pesticides. Still, to date, remarkably little testing has been done to see if environmental chemicals cause birth defects in frogs.
On the other hand, a recent large study has linked birth defects in humans to pesticide use in Minnesota. Researchers from the University of Minnesota and the US Environmental Protection Agency (EPA) linked the Minnesota birth registry for the years 1989-1992 with information about pesticide use across the state. Two pictures emerged: (1) the birth defect rate for all birth defects was significantly increased in children born to private pesticide appliers, compared to the general population; and (2) the general population of western Minnesota (the area of highest use of pesticides) showed a significant increase in birth defects, compared to the rest of the state. This second effect was most pronounced among children conceived during the spring.
In regions where chlorophenoxy herbicides are in use (such as 2,4-D and MCPA), infants conceived in the spring had about 30% more birth defects than infants conceived in other seasons. This effect was not noted in regions reporting low or no use of chlorophenoxy herbicides.
The researchers reported that in the five counties with the highest reported use of 2,4-D herbicide, registered appliers gave birth to only half as many children in 1990 as did the general population. The researchers noted that this finding was consistent with an earlier study showing that 2,4-D is toxic to sperm in pesticide appliers.
The first deformed frogs were discovered in Minnesota in August 1995 by 10-year-olds on a field trip to a farm. After they noticed a one-legged frog, they started collecting others. In a morning they collected 22 frogs, 11 of them with major defects.
"I think the kids got kind of scared", says their teacher, Cindy Reinitz. "They immediately started asking me what the cancer rate was in the area." Now that's an impressive question from a group of 10-year-olds. When all our health officials and corporate CEOs are as alert, insightful and concerned as those children, we'll no longer have to rely on frogs to give us warning.
[From Rachel's Environment & Health Weekly.]