The Silence of the Frogs
Robert McKinnell peels back the white kitchen towel taped loosely over a fish tank containing nearly 40 small, dark-green frogs from Crow Wing county. They're swimming and hopping anxiously in about a half-inch of murky water. "The thing is," he says, "you often can't see their deformities until you pick them up." The University of Minnesota scientist seizes frogs one by one, flipping them around with his fingers to expose the particular defects of each one: missing limbs, extra limbs, webbed legs, extra toes. There was one that had only one eye--or so they thought until they opened its mouth and found the other partway down its throat.
"Where's the five-legged frog?" McKinnell asks a worker in a white lab coat as he rummages around in another tank, tossing frogs back, one after another. "What the hell?" He finally comes up with the one he's been searching for. It's normal looking except for a short leg jutting out from its jaw. The frog squirms in McKinnell's hand. When one of its good legs inadvertently swings over the useless one, he looks up a little like a proud parent. "Look," he says, "he's holding hands with himself."
McKinnell has been examining the habits and diseases of frog populations for almost 40 years now. His main interest is cancer; studying particular strains among frogs has led to some discoveries about human cancers. And he was one of the experts called in to take a look at genetic abnormalities in the children of the people who lived near Love Canal in the 1970s. His role in studying Minnesota's abnormal frogs is to search their DNA and internal organs for clues--parasites, mutations, or whatever else might turn up.
He is currently part of a team of five scientists who are busy taking samples, examining pollutants, and conducting experimental matings in hope of finding out why so many frogs around the state are suddenly so badly deformed. The team, which received emergency funding from the Legislature via the state lottery and cigarette taxes, is trying to figure out not only what's happened to the frogs, but also what the situation might portend for human populations.
Frogs are generally considered biogenetic canaries in the coal mine--indicators of ecological trouble to come. They encounter a wide array of environmental factors, spending their lives in a combination of aquatic and land environments and feeding on both plants and bugs; their eggs don't have shells and thus aren't protected from ultraviolet rays or pollutants. And owing to similarities in liver function, they also process certain chemicals the same way humans do. The shorthand explanation is that humans "have many of the same enzyme systems as frogs," according to McKinnell. "When humans encounter the same substances, they will be activated in humans as they are in frogs. If frogs are abnormal because of the conversion, that is a red flag to people who live in the area."
"Funny frogs," as McKinnell calls them, first appeared en masse last fall in Le Sueur county near Henderson, about 50 miles southwest of the Twin Cities. A group of schoolkids from the Minnesota New Country School were on a field trip to study life around a pond on the property of a retired farmer. The site was once farmland, but it was transformed into a wildlife refuge years ago.
Deformities have now surfaced at more than 20 confirmed sites in seven counties all over the state: Crow Wing, Le Sueur, Meeker, Pope, Scott, Sibley, and Stevens. There are many more unconfirmed sites, with new calls coming in every day. McKinnell feels overwhelmed. "Minnesota is the size of Great Britain. Can you expect two or three scientists to study all of Great Britain? No."
Simply put, the team of scientists (two from the University of Minnesota, two from the Minnesota Pollution Control Agency, and one from South Dakota) is trying to find out whether the deformities are caused by a genetic alteration or chemical agent passed on by parents, or by a more immediate environmental contamination of eggs and tadpoles themselves. They have to act fast because abnormal frogs generally don't survive winters. MPCA aquatic biologist Judy Helgen, who heads the team, says there were some frogs with missing eyes and missing legs reported in 1993 after the massive flooding of the Minnesota River basin, but it was late in the year and scientists only found one specimen. When they went back the next year, the site was breeding normal frogs. There wasn't time to pinpoint a cause, says Helgen, but "what we are seeing now is different"--more widespread, and probably longer-lasting. "Here we may have a better chance to set up longer-term research," she says. "I don't think this can be understood in one summer. It may take three to five years to figure out."
To get an idea of possible environmental factors, they're working to determine what all the sites have in common. Looking at a map, the counties in question make sort of a diagonal stripe from the upper-left corner of the state to the lower-right corner, with a few falling in unrelated areas such as the spot near Brainerd, in Crow Wing county. They lie in a variety of drainage bases, militating against toxins from a single river as the cause.
At first, the scientists were convinced that the deformities were related to some stirring up of old soil; all the ponds were either man-made or altered in some significant way. But then some ponds turned up that hadn't been excavated at all. McKinnell points out one theory, in an uncharacteristic fit of speculation, that all are near highways: "The highway department sprays and sprays herbicides along the highways. They apparently don't want to see anything blooming."
Helgen and the MPCA are taking sediment samples to check for heavy metals (mercury, selenium, arsenic, and cadmium) and are checking the water for pesticides, some of which have been found to cause human birth defects. Vincent Garry, another UM researcher, recently found that in regions with heavy use of certain fungicides and herbicides, children are 1.5 to 2 times more likely to have birth defects than those in the rest of the state . He also found that kids are more likely to have problems if they are conceived in the spring when the chemicals are applied to the fields. "We're trying to establish whether there is something in the eggs of the adult female frog," says Helgen, "which means we have to look at the whole landscape they live on. They feed on the landscape, on insects. So whatever those insects might be bio-accumulating might be getting into the frogs that way. Or maybe they are passing through vegetation and picking things up.
"It's kind of up for grabs. I'm curious to see if there is something new being used in the past few years [on crops], something unbeknownst to any farmer that is approved and legitimate, but might have a different chemistry or inert ingredient. That could be the cause. We're just trying to understand, why is it different? Why are we seeing deformities a little in '93 and a lot more in '95 and '96?"
One can't assume that agricultural chemicals are to blame, cautions Helgen. In another of a long line of confounding circumstances, some non-agricultural sites have turned up: wooded areas, lakeside cabins, places with no direct runoff. Recently there was one still-unconfirmed report from a pond in the middle of a Douglas county golf course. Maybe a search of landfills will provide a clue. Helgen can only guess.
David Hoppe, a biologist at the University of Minnesota at Morris, has been working with frogs since 1975. He and McKinnell think the problem lies in the water. "I've never seen anything like this," says Hoppe. "And yes, it does alarm me." Aside from any implications the situation may have for people, he says, "it's alarming with regard to the frogs themselves. The high frequencies are certainly going to impact the frog population. Landowners ask me if people should be worried. Without seeing the chemical data, I can't say."
So far, Hoppe has found three sites where multiple species share deformities, the most telling in Crow Wing county. There he's found deformities in American toads and mink frogs, as well as in leopard frogs. Mink frogs have shown some of the highest rates of defects: an average of 45 percent. Interestingly enough, notes Hoppe, mink frogs spend the most time in water of the three. The rate of defects for leopard frogs ranges from 10 to 60 percent; for American toads, which spend the least amount of time in water, it's only between 1 and 5 percent.
"These [seem] like birth defects that are environmentally caused," says Hoppe. "A lot of evidence points to that. There are such an array of different defects. It's in different species occupying the same pond. It's in some ponds and not other ponds. I'm keeping my mind open. When we get the results of the chemical analyses we will have better ideas. There are just too darn many variables in this experiment. I'd say it's a particularly complicated situation. There are a whole array of chemicals. Then there are synergistic reactions between chemicals that tend not have been studied. Maybe one chemical is all right by itself. As they biodegrade, chemicals can become more nasty than the original chemical. You have airborne chemicals. You have runoff. You have those that are already in the sediment. Heavy metals have caused deformities in the past, but so have pesticides and parasites. So have abnormal temperatures. Overcrowding has caused deformities."
Hoppe sounds at once exasperated and sad at what he's finding in the state's swamps and wetlands. "I've seen mink frogs with as many as four extra legs sticking out. Or they will have like a club foot. There are mild defects and some really gross-looking things. I've seen frogs with no hind legs. I've seen frogs with so many extra, partially formed legs they can hardly move around. I've seen some with hind legs so deformed they drag themselves along. It's getting hard to look at."
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