The Silence of the Frogs

A team of scientists labors to figure out why so many frogs around the state are suddenly turning up deformed--and what

           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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