How Did the Poison Get into the Trout?

And other pollution puzzles of the Great Lakes region

  • Vicki Monks
  • Aug 01, 1998
One thousand feet below the surface of Lake Superior, a lead-weighted steel box settles into the lake bottom, cutting downward until it disappears in soft muck. On board a ship above, University of Minnesota chemist Deb Swackhamer signals a remote-controlled trapdoor to slide shut on the buried box. Then, with a squeal of cable, the box pulls free and returns to the ship.

This box of mud holds clues to a mystery that has perplexed scientists for more than a decade. In the 1980s, biologists found the banned pesticide toxaphene in the lake´s trout, sediment and water. "We didn´t expect this," says Swackhamer. "It just jumped out at us from the data." By 1992, the U.S. Environmental Protection Agency (EPA) was finding an average of 5 parts per million of toxaphene in the trout. That´s far more than the level of the next worst contaminant in the region, about 3 parts per million of PCBs in Lake Michigan and Lake Ontario trout. And the toxaphene discovery was in Lake Superior--previously believed to be among the most pristine of all lakes in the Western Hemisphere.

With these findings, researchers are confirming once again that the Great Lakes region is a hot spot for persistent toxic chemicals in the environment. The waters here are ringed with industry and development that have proven to be sources of pollution. Not only that, for reasons having to do with weather and geography, toxics tend to migrate to the Great Lakes region and then remain here, where they can end up in wildlife. That means scientists are on the alert for possible health hazards such as toxics in fish consumed by people.

Now toxaphene is presenting a new mystery: Although it was banned in 1982, recent research on old samples has found that toxaphene´s levels in the Great Lakes have remained about the same for the last 20 years. And that means that new toxaphene is still somehow coming into the region. If it weren´t, say scientists, levels would be decreasing significantly just as they did for toxics such as DDT and PCBs within a decade after they were banned.

With her boxes of mud, Swackhamer joins a group of scientists that for decades have been solving similar puzzles, many of which have been peculiar to the Great Lakes region. Take the case of DDE, a breakdown product of DDT. In the mid-1980s, 15 years after DDT was banned, biologist Dave DeVault became curious about why DDE was showing up in Great Lakes harbors. At the time, he was manager of the EPA´s Great Lakes Fish Contaminant Monitoring Program. He and another researcher who found DDE in New York´s Finger Lakes suspected smuggling or illegal manufacture. Then a chemist noticed that the structure of this particular DDE was unique. After nearly a year, DeVault´s team traced it to imported Italian dicofol, a pesticide used primarily on rose bushes. The EPA quickly moved to restrict the contaminant.

In another case, in the late 1980s scientists used "fingerprinting" to trace sources of lead in Lakes Erie and Ontario. Because each geological source of lead is chemically unique, geochemist A. Russell Flegal of the University of California, Santa Cruz, was able to trace industrial lead in western Lake Ontario to Canada and lead in the southern half of Lake Erie to the United States.

Then there was the riddle of Great Lakes trout. For 30 years, in all the lakes but Superior, lake trout have not reproduced. Last year, toxicologist Richard Peterson of the University of Wisconsin, Madison, concluded from long-term research that the culprits are likely a group of dioxinlike chemicals. That explanation was not obvious: Once the dominant species in the Great Lakes, lake trout were hard hit by overfishing and predation by parasitic sea lampreys in the 1940s. By mid-century, only a few populations of Lake Superior trout remained. Once fishing was limited and sea lampreys were controlled, it seemed restocking would cure the problem. But introduced trout simply haven´t reproduced.

The main reason, Peterson has determined, is the trout´s susceptibility to the dioxinlike chemicals, which come from incinerators, pulp mills and a variety of industrial sources in the Great Lakes region and persist for decades. "We don´t know why this species is so especially sensitive to these chemicals," he says. Dioxin levels are now falling in the Great Lakes due to stricter regulations put in place two decades ago, and scientists hope the trout will reproduce naturally again.

For the toxaphene detectives, the initial data from Lake Superior trout made no sense. Except for paper mills, the polluting industries that line the shores of the other Great Lakes don´t do much business around Lake Superior, which has been less contaminated than its sister lakes by well-known villains like PCBs, dioxin and mercury. So why the toxaphene? "I didn´t know what to make of it," says DeVault, now a U.S. Fish and Wildlife Service biologist. Perhaps other chemicals were interfering with the analysis. Perhaps the trout had switched to food sources laden with toxaphene from the past.

Still, the finding was disturbing. The name toxaphene refers to a group of turpentine-smelling chemicals made from pine oil and chlorine. It was supposed to be the safe alternative to DDT. Toxaphene became one of the most heavily used pesticides ever--as much as 46 million pounds a year during the height of its use in the 1970s, according to the U.S. Agency for Toxic Substances and Disease Registry. In the United States, most of that was sprayed on cotton and soybeans in the South, but it was registered for use in more than 800 products--for everything from tick control on livestock to the killing of unwanted fish species in lakes and ponds.

Before long, toxicologists found that the pesticide was not so safe. According to the agency, high-level or long-term exposure can damage the lungs, nervous system, liver, kidneys, adrenal glands and immune system. It can disrupt endocrine systems and raise cancer risk. The chemical takes years to break down in the environment, and low levels have been linked to birth defects and reproductive problems in animals.

The EPA banned toxaphene because of its potential to cause cancer and birth defects. Scientists aren´t certain what level of toxaphene exposure might cause health problems for humans. The Canadian government advises citizens to avoid eating Lake Superior trout altogether because of toxaphene contamination. U.S. warnings are not so strict, but some health officials are concerned about people who consume a lot of Lake Superior trout. Says DeVault, "The present concentrations in fish are high enough to be causing reproductive problems for the fish themselves. And I think there may also be some real human health issues." Says water-pollution expert Wayne Schmidt of the National Wildlife Federation, "Just when we think we´ve eliminated a very dangerous chemical from our environment--surprise, surprise--there it is in the greatest freshwater lake in the world, at levels in the fish that are of concern for consumption by people."

Among those most concerned are the Chippewa of northern Minnesota and Ojibwa of Ontario, Canada. Trout is a significant portion of their diets, and fishing is central to cultural traditions. "When there are contaminants in subsistence foods, they pose much more than a physical health threat. It has an impact on spiritual, mental and emotional health as well," says Maxine Cole, coordinator of the EAGLE Project, an environmental health-research undertaking. In one of its studies--among the first of its kind in the region--the researchers are checking blood and hair samples from Native people to determine exposure to toxaphene and other contaminants.

But before anything can be done to stop contamination, scientists must determine its source. There´s a long list of suspects. Atmospheric fallout and local sources are both strong contenders. In 1996, an international meeting of academic and government scientists determined that there is evidence for local sources of toxaphene in the Great Lakes. Comments DeVault, "This was very important, because it was the first time that the larger scientific community supported our conclusions." Those sources may be leaks from old, unidentified toxic-waste dumps or industrial sites. There´s also the possibility that some toxaphene lingers from past attempts by U.S. and Canadian agencies to control fish populations and kill sea lampreys with the stuff.

A few laboratory studies suggest toxaphene could inadvertently be formed during paper-making, and that is what goes on in the pulp and paper mills that operate around Lake Superior´s Thunder Bay in the otherwise pristine wilderness surrounding the lake. "The pulp and paper industry was the one place where you have pine oil and chlorine--which go into formulating toxaphene," says DeVault. But, he adds, the evidence is far from complete.

In 1997, the EPA began studies that include sampling of river sediment upstream and downstream from pulp mills. EPA spokesman John Dorkin says the agency expects the results to pinpoint potential sources of contamination. The studies won´t be complete for at least a year. In the meantime, paper-industry scientists argue the pulp mills can´t be the culprits. Toxaphene formation requires ultraviolet light, and pulp bleaching is done completely in the dark, they say. Whether that is true has not been established conclusively. Still, Jerry Schwartz, director of water-quality programs for the American Forest and Paper Association, blames atmospheric deposition. "This mystery, as you call it, is really not so much of a mystery," he says.

According to Swackhamer´s research, Schwartz is probably correct that the atmosphere is at least partially responsible--at least in the case of Lake Superior--through a process called "the grasshopper effect." Much of the toxaphene sprayed on cotton in the South has remained in the soil, and on any sweltering summer day some of it vaporizes, in the same way mothballs and air fresheners release particles into the air. The toxaphene catches the wind, falling back to Earth when it hits cold air. "Each time the toxaphene jumps back into the air--that´s the grasshopper part--it moves farther north," Swackhamer explains. But once it falls into Lake Superior, the grasshopper is pretty well spent. The 31,820-square-mile lake, 1,290 feet deep in places, never gets warm enough to allow much toxaphene to go airborne.

Canadian researcher Terry Bidleman of the Atmospheric Environment Service has documented toxaphene carried by the grasshopper effect as far north as the polar ice cap. Polar bears, seals, fish and other animals store toxaphene in their fat. "A ghost from the past," Bidleman calls it. "Sometimes you wish you could just go up there and give the Arctic Ocean a big old flush and get everything out."

Lake Michigan holds a further mystery. Toxaphene concentrations are highest in the northern end of Lake Michigan, which is far less developed than the southern end, and Swackhamer is convinced that atmospheric deposition is not the reason in this location. "If you have an atmospheric pollutant coming into the lake, it gets pretty well mixed," she says. "So you´d expect sediments in the north to look like sediments in the south."

There are dozens of paper mills around northern Lake Michigan, along with plenty of other possible sources too. "Most of the time we get involved in cases like this it´s not just Ôone of the above,´" says EPA´s Dorkin. "It´s all of the above--a little of this, a little of that. It makes it difficult to fix the problem." Which brings us back to the point of the scientific sleuthing. Atmospheric transport of pollutants that are already released into the environment can´t be controlled. "There´s no way you could remove all the contaminated soil from the southern third of the United States," Swackhamer says. "So it´s really a matter of learning from the mistake by studying it. I´m sure that way back when, they didn´t have any idea that long-range transport was going to occur to the extent it has."

Once upon a time, DDT was promoted as being safe. Later on, promoters made the same claims for toxaphene. "How many generations will it take before the environment finally can purge itself of the mistakes that were made in the past?" asks NWF´s Schmidt. Perhaps the most crucial mystery to explore will be figuring out how our actions today will change the world tomorrow.

Writer Vicki Monks of Santa Fe, New Mexico, is a frequent contributor to National Wildlife.

Protecting the Great Lakes: NWF Takes Action 
NWF is joining forces with the U.S. and Canadian governments, citizens, businesses and tribes in the Great Lakes region to stop toxic releases at their sources. One main goal is to make Lake Superior a zero-discharge zone where the nine worst toxics are eliminated.

Other efforts include replacement of mercury-containing hospital equipment with effective nontoxic substitutes and formation of a campus cooperative for purchasing chlorine-free paper. NWF is also advocating a U.S.-Canadian agreement on tough reductions and timelines for the eventual elimination of air toxics. To learn more, visit web address

Get Involved

Where We Work

More than one-third of U.S. fish and wildlife species are at risk of extinction in the coming decades. We're on the ground in seven regions across the country, collaborating with 52 state and territory affiliates to reverse the crisis and ensure wildlife thrive.

Learn More
Regional Centers and Affiliates