MANGANIKA LAKE, MINN. -- Len Anderson grew up eating the fish he caught in the St. Louis River, and he raised his kids to do the same. Now he's teaching his grandchildren to portage canoes in the cold dark of an early morning and wrestle big lunkers of their own.

"It's part of our birthright," said Anderson, who lives in Fond du Lac.

But for the most part, his grandkids can't eat those big fish. They're contaminated with mercury, a toxic air pollutant that falls from the sky, then builds in ever higher concentrations as it moves up the food chain, from microbes to insects to fish -- to people. A recent federal study found that one in 10 infants born on Minnesota's North Shore has potentially unhealthy levels of mercury in their blood, significantly more than those born elsewhere around Lake Superior.

This summer a team of Minnesota scientists, with some funding from the state's taconite industry, have quietly launched a $900,000 research project in an effort to solve an environmental mystery that has puzzled them for years: Why are mercury levels in Minnesota fish among the highest in the Great Lakes region? Why in some cases are they rising? And what, if anything, does 150 years of iron mining have to do with it?

That last question is taking on new urgency as Minnesota gears up for a boom in an altogether different kind of mining -- copper. One of the largest untouched caches of copper in the world lies in northeast Minnesota, and many fear that digging it up will boost water pollution -- including mercury -- as much as it boosts the economy.

As it happens, the sparkling lakes and verdant wetlands that make the Arrowhead region beautiful are also the kind of landscape that is uniquely sensitive to mercury pollution.

Those wet, mucky places are where sulfate, a dissolved mineral that flows from mine pits and waste rock, may play a critical part in the natural alchemy that transports mercury into the chain of life.

"For decades and decades, at an unconscious policy level, we thought that sulfate was pretty benign," said Ed Swain, a leading mercury researcher at the Minnesota Pollution Control Agency. "It was viewed as a tolerable tradeoff. But we didn't have all the information laid out in front of us."

A mercury hot spot

Except for the constant grind of machinery from the United Taconite mine on the other side of a rise, Manganika Lake near Virginia seems like a place untouched by humans. An eagle scouts fish from an island in the middle of the tiny lake, and loons call from the far end. A pod of swans warily keep their distance from Dan Engstrom's overloaded canoe as he pulls up a clear plastic cylinder filled with muck from the bottom of the lake.

"Oh, wow, awesome," Jill Coleman Wasik, a graduate student who is helping Engstrom, said as she examined the perfect core sample of layered mud. "It's a beautiful strata."

Manganika Lake, which is largely unknown and hidden from public view, is a mercury hot spot. At times mercury levels here are among the highest of six sites on the Iron Range tested by Mike Berndt, the scientist who is running the mercury study for the Minnesota Department of Natural Resources.

Now Engstrom, a research scientist with the St. Croix Watershed Research Station, is trying to figure out exactly what dark chemistry is taking place in the muck to affect those mercury levels, and for that he needs a dozen or more tubes of it. Similar analyses are underway at three other lakes and wetlands around the Iron Range, plus deeper looks at how mercury flows through the St. Louis River watershed and into the food chain.

Years of research have revealed some of the process. Today, 90 percent of the mercury that falls from the sky onto Minnesota comes from coal-fired power plants around the world. Bacteria living in the mud at the bottom of lakes and wetlands, where there is no oxygen, gobble up sulfate and, somehow, produce methylmercury -- the most toxic kind and the only kind that accumulates in wildlife.

The mercury they produce is taken up by plankton, and as it moves up the food chain, even small amounts can accumulate into harmful concentrations in fish -- and the animals that eat them.

Loons poisoned with mercury, a neurotoxin, are far less able to produce young, and then do a poor job of parenting the chicks that are born. Scientists have found that up to a fourth of the bald eagles in some parts of the Great Lakes have enough mercury in them to cause neurological damage.

In humans, the risk is greatest for infants and children because mercury affects brain and nerve development. As a result, Minnesota health officials have advised pregnant women and children not to eat certain kinds of fish, primarily large predator fish such as walleye and smallmouth bass, because mercury concentrations are often above safe levels. And recently they've been rising.

Open questions

Sulfate occurs naturally in the environment. It's created when sulfide-bearing rock is exposed to air and water, and 150 years of iron mining in northern Minnesota has exposed a lot of rock. Berndt estimates that massive waste rock piles and canyon-like pits on the Iron Range add 25 to 30 tons of sulfate a day to the lakes and rivers that flow into the St. Louis River, and even more after heavy rainstorms.

Through experiments in a northern Minnesota bog, Engstrom and Wasik have already demonstrated that adding sulfate increases the amount of mercury produced and that reducing sulfate decreases the toxin.

But is that also true in the vastly more complex real world of wetlands, lakes and streams already saturated with sulfate? Or is something else in the cloudy water of Manganika Lake -- the iron, perhaps, or the carbon -- influencing the chemistry?

Craig Pagel, executive director of the Iron Mining Association of Minnesota, said the industry is providing $500,000 of the research budget in order to find some of those answers.

"It would be easy to blame the sulfate," he said. "But they might find there is no connection. What we want is to get good science behind it."

The Great Lakes Basin

At the same time, northern Minnesota is just a small piece of a much larger puzzle involving mercury and wildlife.

Mercury emissions in the United States have declined by almost 60 percent since 1990, although growing economies in China and Africa have pushed the global level 16 percent higher, scientists estimate.

In many places, the amount of mercury found in fish has declined. But the northern Great Lakes are a conundrum: After dropping for years, the amount of mercury in some fish there started rising again in the 1990s. That includes lake trout from Lake Superior and walleye and largemouth bass from Minnesota and Canada.

More than likely, that means that somehow "mercury is becoming more available" to the food chain, said Bruce Monson, a researcher with the Minnesota Pollution Control Agency who tracks mercury in fish.

It could be that invasive species in Lake Superior are playing a new role in the food chain, triggering some new effect on native fish in those deep waters. Or perhaps climate change is generating huge rains like the one that flooded Duluth last week. Those surges of water flush out the wetlands and recycle sulfate and mercury that had been sequestered deep in the muck.

"This is not simple science," Pagel said. "There are no simple answers."

And for northern Minnesota, Engstrom said, it could be too late.

"I leave open the possibility that the damage is done," he said. "These rivers have been contaminated for as long as we've been mining."

Nonetheless, the state's mercury research project could influence major decisions affecting the state's mining industries and its natural environment. Minnesota regulators are reviewing the state's legal standard for sulfate emissions -- now at 10 parts per million -- because of the role it could play in generating mercury and because of its possible impact on another Minnesota birthright -- wild rice.

The answers that lie in those tubes of muck now stored in a laboratory refrigerator could also provide solutions -- what scientists think of as a knob they could use to turn the biochemical process off.

It could tell them that mercury methylization is a problem in only a few places, not the entire watershed. Or it could mean that protecting wild rice and making walleye safe for kids will mean imposing heavy regulations on the state's nascent copper-mining projects and the taconite industry.

In short, Pagel said, the state will face hard choices over the future of mining.

"Do we want it all to go to China?" he said. "We have to balance the economic and the environmental benefits."

Josephine Marcotty • 612-673-7394