New Life in a Death Trap

Will algae blooming in an acidic, poisonous Montana mine lead us to an answer for Superfund sites?

By Edwin Dobb|Friday, December 01, 2000


Pity the snow geese that settled on lake berkeley as a stopover one stormy night in November 1995. The vast lake, covering almost 700 acres of a former open-pit copper mine in Butte, Montana, holds some 30 billion gallons of highly acidic, metal-laden water— scarcely a suitable refuge for migrating birds stalled by harsh weather. So when the flock rose up and turned southward the following morning, almost 350 carcasses were left behind. Autopsies showed their insides were lined with burns and festering sores from exposure to high concentrations of copper, cadmium, and arsenic.

Today one need only stand on the viewing platform and look at the pit— the lifeless yellow and gray walls that stretch for a mile in one direction and a mile and a half in the other and the dark, eerily placid lake— to see that it's hostile toward living things. Surely nothing could survive these perilous waters. But in 1995, the same year the birds died, a chemist studying lake composition retrieved some rope coated with brilliant green slime and took it to his colleagues at Montana Tech of the University of Montana, an institution locals proudly call the Tech. Having evolved in partnership with one of the world's richest and longest-running mining districts, it remains a world-class engineering and mining school. Grant Mitman, one of just three full-time biologists on the faculty, quickly identified the slime as a robust sample of single-celled algae known as Euglena mutabilis. Life had somehow established an outpost in the liquid barren that is the Berkeley Pit.

For Mitman, finding Euglena proved uncannily fortunate. At Dalhousie University in Halifax, Nova Scotia, where he received his doctorate, his passion was algae. "I trained all my life to be a marine biologist," he says, noting the irony in then having taken a post at an engineering school in the Rocky Mountains. Just as a landlocked, man-made toxic lake has reunited this scientist and his favorite subject, so too has it galvanized the long-standing interest of chemists Don and Andrea Stierle, a husband-and-wife team who also work at the university. The Stierles have spent their lives searching for naturally occurring compounds that can be used in agriculture and medicine. For them, the menagerie of small organisms— more than 40— discovered in Lake Berkeley during the past five years holds much potential.

Even more important, perhaps, is the promise that some of those organisms can be employed to reclaim the lake— and other similar repositories of mine wastewater— by neutralizing acidity and absorbing dissolved metals. Beyond these potential benefits are possible theoretical advances in biology. Each new discovery of a so-called extremophile— an organism adapted to unusually harsh conditions— helps illuminate fundamental biological processes, from metabolic dynamics to the means and course of evolution, both here on Earth and elsewhere in the universe.

Lake Berkeley was born of human appetite and geological happenstance. During the early 1880s, just as electricity was lighting up cities and the need for copper mushroomed, an ambitious prospector named Marcus Daly discovered an enormous deposit of the red metal 300 feet down in his own Anaconda Mine. For the next 50 years, Butte provided a third of the copper used in the United States and a sixth of the world's supply— all from a mining district only four miles square. Thereafter the "Richest Hill on Earth," as journalists often referred to the place, continued to yield vast amounts of metals.

After the Second World War, the shafts grew deeper— one company eventually dug a full mile beneath the surface— but the quality of the ore diminished. Mining officials decided to switch from labor-intensive and dangerous underground operations to open-pit mining, a more efficient method for extracting low-grade ore. Excavation began in 1955, and soon the pit became the world's largest truck-operated mine, along the way displacing some Italian and Serbo-Croatian neighborhoods that had grown up around the original mines on the east end of town. Mining came to a halt in the early 1980s, as did the pumps that had been sucking groundwater out of the mines for a century. The flooding began.

Stroll across the mining landscape of Butte today and you will discover why the water has had such a profound environmental effect. The land is dull ocher, and the air smells like rotting eggs. If you look closely at the waste rock, you will see pyrite crystals— fool's gold— everywhere. These are all signs of sulfur. The bedrock is shot through with it. When exposed to air and water, long-buried sulfide minerals produce sulfuric acid, which also helps dissolve other minerals from surrounding rock. Acid-tolerant bacteria that thrive on iron and sulfur compounds hasten this process, and when the pumps were shut down, the Berkeley Pit became an immense chemical transformer producing ever-greater amounts of toxic soup. Making matters worse, it's self-perpetuating. By all accounts, groundwater will continue to migrate into Lake Berkeley indefinitely. Because of this threat to the community, the Environmental Protection Agency added the pit to the federal Superfund list in 1987. The designation also made it part of the country's largest complex of Superfund sites— a series that includes a good part of Butte and the upper 120 miles of the Clarks Fork River watershed.

Today Lake Berkeley is the country's largest and most unusual body of contaminated water. With a pH of 2.6, it's as acidic as cola or lemon juice. Besides copper, cadmium, and arsenic, the water contains a dozen other metals, including aluminum, iron, manganese, and zinc. But it is precisely because of these harsh conditions that the lake has caught the attention of life scientists. "We divide the organisms we've found into two categories," says Andrea Stierle. Dressed casually in a T-shirt, jeans, and sneakers, the chemist stands in her lab next to a counter covered with petri dishes and Erlenmeyer flasks, each one containing a brightly colored fungus culture. "The first group we call survivors," she explains. "They don't really like the environment, but they put up with it. They're able to defend themselves."

Less numerous but far more interesting to Stierle and her husband are the dynamic lake inhabitants they call thrivers. Like the survivors, these organisms arrive by accident— transported by wind and runoff, deposited by birds, sloughed off boat bottoms or old mine timbers. But unlike their less-prepared counterparts, they actually flourish in the presence of acidity and make use of some of the dissolved metals in the lake. A toxic-waste dump is a biological haven to thrivers. As they reproduce— fungi require only a week to do so, bacteria but a day— characteristics that render them more fit become widespread. Metabolic processes are affected. Or as Andrea Stierle puts it, "New environmental niches mean new microbes, new microbes mean new chemistry, and new chemistry means new chemical compounds."

The stierles have good reason to believe that the microbes in Lake Berkeley are a likely source of useful chemicals. Natural compounds have preoccupied them for 20 years, and their partnership has yielded several notable discoveries. The one that makes them most proud occurred in the early 1990s. Then, research showed that a substance called taxol is an effective agent in the treatment of breast and ovarian cancer. In a third of the women receiving taxol, tumors actually shrank. But the news was bittersweet. Taxol comes from the bark of Pacific yew trees, a species native to the Pacific Northwest but nearly extinct. "Ninety-five percent of them had been cut down or burned as slash," Andrea Stierle says. The few trees left couldn't provide enough taxol to meet demand.

While everyone else concentrated on synthesizing the substance and developing methods for growing yew trees more rapidly, she and Don followed a tactic called "biorational serendipity"— a combination of scientific deduction and clever, if sometimes prolonged, sleuthing. Taxol might be in yew bark, they reasoned, because a parasitic or symbiotic microbe manufactures it there. "Life is everywhere," Andrea says, "and all kinds of bacteria and fungi are found on plants." Often they produce compounds that have never before been seen or exploited. The best-known example, of course, is penicillin, which was first extracted from a mold.

For almost two years, Andrea and Don crisscrossed the Pacific Northwest, taking bark samples and, along with plant pathologist Gary Strobel of Montana State University, testing for the presence of taxol. Finally, in 1992, in bark from a yew tree in Glacier Park, they found what they were looking for— a previously unknown fungus that produces the cancer-killing substance. In honor of Andrea, they named the new organism Taxomyces andreanae and applied for a patent. Five years later, Bristol-Myers Squibb purchased the commercial rights.

The Stierles are using much the same reasoning to study the biota of the Berkeley Pit. "Whether in defense or offense, every microbe uses its chemistry to protect itself," Andrea Stierle explains. In other words, bacteria, fungi, and the like manufacture substances that can be poisonous to other microbes. The generic term for such chemicals is "secondary metabolites"— unique compounds that organisms assemble from the basic building blocks, or primary metabolites, such as carbon or hydrogen, that most living things hold in common. "It's among the secondary metabolites," Stierle says, "that we find natural products that can benefit medicine or agriculture."

After finding a promising secondary metabolite, the Stierles use standard bioassays to tell whether and to what degree it is toxic. The first is called the brine shrimp lethality test. "It's been found that compounds that kill brine shrimp are more likely to destroy cancer cells," Stierle says. A second test involves E. coli, a common intestinal bacterium. If the compound repairs DNA in a damaged E. coli, it might also work against cancer. In another assay, the compound is applied along with z a tumor-causing microbe, to potato slices. Previous research has shown that if the new chemical protects the potato against tumor formation, it could prove useful in medicine as well. So far the Stierles have isolated five novel compounds, all from a single fungus. Each one is lethal to brine shrimp. "We've sent them to the National Cancer Institute for further study," Andrea says.

Because of their success with biorational serendipity, the Stierles fully expect to discover many more new substances among the other fungi and bacteria from Lake Berkeley. "We're taking samples everywhere," Stierle says, "from the surface, the entire 700-foot column of water, the sediments at the bottom." And as time goes by, the odds improve, because with time the thrivers are more likely to undergo change. "Under such hostile conditions the pressure to mutate is intense," Stierle says. "In fact, we may already be seeing the results of natural selection." Clearly the mine flood was an environmental disaster with potentially deadly consequences for snow geese and other creatures, but it is now— 18 years and thousands of microbial generations later— proving an engine of evolution.

While the stierles watch expectantly, confident that contingency will yield a chemical bounty, biologist Grant Mitman is preparing a recipe for directing the community of life in the Berkeley Pit. Some 3 million gallons of groundwater seep into the lake daily, raising the surface by about one foot a month. Engineers predict that in about 20 years the water in the pit will rise to the same level as the surrounding groundwater. From that point on, any more water that enters the ground will flow in the opposite direction. The flow will reverse course, polluting the alluvial aquifer in the valley below the mine and discharging toxic metals into Silver Bow Creek, the headwaters of the Clarks Fork River. To prevent this calamity, the Atlantic Richfield Company, which is responsible for Superfund reclamation costs, have to construct a treatment plant before the critical level is reached. But the process under consideration— treating the water with lime, to which metals naturally bind— would produce between 500 and 1,000 tons of toxic sludge each day. Like many others, Mitman believes there is a better way. His way features his favorite microbes.

"I'm looking for organisms that will clean up the water," Mitman explains. "And I believe algae are the best candidates." Slender, tall, with wire-rim glasses, the 42-year-old biologist manages to appear professorial even as he waxes algal while standing in his walk-in environmental chamber at Montana Tech, holding a flask of light green water in one hand and one of dark green water in the other. The sign on the outside of the room reads "Growth Chamber." It is here that Mitman induces miniature blooms in water taken from the contaminated lake. The emerald bloom is Euglena mutabilis, the first new resident to be identified; its darker counterpart is Chlorella ellipsoida vulgaris, one of four other algae Mitman has isolated. Holding up the flask of Chlorella, he says with unmistakable optimism, "This is what the Berkeley Pit could look like someday."

That green should be the color of salvation might be fitting in a place where so much was sacrificed in the name of industrialization. But behind the symbolism is a compelling biological argument. Certain algae consume metals. Others produce bicarbonate, which reduces acidity. The right organisms in the right numbers, the logic goes, would help remedy the two most noxious features of Lake Berkeley. But that is not the only potential benefit. Algae also convert sunlight, carbon dioxide, and water into sugar. And sugar, Mitman says, "is what makes any system come alive." It's the food that other, larger organisms, such as protozoans and fungi, need to survive. Some of these larger microbes also reduce acidity. But most important, they concentrate metals tenfold whenever they consume metal-eating algae, a process sometimes referred to as biological magnification. And when an organism dies, it drifts into sediments at the bottom of the lake, where any metals it might contain are impounded. "The key," Mitman says, "is to get the algae going first."

That's just what he is doing on a small scale in his laboratory. Under the auspices of Montana Tech's Mine Waste Technology Program, Mitman is systematically concocting brews of Berkeley algae. He varies such factors as light and temperature, but he's most interested in what nutrients each batch receives. Unlike bacteria, protozoans, and fungi, algae feed on fairly inexpensive and widely available inorganic nutrients, such as nitrogen and phosphorus. By doing no more than adding these chemicals, Mitman has been able to trigger an extraordinarily rapid growth of algal colonies. Ironically, Euglena, the organism that launched the current research programs of both the Stierles and Mitman, turns out to be highly resistant to metals. It actively excludes them, flourishing in their presence without making use of them. "We even grew one sample on a piece of solid copper," Mitman explains.

Chlorella has proved more promising. In initial tests, it reduced the mineral content of the pit water by as much as 10 percent. That may not seem like much, but Chlorella is only one of several indigenous organisms that in all likelihood can reduce the lake's toxic contents. And as Mitman says, "Every grain of metal that can be removed will save lots of money in the long run." He is now focusing on another denizen, Chromulina freiburgensis, an alga that has already been shown to concentrate metals in other settings but had never been seen before in acidic mine water. Following the lab work will come field tests. Mitman envisions barrels floating on Lake Berkeley— each housing an experimental brew of ordinary lake water, algae, and various nutrients.

Mitman is convinced that inorganic nutrients can gradually bring about the natural recovery of Lake Berkeley. Creating a big algal bloom could be as simple as spreading nitrate across the surface of the water, or some form of mixing may be the best approach. Some nitrogen-fixing bacteria inhabit the upper levels of the lake, he explains, and when they extract nitrogen from the air for their metabolic needs, they process nitrogen that other organisms in the water can use. In large enough numbers, they could supply the additional nutrients needed to make Lake Berkeley continue blooming on its own.

"Eventually the system could be self-sustaining," Mitman says. Self-sustaining and ever paradoxical. Whether brownish red due to high iron-sulfide content or black because of metal-concentrating algae, Lake Berkeley will remain a fascinating, if forbidding, sight— a testament to nature's resiliency as well as a sobering reminder of the extremes we will go to get the resources we want.

Life, as Andrea Stierle says, may be everywhere. But it is not everywhere guaranteed.







Montana Tech maintains a Web site about the Berkeley Pit's environmental issues: mbmgsun.mtech.edu/env-berkeley.htm.


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