Mercury: a toxic legacy

Graduate students Douglas Steding (left) and Christopher Conaway collect water samples from the Guadalupe River, which carries mercury pollution from the New Almaden mine into the southern end of San Francisco Bay. Photo: R. R. Jones


As a UCSC graduate student in 1997, Priya Ganguli had not yet settled on a research subject for her thesis when she came upon a strange-looking creek during a field trip. The creek was bright orange, stained with iron oxides draining into it from an abandoned mercury mine. Intrigued, Ganguli decided to find out what else was escaping from the New Idria mine into San Carlos Creek, which flows into a wildlife refuge at the headwaters of the San Joaquin River.
What she discovered not only earned her a master's degree, but helped focus attention on a serious environmental problem.

Ganguli found that mercury, a highly toxic element, was entering the creek from the mine and nearby piles of mine tailings. Spurred by her findings, Ganguli's adviser, professor of environmental toxicology Russell Flegal, launched several new research projects looking at various aspects of mercury pollution.

"Mercury is starting to surpass lead as one of the biggest environmental concerns in the U.S. and throughout the world," says Flegal, one of the world's leading experts on lead and other trace metals in the environment.

As chair of UCSC's newly established Department of Environmental Toxicology, Flegal oversees a unique interdisciplinary program that is addressing a broad range of issues concerning potentially harmful chemicals and microbes in the environment (see sidebar).

His lab's findings on mercury are helping the San Francisco Regional Water Quality Control Board to develop a plan to clean up mercury pollution in the San Francisco Bay Area. Ganguli, meanwhile, is one of two former students from Flegal's lab working on mercury cleanup efforts for the Regional Board.

Mercury, a highly toxic element, was entering the creek from the New Idria mine site. Photo: Russell Flegal

San Francisco Bay consistently exceeds water quality standards for mercury. Some popular sport fish in the estuary contain such high levels of mercury they are unsafe to eat. High mercury concentrations have also been found in failed eggs of an endangered bird, the California clapper rail, that nests in the bay's marshes.

According to Ganguli, some mercury from the New Idria mine, located in San Benito County, may travel down the San Joaquin River and contribute to the contamination of San Francisco Bay. But the largest single source of mercury pollution in the bay appears to be another inoperative mine that Flegal's lab is now investigating.

The New Almaden mining district in the Santa Cruz Mountains near San Jose was once the largest producer of mercury in North America. Mining operations at New Almaden shut down in 1975, and the area is now a Santa Clara County Park. But Flegal's lab is finding that mercury from the mines and associated waste piles is making its way into the Guadalupe River, which empties directly into the southern end of San Francisco Bay.

Most people know mercury as the silvery liquid metal used in thermometers, but it occurs in a variety of other forms. All forms are toxic, but the most dangerous is an organic form of the element known as methylmercury.

A potent neurotoxin, methylmercury readily enters the aquatic food chain and becomes concentrated in the tissues of fish and the animals that eat them. Through the process of biomagnification, concentrations of mercury in predatory fish can be a million times higher than in the surrounding water.

In humans, mercury's toxic effects on the nervous system can lead to serious illness and death. Symptoms include shaking, slurred speech, loss of coordination, and changes in mood and personality. The expression "mad as a hatter" came from the effects on 19th-century hatmakers of the mercury salts used to make felt. In the 1950s, mercury discharged by a factory into Japan's Minamata Bay accumulated in fish and poisoned thousands of people in the fishing village of Minamata, killing more than 800.

But current concerns about mercury are focused on more subtle health effects from exposure to low levels of methylmercury. According to a recent report from the National Academy of Sciences, as many as 60,000 children may be born each year in the United States with neurodevelopmental impairments caused by exposure to methylmercury in the womb. At greatest risk are children whose mothers consume large amounts of mercury-tainted fish while pregnant or nursing.

"What appears to be happening with mercury is the same thing we've seen with lead–the more carefully researchers look, the more they discover subtle health effects from low-level exposure," Flegal says.

Compared with human health effects, much less is known about the effects of mercury on wildlife. In the 1980s, Flegal and his coworkers looked at mercury levels in marine mammals, fish, and invertebrates. They found especially high concentrations in marine mammals, but the effects are still unknown, he says.

"If they were humans they'd be in trouble," Flegal says. "But we don't really know what the effects of mercury are on marine life in San Francisco Bay."

The possible connection between mercury and egg failure in endangered California clapper rails, however, has intensified the pressure to clean up mercury pollution in the bay.

Mercury enters the environment from a wide range of sources, both natural and manmade. It is a trace contaminant of most coal, and emissions from coal-fired power plants are a major source of mercury pollution in many parts of the world. In California, however, historic mining activities have left a toxic legacy of mercury contamination.

Rich deposits of cinnabar, the red ore of mercury, occur naturally in California's coastal mountains. The New Almaden and New Idria mines ranked first and second in output, but many other old mercury mines are scattered up and down the interior flanks of the Coast Ranges.

Much of the mercury those mines produced was used in gold mining operations during the Gold Rush, leaving mercury-contaminated sediments throughout the Sierra Nevada and other parts of the vast watershed that ultimately drains into San Francisco Bay. Miners used mercury to enhance recovery of gold, hauling about 26 million pounds of "quicksilver" in 76-pound flasks into the mountains of California. No one knows how much they left behind or where it is now.

"In the western United States, we are cursed with this mining legacy," says Khalil Abu-Saba, an environmental specialist with the San Francisco Regional Water Quality Control Board.

Abu-Saba, who earned his M.S. and Ph.D. degrees under Flegal, is now working to develop a mercury "total maximum daily load," or TMDL, for San Francisco Bay. A TMDL defines how much of a pollutant a body of water can receive and still meet water-quality standards. The Regional Board then allocates a portion of the total load to each of the known sources of the pollutant, and those sources are required to reduce loads to meet their allocated amounts.

Through the process of biomagnification, concentrations of mercury in predatory fish can be a million times higher than in the surrounding water.
Photo: R. R. Jones

The challenge is to identify and quantify all of the sources of mercury so that cleanup efforts can target the most significant sources. In the late 1980s, Flegal helped the Regional Board set up a monitoring program for trace substances in San Francisco Bay, and his lab still conducts much of the sampling and analysis for the program. As a graduate student, Abu-Saba participated in the monitoring program, so when he began work on the mercury TMDL he knew where to turn for data.

"When I sat down with the numbers and looked at the distribution of mercury in San Francisco Bay, I saw a clear signal leading into the South Bay," he says.

That was surprising, because a substantial amount of mercury enters the north end of the bay through the Sacramento-San Joaquin Delta from old gold and mercury mining sites that drain into the Central Valley. So Abu-Saba asked Flegal if his lab could take a look at mercury contamination in the New Almaden region. Martha Thomas, an undergraduate working in Flegal's lab, and graduate student Christopher Conaway took on the project.

"They produced some of the first measurements of methylmercury in sediments from the Guadalupe River watershed, and that gave us the smoking gun we needed to show that New Almaden is the biggest ongoing source of mercury pollution in the bay," Abu-Saba says.

Ongoing sampling in the Guadalupe River shows a lot of mercury coming down the river from the New Almaden mining district, Conaway says.

"In some places, people have even been able to pan liquid mercury out of the sediments," he says.

Abu-Saba's draft report calls for a major reduction in the mercury load coming from the Guadalupe River. The Santa Clara Valley Water District, as well as the Santa Clara County Parks, would be primarily responsible for achieving that reduction, he says.

The process leading to formal adoption of a total maximum daily load for mercury will take several years, but Abu-Saba hopes to get cleanup efforts in the Guadalupe River watershed started before then. The Santa Clara Valley Water District and the U.S. Army Corps of Engineers are currently engaged in a massive flood-control project on the Guadalupe River, which Abu-Saba sees as an opportunity to remove mercury-contaminated sediments.

"We have been working closely with them, and I do believe we can remove large amounts of mercury from the watershed in the short term," he says.

In the long term, preventing additional contamination from New Almaden will require controlling erosion and runoff from the huge piles of mine tailings, which cover large areas around the mines. Ganguli is monitoring the effectiveness of such remediation efforts at another old mercury mine, the Gambonini mine, in Marin County.

Investigations of the New Almaden and New Idria mine sites are only one aspect of the ongoing mercury research in Flegal's lab. Other projects include measuring mercury in air and rainwater to see how much mercury pollution in the Bay Area comes from the atmosphere; looking at petroleum products as potential sources of mercury; and studying how mercury changes from one form to another in the environment and how it cycles between the water and the sediments in San Francisco Bay.

According to Flegal, many unanswered questions remain. "Our understanding of the cycling of mercury in the environment is about where our understanding of lead was ten years ago, so we're way behind," he says.

–Tim Stephens

Environmental perils: An interdisciplinary approach

Environmental Toxicology Department chair Russell Flegal Photo: R. R. Jones


Heavy metals, pesticides, dioxins, pathogenic bacteria–a dizzying array of pollutants and harmful organisms has made its way into the environment, raising disturbing questions for our industrial society. Are there toxic chemicals in our drinking water, our food, the air we breathe? What level of exposure is harmful to human health? How are pollutants affecting wildlife and complex ecosystems?

UCSC's Department of Environmental Toxicology, established in the summer of 2000, is addressing these issues through scientific research, teaching, and collaborations with state and federal regulatory agencies. With a growing range of interdisciplinary research programs, the department builds on UCSC's recognized strengths in environmental research.

The department's faculty are widely recognized for their work on toxic heavy metals and harmful bacteria. Ultimately, the results of their research may lead to new methods for controlling environmental hazards and for counteracting the health effects of pollutants.

"We want to identify the sources of toxicity in the environment and understand how they become a threat to organisms, including humans," says Russell Flegal, who chairs the new department.

The department, which offers graduate programs leading to M.S. and Ph.D. degrees and undergraduate courses in environmental toxicology, fills a distinctive niche, Flegal says. Most other toxicology programs are associated with medical schools and focus primarily on human health, while UCSC's program focuses on all types of organisms, including humans.

In addition to Flegal, who studies how human activities affect the cycling of trace elements in the environment, the department includes:

Assistant Professor Karen Ottemann, who studies how pathogenic bacteria respond to their environment and infect their hosts;

Associate Professor Donald Smith, who studies the biological effects of heavy metals and is involved in efforts to improve treatments and reduce human exposure to lead;

Assistant Professor Zhiwu Zhu, who studies the molecular mechanisms involved in the regulation of metal ion concentrations inside cells.

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