Life in Heavy Metal
Invisible to the naked eye and ubiquitous like air, mercury is among America's most persistent environmental contaminants. Chemistry Professor Janina Benoit and her students mine the sediments to find out why.
By Jayne M. Iafrate
Somewhere west of here—Asia, Minnesota, the Berkshires; it hardly matters where—a plume of smoke rises into the sky. High and thick, its willowy trailhead fades as upper-level winds begin to carry it east, far from its coal-fired power plant or manufacturing facility origins. Every day the remains of industry drift toward New England and settle quietly all around us—in Boston Harbor, on the Dimple and even in the vernal pools that surround the Wheaton campus. Where mercury ends its airborne journey, Chemistry Professor Janina Benoit picks up the trail.
Benoit studies how mercury interacts with life in the aquatic environment. Specifically, she wants to know more about how monomethyl mercury (MMHg), the toxin formed when elemental mercury meets bacteria, behaves in coastal sediment organisms—benthic macrofauna— before it is consumed by the fish that eventually end up on our dinner plate. If she is able to answer some of her nagging questions about the cycle of MMHg in the environment, governments will be better able to manage coastal fisheries and to control human exposure to this deadly neurotoxin.
To help answer those questions, the Massachusetts Institute of Technology Sea Grant program awarded Benoit and her research partner, Professor David H. Shull of Western Washington University, nearly $100,000 to collect and analyze coastal sediment samples during the next two years. Along with Wheaton student researchers, they will amplify their previous study, which revealed "significant production and accumulation" of MMHg in Boston Harbor sediments, by learning how MMHg moves through the benthic food web. They hope the new study will result not only in better policy, but also in the identification of a sentinel species— an aquatic canary in a coal mine—that will alert us to changes in mercury levels in the environment.
Benoit will spend this spring fabricating testing equipment and preparing her lab for the analytical work ahead. Sampling of sediments will start this summer and analysis will take place at Wheaton through the 2006-07 academic year. In spring 2007, the researchers will collect deposit-feeder digestive fluid for study the following summer. By February 2008, they hope to publish their results. "Sedimentary production is a major source of MMHg in a number of ecosystems," Benoit explained, "and consumption of marine fish represents the primary route of human exposure."
Mercury contamination is among America's most persistent pollution problems today. Although mercury does occur naturally, it enters our aquatic ecosystems primarily through waste-chemical spills, discarded batteries, thermometers and thermostats, for example—and through the air, where it can remain for up to a year before falling to the earth. According to the U.S. Environmental Protection Agency (EPA), 48 tons of mercury are spewed from America's coal-powered utility plants, and between 1,800 and 3,700 pounds of mercury each year are deposited from the air to the land and water in Massachusetts alone.
In March 2005, the U.S. government first began to regulate mercury emissions. The EPA issued the Clean Air Mercury Rule, which seeks to reduce mercury emissions from coal-fired power plants by 70 percent in 2018. That wasn't enough, according to a lawsuit filed two months later against the EPA by the attorneys general of 11 states, including Massachusetts, who believe that the EPA rule establishing a cap-and-trade system for regulating mercury emissions from power plants will delay "meaningful emission reductions for many years and perpetuate hot spots of local mercury deposition, posing a grave threat to the health of children."
Mercury—the liquid metal we remember from our childhood thermometers—is toxic, but it becomes even more hazardous in its methylated form. When mercury generated from coal-powered plants falls from the air into bodies of water, it is converted into methyl mercury by bacteria in the sediment layers. These organisms produce MMHg, which is taken up by benthic macrofauna, which are in turn eaten by fish. Methyl mercury becomes more concentrated in the tissues of organisms as it moves up the food chain, so it can reach very high levels in predatory fish like tuna and swordfish. Then it comes to us.
Since 2000, nearly every state and the U.S. government have issued fish consumption advisories that inform women who may become pregnant, pregnant women, nursing mothers and the parents of young children "how to get the positive health benefits from eating fish and shellfish, while minimizing their mercury exposure." The danger is that methyl mercury is able to cross the blood-brain barrier, a membrane that normally protects the brain and the central nervous system from toxins.
For fetuses, infants and children, the primary health effect of methyl mercury is impaired neurological development. Impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skills have been seen in children exposed to methyl mercury in the womb, according to the Centers for Disease Control (CDC). While healthy adults are less vulnerable, the CDC has studied reports of methyl mercury poisoning in which victims have reported impairment or disturbances in peripheral vision, sensations, coordination of movements, speech, hearing and walking.
For environmental scientists like Benoit, any contaminant is cause for concern and study. Her interest in science stems from a love of nature, a passion nurtured by her father.
"My dad was an environmental scientist long before the term was coined," Benoit said. "He had a Ph.D. in zoology, but developed expertise in chemistry, limnology, ecology and natural history throughout his long career. He taught me (and my brothers and sisters) to respect and appreciate nature."
Benoit was introduced to mercury after she completed her master's degree in oceanography at the University of Connecticut. What appeals to her about studying mercury is that it is a global contaminant that requires a "big picture" viewpoint.
"My research on mercury biogeochemistry requires me to draw on a broad range of scientific disciplines," she explained. "One thing I love about being at Wheaton is that it allows me to move beyond interdisciplinarity within the science division to work across divisions through collaboration [Benoit is working with psychology professor Grace Baron on a study of the relationship between mercury and autism.] and connected courses."
That connectedness of disciplines extends far beyond Benoit's research to that of her students. During the January break, biology major Lyndsey Shorey '06 and pre-med student Hilary Macgruder '09 worked in the lab with Benoit to study how mercury behaves in the environment. Shorey looked at how carbon sources affect mercury methylation by bacteria, while Macgruder measured the levels of mercury in leaf samples she collected in one of Wheaton's vernal pools last fall. She wants to know if leaves transport mercury from the air to vernal pool organisms.
"I think of all the things I eat, and I want to know where the mercury might be," Macgruder said.
