June 24, 2010 – Researchers have studied methylmercury’s neurotoxic effects for decades, but recently scientists have connected this form of mercury—found in fish that people eat—to heart disease. A new computer model that considers these cardiovascular effects finds that cutting mercury pollution by 10% could save the United States millions of dollars in health costs—a benefit that regulators should consider, the authors say (Environ. Sci. Technol. DOI:10.1021/es903359u).
Although a handful of epidemiological studies have linked methylmercury to heart disease, the connection remains weak, experts say, because these studies relied on small sample sizes and weren’t comprehensive enough for a definitive conclusion. But a team from the Harvard School of Public Health wanted to estimate the healthcare savings of cutting methylmercury exposure nationwide given this possible heart disease link.
Harvard risk specialist John Evans and his colleagues used data from published studies on methylmercury’s neurotoxic and possible cardiovascular effects and fed it into a Monte Carlo model—a standard technique used to evaluate complex systems—to make their estimate. They first calculated all likely mercury exposure levels for people in the U.S. based on parameters such as diet and gender. Because data on total mercury concentrations in people’s hair and blood is more reliable than current methylmercury exposure data, the researchers used mercury as a proxy for methylmercury in their model. Next the researchers assessed the health-related costs, such as medical bills and lost wages, at each exposure level.
With these cost estimates in hand, Evans and his colleagues then calculated the savings created by reducing a person’s mercury exposure. For a person in the highest exposure group, removing 1 µg of mercury from the daily diet — equal to the daily dose that a person receives from dental fillings—led to a $116 per day savings. When the researchers looked across all exposure groups, they estimated that cutting mercury intake by 10% could save the U.S. more than $800 million in health costs each year.
But Evans cautions that this model is “a thought experiment” intended to raise awareness that cutting methylmercury emissions could lead to cardiovascular benefits. Fitting all the epidemiological data together for the cost calculations led to immense uncertainties, he says, because the few cardiovascular studies that do exist do not agree on the strength of the connection to methylmercury. Also this model does not address the cardiovascular benefits of eating fish, the main source of mercury intake, Evans says. He hopes that government organizations such as the Environmental Protection Agency will convene a panel of toxicology and epidemiology experts to better evaluate the existing studies in this model.
A more complete evaluation should also address the economic costs of further cutting methylmercury emissions, says Ari Rabl, formerly of the School of Mines in Paris and now an independent environmental consultant. The pollutant’s major anthropogenic sources include power plants, which would bear high costs to reduce mercury emissions. But the model is a good first step, Rabl says: It’s an “example of the kind of study needed to help governments make more rational decisions.”