WHAT DOES the actor Jeremy Piven have in common with over 300 million gallons of sludge, recently spilled from the waste pond of a coal-fired power plant in Tennessee?
Both have moved mercury from a lower rung in the Periodic Table of the Elements back into the headlines. Piven recently withdrew from the Broadway production of "Speed the Plow," citing health problems associated with mercury poisoning resulting from eating sushi twice a day over many years. Many have cast doubt on Piven's illness and suggest he is attempting to use mercury poisoning as an excuse to step down from a role he didn't wish to play.
Whatever the truth, the stories about Piven, and the sludge - a byproduct of coal combustion that contains a diverse family of heavy metals - have reignited the debate about the real and imagined dangers of mercury.
What are the facts known to date? Unlike contaminants such as DDT and PCBs that were synthesized in the last century, mercury is natural and present at high concentrations in coal. Current estimates find that human release of mercury, particularly through the combustion of coal, has tripled the amount of mercury entering the atmosphere in the last century and a half, and is likely to continue to increase. And mercury is unusual in that it can exist in numerous forms, some quite volatile, that facilitate its movement through air, land, and water. Thus the mercury released today from a power plant in Ohio or China is likely to land almost anywhere on Earth.
One form of mercury, methylmercury, is capable of accumulating in aquatic species, especially with the highest levels in the largest and oldest predatory fish - like tuna, swordfish, king mackerel, and sharks - to levels 10 million times that of the water in which they swim. And while consumption of seafood is the largest source of methylmercury to humans, seafood is also a great source of omega-3 fatty acids that lower the risk of cardiovascular disease and promote neurological development.
To complicate this issue, mercury toxicity varies among population groups. For example, the US Environmental Protection Agency and the World Health Organization have stated that mercury is of greatest risk to children and fetuses, as developing central nervous systems are particularly susceptible to the neurotoxic effects of this metal.
So balancing the health benefits of eating fish must be carefully weighed on an individual basis. A committee convened in 2007 by the Institute of Medicine of the National Academy of Sciences recommended that a healthy middle-age male, such as Piven, could consume two 3-ounce servings of seafood per week, and, if more than that, to vary the types of seafood. Pregnant or nursing women can consume the same amounts of seafood but should specifically avoid swordfish, king mackerel, shark, some tuna, and other predatory fish. Clearly, Piven was exceeding the advice of this report.
However, the report also stated that information on mercury in seafood has been "fragmented," and recommended that an interactive website be designed that could help consumers determine their personal risk/benefit profile based on gender, age, pregnancy or possibility of becoming pregnant, or breastfeeding, and risk of coronary artery disease. This same report also noted that while much is known about mercury toxicity, "there is [also] uncertainty about the potential for subtle adverse health outcomes."
With these concerns and recommendations, it is important to note that, unlike PCBs and DDT, which have declined in humans and seafood during the past several decades, mercury continues to be a concern. And unlike DDT and PCBs, which have been banned in most countries, coal combustion (the leading industrial source of mercury to the environment) continues and may even increase in the future.
Coal is likely to be part of our energy portfolio for the next several decades. Many in government (including President Obama) have suggested that the United States, which has 25 percent of the world's coal reserves, should increase the use of coal for energy, particularly through application of "clean coal" technologies. In addition to the implications of strip mining and other environmental concerns, we should pay great attention to the impact that increased use of coal could have on the release of mercury to the environment. If we don't, we will see more stories like Piven's and about the mismanagement of the spoils of coal combustion.
Carl Lamborg and Christopher Reddy are environmental chemists specializing in the study of contaminants in the environment at the Woods Hole Oceanographic Institution.