In my youth, I was an avid fisherman who listened to heavy metal music. But today’s anglers catch heavy metal on a hook while singing the blues, because many of the fish commonly taken for sport and food in New Hampshire and Vermont now contain toxic levels of mercury.
Most mercury released into the environment comes from coal-fired power plants, incinerators, industrial boilers, and plants that manufacture chlorine. About 60 percent of the mercury pollution that reaches the Northeast is borne on westerly winds from coal-fired power plants in the Midwest and Pennsylvania. Mercury in lesser quantities also arrives in air pollution from abroad and from regional sources.
In some places, such as the lower Merrimac River watershed in southeastern New Hampshire, rivers and lakes now contain levels of mercury that are significantly higher than the natural levels. Other mercury “hotspots” include the Rangeley Lakes region of Maine, the far northern and southern waters of Lake Champlain, and the upper Connecticut River north of Barnet and Monroe. Nearly half of the surface waters in the Northeast now contain levels of mercury that are above the U.S. government’s threshold for safety.
Mercury travels through the atmosphere as a gas, as tiny, airborne particles, and as particles incorporated into rain and snow. Once elemental mercury falls to earth, it is transformed by bio-chemical reactions into highly toxic methyl mercury. Methyl mercury is accumulating locally at two to four times the rate that would normally occur in nature. Among fish, high concentrations of this substance can lower the success of spawning, kill developing embryos, cause slow and abnormal growth, and alter behaviors such as schooling.
Algae in lakes and rivers absorb mercury and are then consumed by aquatic insects, crustaceans, snails, and minnows or other small fish. These are in turn eaten by sunfish, perch, and bass. The big, carnivorous predators at the top of the finny food chain, including adult northern pike, walleye, and lake trout, hunt mostly fish and other animals. Each time a predator eats, it absorbs the mercury contained in its prey. Top predators accrue the sum of mercury that has been concentrated in their food supply. For this reason, larger predaceous fish may contain very high levels of mercury.
Eating too much fish that is contaminated with mercury can cause damage to the human kidneys, liver, and central nervous system. This is most true among fetuses, infants, and the small children of mothers who ate contaminated fish while pregnant. The FDA and the EPA recommend that pregnant and lactating women, infants, and young children limit their consumption of fish to those species that are safe to eat.
Some of our most popular freshwater sport fish are contaminated with mercury, including walleye, northern pike, white perch, and lake trout. Of even greater concern for public health is that many favorite panfish, including yellow perch, brook trout, and bass, often contain high levels of mercury. This a hardship for families who like to catch fish to supplement their food supply and also a challenge for native peoples whose cultural identities and subsistence activities are inextricably linked to the traditions of fishing and hunting. When it is no longer safe to catch and eat fish from a local lake or river, yet another connection between ourselves and the natural world is severed.
Mercury contamination of fish is ironic because, toxins aside, fish (especially salmon) contain beneficial omega-3 fatty acids that make them an excellent part of a healthy diet. This diet can ward off heart disease, slow the advance of early Alzheimer’s, and decrease the chance of contracting diabetes, cancer, and depression. Pregnant women who eat safe fish in moderation may enhance the fetus’s brain development, encourage good eyesight, and diminish the possibility of premature births of low weight.
The hopeful news is that clean air laws require that mercury emissions be contained by installing advanced air pollution control technology on older power plants when they are upgraded. Michigan aims to reduce mercury released from coal-burning power plants by 90 percent within a decade. Since 1998, mercury emissions in New England and eastern Canada have been cut by more than half and levels of mercury in the lakes of Vermont and New Hampshire are slowly dropping. If these trends hold, lovers of fish and fishing may be able to cast their hopes toward a brighter future.
Meanwhile, health experts recommend eating not more than two servings each week (a total of 12 ounces) of safe fish, meaning one of our local fish species that is less prone to mercury concentrations and has not been caught in a mercury hot spot area. To find our where your favorite fish (and fishing hole) fits in the larger mercury picture, visit www.epa.gov/region1/eco/mercury/newengland-fish.htm.