After a contentious election, those of us who enjoy tuna fished from the Gulf of Maine received some very refreshing news. In a recent report covered by several news outlets, including the Washington Post and Maine Public, Nicholas Fisher of Stony Brook University in New York has shown that the level of mercury in tuna from the Gulf of Maine has been declining by 2 percent a year. The decline is welcome news given that mercury acts as a neurotoxin that can cause muscle weakness, loss of peripheral vision, lack of coordination, impairment of speech, hearing and walking. Mercury exposure in infants or young children can negatively affect brain development as well.
What may not be acknowledged by many, however, is how mercury makes its way into tuna in the first place. Although small amounts of mercury are naturally released during the weathering of rocks, the major source of mercury in tuna fish is the combustion of coal and other fossil fuels. As these fuels are burned, mercury is released into the atmosphere, where it travels with the prevailing winds in particulate, elemental or gaseous forms. The airborne mercury eventually mixes with dust, rain or snow, and it settles to the earth.
When mercury reaches the ground, it enters the water and microbes convert the mercury to methylmercury. Methylmercury is readily taken up by plants at the base of aquatic food webs. When small fish eat these plants, the mercury accumulates in them. Similarly, when predators up the food chain eat these fish, mercury begins to accumulate in them as well. This results in increasing concentrations of mercury at each level of the food web. Because tuna are carnivores, typically at the top of an oceanic food web, they build up high concentrations of mercury from their food, a perverse example of “you are what you eat.” We also increase our risk for mercury poisoning whenever we eat tuna and other carnivorous fish.
The mercury contaminating tuna in the Gulf of Maine historically has come from coal-fired plants and other industrial activity in the Midwest that has been blown across America by the prevailing winds. Since the early 2000s, about two dozen states have placed strong limits on mercury emissions from power plants, and those regulations have had a positive impact on Maine and its waters. In 2011, the EPA finally adopted the first federal limits on mercury emissions from power plants, and the Supreme Court earlier this year refused to block that rule.
As Fisher’s research has shown, declines in mercury emissions are closely tied with reductions in mercury contamination in tuna. Indeed, he noted that “the decline is almost in parallel with declines in mercury emissions from coal-fired power plants and the decline of mercury in the air. It appears that the fish are responding almost in real time.”
But these gains in mercury reduction could be erased, as President-elect Donald Trump has nominated Scott Pruitt to head the EPA, an agency to which Pruitt has been hostile. Trump has often touted a move to “ clean coal” (a misnomer) and the need to undo environmental regulations to grow jobs. For Maine, such changes would be incredibly short-sighted and only serve to reverse progress made in reducing the levels of mercury in our waters.
We urge Maine residents to write and call Sens. Angus King and Susan Collins and Reps. Chellie Pingree and Bruce Poliquin to urge them to carefully scrutinize the appointment of Pruitt and forcefully reject any attempts to weaken the EPA or the Clean Air and Clean Water acts. The short-term benefit to polluting industries is not worth the return to environmental degradation, particularly for a state like Maine that has a strong and growing natural resource-based economy. We have a responsibility to preserve and protect the natural beauty surrounding us, and we can make a difference by simply making a call.
Emily Craig is a junior in the School of Marine Sciences at the University of Maine in Orono. For her senior thesis she plans to study how changes in the atmospheric deposition of pollutants will affect Maine’s aquatic food webs. Paul Rawson is an associate professor of marine science at UMaine, where he teaches a course in marine ecology and human impacts.