Large drop in bluefish mercury levels suggest fish eaters are consuming less of the toxic metal – and that U.S. reductions are working
Mercury levels in bluefish caught off the U.S. Atlantic coast dropped more than 40 percent over the past four decades thanks to federal restrictions on coal emissions, according to a new study.
This is good news not only for bluefish but for the entire predator fish population in the Mid-Atlantic. And it's better news for people fond of eating the tasty fish, often served broiled or baked, as it suggests that mercury reductions due to coal-fired plant emissions crackdowns in North America have quickly led to less contamination in marine life.
"This is an important study ... this is the type of work that we need to encourage policy makers to support clean-coal technology," said Katlin Bowman, a postdoctoral scholar at the University of California's Department of Ocean Sciences who was not involved in the study.
Coal-fired plants are big mercury contributors to the atmosphere – where most emission pollution gets dumped – and the ocean, where those pollutants eventually settle.
Efforts over the past few decades to reduce stack emissions has led to quick and dramatic improvements in local air quality. But researchers and regulators assumed any change in ocean conditions and fish mercury contamination would take at least a century to see, given the vastness, said senior author of the study Richard Barber, a professor emeritus of biological oceanography at Duke University.
That assumption appears to be wrong, he said.
"What the EPA decides clearly makes a difference as to how much mercury people consume," Barber said.
Coal, bluefish mercury levels drop in tandem
Barber and colleagues tested the mercury levels in the muscle of adult bluefish collected in 2011 off the North Carolina coast and compared it with similar testing from 1972.
Concentrations decreased 43 percent. The drop is similar to reductions of mercury observed in "atmospheric deposition, riverine input, sea water, freshwater lakes and freshwater fish across northern North America," Barber and colleagues wrote in the study published this month in the Environmental Science and Technology journal.
Five studies that Barber examined all show a "tight" correlation between the amounts of mercury emitted from coal plants and concentrations in fish.
Nothing, he said, suggests that "there is not a tight coupling between deposition and fish."
Coal burning is considered the major contributor of mercury in today's environment. Power plants send mercury into the atmosphere that is then deposited in oceans, mostly through rainfall.
A report last year that examined emissions from the top 100 U.S. electric power producers found a 50 percent decrease in mercury emissions from 2000 to 2012.
With evidence that aquatic wildlife are, at least in part, responding to such measures, "there is increased incentive to document and predict future changes in mercury concentrations in marine fish, particularly those of economic value, " Barber and colleagues wrote.
President Obama has attempted to further restrict emissions of mercury and other toxics from coal-fired plants through the Clean Air Act, but the Supreme Court blocked the ambitious initiative last month.
Barber and colleagues wrote that increasingly stringent measures on coal plants could drive mercury levels in fish even lower but cautioned that, since mercury travels the globe on wind and air currents, such reductions could be "overwhelmed by a continued increase in mercury emissions from Asia."
Bowman also cautioned that, even though bluefish have had steady declines over 40 years, there is still a large quantity of legacy mercury that can be re-emitted from the environment, so the trend could change.
To eat or not to eat
Popular to catch due to their aggressive fight and to eat, bluefish are a migratory fish and can be found from Maine to Florida in the Atlantic. Recreational anglers and commercial fleets harvest roughly 13 million pounds and 5 million pounds a year respectively, said José Montañez, a fishery management specialist with the Mid Atlantic Fishery Management Council.
Schools of fish migrate together in the spring to an area called the Mid-Atlantic Bight, the shelf waters from Nantucket Shoals off Cape Cod, Massachusetts, then head south to Cape Hatteras, North Carolina.
They're voracious eaters, feeding on a wide variety of ocean creatures.
Fish high in the marine food chain such as bluefish are considered the major source of mercury exposure in the United States. Studies have linked pregnant women's high mercury consumption in seafood to reduced IQs and memories and other neurological impacts in their children.
Among coastal U.S. coastal areas, women along the Atlantic coast were recently shown to have the highest average mercury blood levels. Bluefish have long been considered a species with pretty large mercury loads compared to other commercially caught fish.
However, there are benefits to eating fish. Research has shown that fish consumption provides vital nutrients, Omega-3 fatty acids and protein, for fetal brain growth, and that children's IQs increase when their mothers had eaten low-mercury fish.
The study could "potentially impact demand for the product [bluefish]," Montañez said.
Health officials have long struggled with how to balance the benefits and downsides of eating fish.
"It's really difficult to tell. We all judge risk benefit info differently. I know people that will not feed a single bluefish to their kids," Montañez said. "Then I know people who smoke it and eat it all year long and they're both aware of the potential problem with contaminants."
Last summer the U.S. EPA and FDA made major changes in their advice to pregnant and breastfeeding women by recommending consumption of at least 8 ounces of low-mercury fish per week.
Bowman said a good next step would be to examine other fish species to ensure that the decline is connected to decreasing mercury emissions and not driven by some change in the physiology or feeding patterns of bluefish.