Mercury in seafood may once again be on the rise, according to new research published this month in the journal Nature.
In the study, researchers looked at methylmercury, a toxic form of mercury linked to cognitive disorders and developmental delays in children. Over the past several decades, regulation efforts have steadily decreased the amount of human-caused mercury flowing into the oceans and into our seafood. But researchers are warning that climate change has the potential to make the neurotoxin a public health concern once again.
To model the effects of temperature on methylmercury concentrations in fish, the researchers used decades of data on two commonly consumed species, spiny dogfish and Atlantic cod, to build a computer simulation. They discovered that as temperatures rose over time, so too did the amount of food the fish ate. “When you warm [fish] up, they eat more.” Amina Schartup, the lead researcher on the study, told WBUR’s Angus Chen.
There’s nothing inherently wrong with hungry fish. But methylmercury, which is found in ocean water, becomes concentrated as it moves up through the food chain from filter feeders and plankton to larger and larger fish. By the time it reaches, say, a top predator like a bluefin tuna, the neurotoxin can accumulate to amounts that can negatively impact human health. And with fish eating more, more methylmercury is entering the food chain and accumulating at the top.
When the team applied their simulation to Atlantic bluefin tuna, they had similar results. Their model predicted that, by as early as 2030, mercury in tuna could jump to levels not seen since the 1970s, before mercury pollution regulations were put in place—levels well beyond the mercury limits recommended for seafood by the Environmental Protection Agency.
The model also showed that climate change may influence mercury in more subtle ways. During the 1970s, the Gulf of Maine suffered a herring fishery collapse, compromising a major food source for spiny dogfish. In the absence of herring, spiny dogfish switched to squid, an animal higher up in the food chain. Researchers found that this change in diet was substantial enough that methylmercury concentrations more than doubled in spiny dogfish.
While sustainable fishing practices can prevent another fishery crash like the one in the 1970s, previous research shows that a few degrees of warming can be enough to drive marine animals out of their natural range. This could lead to dietary changes with effects similar to what was seen in the herring collapse.
“[This is] an important study, showing how the quality of our seafood is intimately connected to a healthy, balanced ocean and that human behaviors—fishing and climate change—directly affect the contamination profiles of that seafood,” Anela Choy, an assistant professor at the Scripps Institution of Oceanography who wasn’t involved in the study, told Ed Yong at The Atlantic.
The study’s findings suggest that, in the presence of global warming, regulations alone won’t be enough to shrink the amount of methylmercury in seafood. What’s more, current regulations on the coal industry, which limit mercury release, could be overturned. The study authors emphasize that a combination of approaches will be necessary to tackle mercury poisoning. “Even if we maintain mercury emissions at a constant rate, we’ll see an increase in mercury levels in tuna just due to seawater temperatures,” Schartup told Yong.