A reader requests more information regarding mercury and tuna:
I just had tuna last night. Tell us more about tuna-induced mercury poisoning, please!
Consumer Reports in 2015 gives a quick summary:
Mercury can damage the brain and nervous system, especially when exposure occurs in the womb. That’s why we recommend that pregnant women not eat tuna and any other high-mercury fish, such as shark and swordfish. High-mercury seafood can pose health risks to other vulnerable groups as well. So we also recommend that young children, women of childbearing age, and anyone who eats 24 ounces or more per week of any fish limit their tuna consumption, especially those kinds that are high in mercury, such as yellowfin and other species used in sushi.
The importance of that advice was underscored earlier this year by a study that found that mercury levels in yellowfin tuna had increased at an annual rate of almost 4 percent from 1998 through 2008. Rising mercury levels in oceans because of pollution from coal-fired power plants and other industrial sources are to blame, the study suggested.
More recently there has been good news, although tempered by the election of President Trump, as reported in November 2016 by Scientific American:
Image Credit: Oceana
Levels of highly toxic mercury contamination in Atlantic bluefin tuna are rapidly declining, according to a new study. That trend does not affect recommended limits on consumption of canned tuna, which comes mainly from other tuna species. Nor does it reflect trends in other ocean basins. But it does represent a major break in the long-standing, scary connection between tuna and mercury, a source of public concern since 1970, …
The new study, published online on November 10 by Environmental Science & Technology, links the decline directly to reduced mercury emissions in North America. Most of that reduction has occurred because of the marketplace shift by power plants and industry away from coal, the major source of mercury emissions. Pollution control requirements imposed by the federal government have also cut mercury emissions.
Bluefins are long lived, giving them a lot of time to absorb mercury, so this is a surprise, according to the article.
“We could as easily have expected it to take a century” for the fish to show signs of recovery, Fisher remarks. The contrary finding “tells me we don’t just have to wring our hands about the high level of mercury in these fish. There is something we can do about it and get pretty quick results.” [Study co-author Nicholas Fisher, a marine biogeochemist at Stony Brook University.]
It’ll be fascinating to hear why the bluefins are not as highly contaminated as expected. Have they evolved a way to excrete the mercury, or otherwise avoid it?
