The New York Times has a nice investigative piece on mercury levels in your local urban sushi parlors that briefly restored my faith in mainstream science journalism. The Times performed what you might call a guerilla science action, hiring a pair of local professors to help to analyze bluefin tuna samples from 20 sushi places around Manhattan. Every city should do this. It’s a great way to support local science labs, buying them lunch and funding research at the same time.
Researchers from Rutgers and Robert Wood Johnson Medical School found 5 of the 20 metropolitan restaurants serve tuna spiked with objectionable levels of mercury, according to standards set by the US Federal Drug Administration and Environmental Protection Agency. These results should catch the attention of federal authorities, because the idea of tuna fish poisoning the human bloodstream is becoming commonplace and unavoidable. According to the new research, adults should limit themselves to one meal of red tuna sushi every three weeks. That’s a serious cutback for some.
Mercury in seafood accumulates in muscle tissues of top predators like swordfish and bluefin tuna from prey contaminated by methylmercury from coal burning energy plants. The mercury bio-accumulates, ultimately, in people.
The questions for seafood society come down to a few. How does mercury harm people? What evidence is there? And, inevitably, how many pieces of sushi can I eat exactly? I’ll add one more. Why are pregnant women advised against mercury, but no one else?
At high doses, the effects of mercury are acute and sometimes lethal. The link between high levels of mercury and CNS damage is clear in the Japanese courts. The infamous Minimata Disaster in Japan consisted of 27 tons of mercury dumped into Minamata Bay by Chisso Corporation between 1932-1978. Some of the Minimata cases were still in court in the early 90′s. Human symptoms included numbness in the limbs, involuntary movements, uncontollable shouting, blurred vision, and unconsciousness. If any of this sounds like your boss, tell them to cut down on the sushi!
The most relevant dosage of mercury for sushi eaters would be a moderate daily dose from a single source like canned tuna. Apparently, this level of mercury can induce a “fish fog” that causes problems sleeping, focusing and studying. This is the claim of graduate student Luke Lindley of Stanford University, who was once accustomed to eating canned tuna fish every day for lunch. He tested his hair one day to find he was mercury contaminated. As I understand it, he kicked the habit and recovered. Larry Wheeler describes the story in detail in an excellent and well-illustrated piece at USA Today. This idea of detoxification seems counter to the idea of bioaccumulation and long residence times for heavy metals, but people embark on these programs.
Pregnant women are advised against mercury because of potential birth defects to the developing neurosystem of the unborn fetus. Adults are not warned against mercury consumption because they have greater mass, so toxic levels are theoretically unattainable via normal seafood consumption. It has also been stated the benefits of fish oil consumption outweigh the risks or mercury poisoning.
Past comments here at DSN have gone so far as to say that obstetricians advise women against fish consumption mostly because of liability issues, rather than any perceived danger to the fetus. Doctors advise pregnant women because they must. Much of the conflict of opinion about mercury is centered around actionable levels. Recent studies found one fourth of New Yorkers have elevated levels of mercury, but critics argue that the standards are too low, and too reactionary. I am trying hard to be balanced here.
According to New York Times, young children and pregnant and breast-feeding women should avoid high-mercury species like Chilean sea bass, orange roughy and tilefish. The first two are not sustainable fisheries, anyway, because the fish are long lived and slow to reproduce.
A brochure called “Eat Fish, Choose Wisely,” suggests you eat no more than two six-ounce servings a week of low-mercury varieties like cod, mullet, scallops and canned light tuna, and no more than five such servings of very-low-mercury fish like clams, shrimp, tilapia and salmon.
This New York Times study supplements others by a grassroots non-profit spin off of the the Sea Turtle Island Restoration Network called Got Mercury?. The group sampled sushi in Los Angeles, Chicago, and San Diego in 2006. Chicago Times followed up with an investigative piece. Deep Sea News followed the story last July in a slightly controversial piece called “How Safe is your Sushi?” and a follow up piece on mercury levels in fishermen. Mark Powell from Blogfish also reports on the swordfish side of the story here.
The methods for these guerilla science studies are pretty simple. Dine in a few random sushi spots, pick up a few orders of maguro tuna, and bring them back to the lab for analysis. Badda bing. Citizen science. Ocean revolutionary. That’s you. So, how safe is your sushi? More and more its safe to assume its polluted.