Conscientious eaters are avoiding certain tuna species (like the bluefin), knowing that it could be extinct in a few years if rampant overfishing is not put to a halt. However, if that doesn't already deter you, then consider this: a recent study has found that certain tuna species (ones favoured by high-end sushi restaurants for their firmer flesh) actually had higher concentrations of mercury than your typical supermarket canned tuna. Consider also another study which showed that one-third of all mercury exposure comes from tuna - well, it's enough to make anyone have second thoughts. Read on to see which tuna species to avoid and why.The study found that on average, all the tuna species examined had mercury levels that exceeded the daily level of consumption recommended to be safe by the Environmental Protection Agency. But the worst offenders were bluefin akami (dark red) tuna and all bigeye tuna, which contained mercury levels higher than other species usually found in grocery stores and restaurants as well (bluefin or fatty toro tuna and yelllowfin).
Fish DNA "fingerprinting" used for first time, revealing sushi fraud too
Interestingly enough, the study used a new DNA barcoding technique to identify unknown samples of fish, allowing scientists to match and compare measured mercury levels between the different species - something that previous studies could not reliably do.
"[This is the] first study where every sample of tuna that we examined was barcoded so that we know for sure what the specie is, there was no guess work," says study researcher Prof. Joanna Burger of Rutgers University.
Coincidentally, the same technique has uncovered sushi 'fraud': some sushi restaurants were substituting the similar-tasting fish escolar (which causes diarrhea once consumed) in place of tuna. Tsk.
Does it mean that people will stop eating tuna sushi immediately? Probably not. But the study's authors hope that the findings will lead to better labelling so that consumers can make informed choices.
"So far, the U.S. does not require restaurants and merchants to clarify what species they are selling or trading, but species names and clearer labeling would allow consumers to exercise greater control over the level of mercury they imbibe," said Jacob Lowenstein, a graduate student with the American Museum of Natural History in New York, who also took part in the study.
Mercury, mercury, everywhere
Unfortunately, mercury is a near-ubiquitous toxin that accumulates up the food chain and damages the brains, lungs and kidneys - it's in our amalgrams, in our high fructose corn syrup, even in mascara. It is especially dangerous to developing fetuses, but as the recent mercury-poisoning case of actor Jeremy Piven shows (he apparently had a twice-daily sushi habit), adults must exercise caution as well - or at least moderation.
Essentially, Burger says that consumers should know "[t]he range of mercury in tuna is very great, so you're taking [a] risk if you don't know what kind of tuna you're eating." Some of her recommendations:
- You could lower your exposure to mercury by eating light tuna rather than white tuna, or albacore. In general, mercury levels in albacore are three times higher than those found in light tuna.
- Women who are considering becoming pregnant should avoid fish with mercury levels greater than 0.5 ppm. This would mean not eating tuna sushi, since you can't consistently count on getting tuna that is on the lower end of the spectrum in terms of its mercury level.
- Adults who are not pregnant and are not of childbearing age shouldn't eat more than seven or eight pieces of tuna sushi per month.
-Some fish such as salmon are generally lower in mercury, and are safer to consumer in larger quantities.
More on Sushi
DNA Tests Uncover Sushi Fraud At Restaurants
Japan Will Ignore Ban on Bluefin Tuna, Says The Fish Isn't That Endangered
Nobu Still Serves Endangered Bluefin Tuna, Places Moronic Warning Labels on Menus
Save a Species: Stop Eating Bluefin Tuna (At Least for Awhile)
The Carbon Footprint of Sushi
Freshwater Fish Laced with Mercury (Video News)