I love sushi. It’s light but filling and my favorite treat when eating out. Unfortunately, sushi comes with a number of sustainability issues. After overfishing, mercury levels in sushi have been one of the biggest points of concern for sushi lovers—and one that’s getting looked at again in light of a new study finding that many species of tuna used in sushi contain high levels of mercury.
For the study, an environmental toxicology team at Rutgers University collected one hundred sushi samples from 54 restaurants and 15 supermarkets in New York, New Jersey and Colorado. They tested the tuna samples for mercury and found that they contained mercury at levels beyond the recommended benchmark, 0.1 micrograms of mercury per kilo of human bodyweight.
Certain species of tuna used in sushi have been found to contain mercury beyond the recommended level for ingestion. Photo By Barron Fujimoto/Courtesy Flickr
Bigeye tuna, or lean bluefin tuna, had the highest average level of mercury at 0.351 micrograms per kilo, followed closely by Bigeye tuna akami at 0.344 micrograms. On the opposite end of the scale, yellowfin tuna had an average of 0.164 micrograms per kilo, and bluefin toro contained 0.123 micrograms per kilo, lower than Bigeye tuna but still over the recommended level.
In addition to containing high levels of mercury, overfishing has made bluefin tuna a threatened species. For this reason, bluefin tuna is more expensive and therefore served most often in restaurants. Supermarkets tend to sell yellowfin tuna, which is cheaper, more plentiful and contains lower levels of mercury.
Mercury exposure can lead to neurological problems such as deafness, blindness and cerebral palsy. For a list of sushi fish containing the highest and lowest levels of mercury, check out the National Resources Defenses Council’s guide to mercury in sushi. Sushi restaurants often don’t mention which species of tuna they’re serving, so be sure to ask—and for the time being, steer clear of sushi that contains tuna.