Nature & Environment

Mislabeled Seafood May be Exposing Consumers to High Mercury Levels in Fish

Catherine Griffin
First Posted: Aug 20, 2014 09:39 AM EDT

Be careful what seafood you eat. It turns out that mislabeling may be exposing consumers to unexpectedly high levels of mercury in fish. Researchers have examined fish purchased at retail seafood counters in 10 different states and have discovered that mislabeling is a major issue.

"Accurate labeling of seafood is essential to allow consumers to choose sustainable fisheries," said Peter B. Marko, lead author of the new study, in a news release. "But consumers also rely on labels to protect themselves from unhealthy mercury exposure. Seafood mislabeling distorts the true abundance of fish in the sea, defrauds consumers, and can cause unwanted exposure to harmful pollutants such as mercury."

In this case, the researchers focused on Marine Stewardship Council (MSC)-certified Chilean sea bass and those labeled as simply Chilean sea bass. The MSC-certified version is supposed to be sourced from the Southern Ocean waters near Antarctica, far away from manmade sources of pollution. In addition, MSC-certified fish is often sought by consumers seeking to eat sustainably harvested seafood.

The scientists took samples of fish from seafood counters and then examined their levels of mercury. In this case, the researchers found that there was no significant difference in the levels of mercury in the two different types of sea bass.

"What's happening is that the species are being substituted," said Marko. "The ones that are substituted for MSC-certified Chilean sea bass tend to have very low mercury, whereas those substituted for uncertified fish tend to have very high mercury. These substitutions skew the pool of fish used for MSC comparison purposes, making certified and uncertified fish appear to be much more different than they actually are."

Even within the verified MSC-certified Chilean sea bass samples, the researchers found that certain fish had very high levels of mercury-up to two or three times higher than expected.

"It turns out that the fish with unexpectedly high mercury originated from some fishery other than the certified fishery in South Georgia," said Marko. "Most of these fish had mitochondrial DNA that indicated they were from Chile. Thus, fishery stock substitutions are also contributing to the pattern by making MSC-certified fish appear to have more mercury than they really should have."

The findings reveal that labeling may just be slipping when it comes to seafood. This shows not only the importance of accurate labeling, but also reveals that more stringent policies should be taken when it comes to checking fish that are put on the market.

The findings are published in the journal PLOS One.

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