Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Seafood substitutions can expose consumers to unexpectedly high mercury


New measurements from fish purchased at retail seafood counters in 10 different states show the extent to which mislabeling can expose consumers to unexpectedly high levels of mercury, a harmful pollutant.

Fishery stock "substitutions"—which falsely present a fish of the same species, but from a different geographic origin—are the most dangerous mislabeling offense, according to new research by University of Hawai‘i at Mānoa scientists.

Fish market in Oahu's Chinatown. Photo courtesy Flickr user Michelle Lee.

“Accurate labeling of seafood is essential to allow consumers to choose sustainable fisheries,” said UH Mānoa biologist Peter B. Marko, lead author of the new study published in the scientific journal PLOS One. “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.”

The study included two kinds of fish: those labeled as Marine Stewardship Council- (MSC-) certified Chilean sea bass, and those labeled simply as Chilean sea bass (uncertified). The MSC-certified version is supposed to be sourced from the Southern Ocean waters of South Georgia, near Antarctica, far away from man-made sources of pollution.  MSC-certified fish is often favored by consumers seeking sustainably harvested seafood but is also potentially attractive given its consistently low levels of mercury.

In a previous study, the scientists had determined that fully 20 percent of fish purchased as Chilean sea bass were not genetically identifiable as such. Further, of those Chilean sea bass positively identified using DNA techniques, 15 percent had genetic markers that indicated that they were not sourced from the South Georgia fishery.

In the new study, the scientists used the same fish samples to collect detailed mercury measurements.  When they compared the mercury in verified, MSC-certified sea bass with the mercury levels of verified, non-certified sea bass, they found no significant difference in the levels. That’s not the story you would have expected based on what is known about geographic patterns of mercury accumulation in Chilean sea bass.

“What’s happening is that the species are being substituted,” Marko explained. “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.”

But there’s another confounding factor. Even within the verified, MSC-certified Chilean sea bass samples, certain fish had very high mercury levels—up to 2 or 3 times higher than expected, and sometimes even greater than import limits to some countries.

Marko and his team again turned to genetics to learn more about these fishes’ true nature.  “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 bottom line:  Most consumers already know that mercury levels vary between species, and many public outreach campaigns have helped educate the public about which fish species to minimize or avoid.  Less appreciated is the fact that mercury varies considerably within a species.

“Because mercury accumulation varies within a species’ geographic range, according to a variety of environmental factors, the location where the fish is harvested matters a great deal,” Marko said.

“Although on average MSC-certified fish is a healthier option than uncertified fish, with respect to mercury contamination, our study shows that fishery-stock substitutions can result in a larger proportional increase in mercury,” Marko said. “We recommend that consumer advocates take a closer look at the variation in mercury contamination depending on the geographic source of the fishery stock when they consider future seafood consumption guidelines.”


Marko PB, Nance HA, van den Hurk P (2014) Seafood Substitutions Obscure Patterns of Mercury Contamination in Patagonian Toothfish (Dissostichus eleginoides) or “Chilean Sea Bass”. PLoS ONE 9(8): e104140. doi: 10.1371/journal.pone.0104140

University of Hawaiʻi at Mānoa

Peter Marko, (808) 956-6146
Associate Professor, Biology
Talia Ogliore, (808) 956-4531
Public Information Officer, Vice Chancellor for Research

Talia S Ogliore | Eurek Alert!
Further information:

Further reports about: DNA contamination exposure fishery seafood species techniques

More articles from Health and Medicine:

nachricht Antioxidants cause malignant melanoma to metastasize faster
09.10.2015 | University of Gothenburg

nachricht Finding cannabinoids in hair does not prove cannabis consumption
07.10.2015 | Universitätsklinikum Freiburg

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Reliable in-line inspections of high-strength automotive body parts within seconds

Nondestructive material testing (NDT) is a fast and effective way to analyze the quality of a product during the manufacturing process. Because defective materials can lead to malfunctioning finished products, NDT is an essential quality assurance measure, especially in the manufacture of safety-critical components such as automotive B-pillars. NDT examines the quality without damaging the component or modifying the surface of the material. At this year's Blechexpo trade fair in Stuttgart, Fraunhofer IZFP will have an exhibit that demonstrates the nondestructive testing of high-strength automotive body parts using 3MA. The measurement results are available in a matter of seconds.

To minimize vehicle weight and fuel consumption while providing the highest level of crash safety, automotive bodies are reinforced with elements made from...

Im Focus: Kick-off for a new era of precision astronomy

The MICADO camera, a first light instrument for the European Extremely Large Telescope (E-ELT), has entered a new phase in the project: by agreeing to a Memorandum of Understanding, the partners in Germany, France, the Netherlands, Austria, and Italy, have all confirmed their participation. Following this milestone, the project's transition into its preliminary design phase was approved at a kick-off meeting held in Vienna. Two weeks earlier, on September 18, the consortium and the European Southern Observatory (ESO), which is building the telescope, have signed the corresponding collaboration agreement.

As the first dedicated camera for the E-ELT, MICADO will equip the giant telescope with a capability for diffraction-limited imaging at near-infrared...

Im Focus: Locusts at the wheel: University of Graz investigates collision detector inspired by insect eyes

Self-driving cars will be on our streets in the foreseeable future. In Graz, research is currently dedicated to an innovative driver assistance system that takes over control if there is a danger of collision. It was nature that inspired Dr Manfred Hartbauer from the Institute of Zoology at the University of Graz: in dangerous traffic situations, migratory locusts react around ten times faster than humans. Working together with an interdisciplinary team, Hartbauer is investigating an affordable collision detector that is equipped with artificial locust eyes and can recognise potential crashes in time, during both day and night.

Inspired by insects

Im Focus: Physicists shrink particle accelerator

Prototype demonstrates feasibility of building terahertz accelerators

An interdisciplinary team of researchers has built the first prototype of a miniature particle accelerator that uses terahertz radiation instead of radio...

Im Focus: Simple detection of magnetic skyrmions

New physical effect: researchers discover a change of electrical resistance in magnetic whirls

At present, tiny magnetic whirls – so called skyrmions – are discussed as promising candidates for bits in future robust and compact data storage devices. At...

All Focus news of the innovation-report >>>



Event News

EHFG 2015: Securing healthcare and sustainably strengthening healthcare systems

01.10.2015 | Event News

Conference in Brussels: Tracking and Tracing the Smallest Marine Life Forms

30.09.2015 | Event News

World Alzheimer`s Day – Professor Willnow: Clearer Insights into the Development of the Disease

17.09.2015 | Event News

Latest News

Unexpected information about Earth's climate history from Yellow River sediment

09.10.2015 | Earth Sciences

Single atom alloy platinum-copper catalysts cut costs, boost green technology

09.10.2015 | Life Sciences

Indefatigable Hearing

09.10.2015 | Life Sciences

More VideoLinks >>>