Mercury in U.S. Commercial Finfish and a Fish Size-Mercury Concentration Correlation for Swordfish

Introduction: Mercury, a byproduct of industrial waste and combustion processes, is biotransformed to methylmercury (MeHg) by aquatic microbes and bioaccumulates in fish.  Fetuses and infants are especially sensitive to the neurotoxic effects of MeHg, as excessive exposure can impede the development of language, attention, memory, motor skills and learning ability.  Because fetal and infant intake is dependent upon the maternal diet, pregnant and nursing women should exercise caution when consuming fish, as some species contain high MeHg concentrations.

Purpose: The purposes of this study were 1) to examine the mercury content in many commercial finfish species commonly consumed in the U.S. and 2) to develop a fish size-mercury concentration correlation for swordfish.

Methods: Commercial seafood vendors from six regions of the U.S. (Great Lakes, Mid-Atlantic, New England, Northwest, Southeast, and Southwest) provided 77 species of fish (300 composites of three fish).  Total mercury content was determined using a thermal decomposition (gold) amalgamation atomic absorption spectrophotometer (TDA/AAS) mercury analyzer (DMA-80), which thermally decomposes samples, captures mercury via gold amalgamation and measures total mercury content via AAS.

Results: Fish muscle tissue contained mercury concentrations ranging from 1 – 1425 ppb.  The most popularly consumed species, including salmon (13–62 ppb), Alaskan Pollock (11 ppb), tilapia (16 pp), channel catfish (1 ppb), Atlantic cod (82 ppb) and pangasius/swai (2 ppb), were low in mercury, while king mackerel (1425 ppb) and swordfish (1107 ppb) were above the current FDA Action Limit of 1000 ppb.  Swordfish was further investigated and it was determined that dressed carcasses above 230 lbs. exceeded the FDA limit.

Significance: The results of this study will help sensitive populations make safe and informed decisions regarding seafood consumption.  This survey will also help regulatory agencies as they prevent fish with excessive mercury from entering the marketplace.