COS 108-4 - The Geography of Toxins: Mercury and PCBs in the daily catch

Thursday, August 11, 2011: 2:30 PM
6A, Austin Convention Center
Amy Freitag1, Mark Hooper2 and Daniel Rittschof1, (1)Marine Science and Conservation, Duke University, Beaufort, NC, (2)Hooper Seafood

Mercury and PCB’s are persistent chemicals commonly used to indicate levels of toxins in seafood that warrant health concern. More specifically, they inform the toxicity level indicated by a little red flag on the “sustainable seafood cards” marketed by the Monterey Bay Aquarium. However, studies to date have been conducted on a national level and fishers in Down East, NC questioned if and how these results apply to their seafood. In collaboration between these fishers and a graduate student, mercury and PCB levels were measured in 8 seafood types (hard and soft blue crab, pink and brown shrimp, oysters, clams, mullet, and spot) marketed as “local seafood” in local restaurants and the community supported fishery. Samples were taken across the state inshore waters, including Albemarle, Pamlico, Croatan, Core, and Bogue Sounds.


Levels of mercury and PCB’s were overall low (.02-.2 mg/kg mercury dry weight), as expected for small, short-lived species. Shrimp (average .03 mg/kg mercury) were the least contaminated and blue crabs (average .21 mg/kg mercury) were the most. However, the levels varied as much by location as they did by species, suggesting that levels of contamination should be assessed at a much smaller scale than is currently being used. Particular streams identified by fishers as “bad water”, or polluted by upstream practices, tended to be higher in contaminants as well, suggesting that fisher knowledge based on observations of ecological changes might be a good proxy for contamination levels. Overall, this study supports the adage “know your fisher”, or the practice to ask where exactly your fish comes from before purchasing.

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Banner photo by Flickr user greg westfall.