revised final - Agency for Toxic Substances and Disease Registry ...

MERCURY 424
5. POTENTIAL FOR HUMAN EXPOSURE
possibly as a result of the increased bioavailability of organic mercury produced by aquatic microorganisms,
whereas inorganic mercury was the predominant form at the source (Parks et al. 1991).
Typical mercury concentrations in large carnivorous freshwater fish (e.g., pike) and large marine fish (e.g.,
swordfish, shark, and tuna) have been found to exceed 1 µg/g (ppm) (EPA 1984b; Fairey et al. 1997; FDA
1998; Hellou et al. 1992; Hueter et al. 1995), with mercury content again being positively correlated with
the age of the fish (Gutenmann et al. 1992; Hueter et al. 1995). Methylmercury concentrations in muscle
tissue of 9 species of sharks were analyzed from 4 locations off Florida (Hueter et al. 1995). Muscle tissue
methylmercury concentration averaged 0.88 µg/g (ppm) (wet weight) and ranged from 0.06 to 2.87 µg/g
(ppm), with 33.1% of the samples exceeding the FDA action level (1 ppm). A positive correlation
between methylmercury and shark body length (size) also was found, such that sharks larger than 200 cm
in total length contained methylmercury concentrations >1 ppm. Sharks collected off the southern and
southwestern coastal areas contained significantly higher concentrations than those caught in the northeast
coastal region (Cape Canaveral and north).
Methylmercury concentrations were highest in the Caribbean reef shark (Carcharhinus perezi). The two
most abundant shark species in the U.S. East Coast commercial shark fishery, sandbar (C. plumbeus) and
blacktip (C. limbatus) sharks, are of special concern with respect to human health. Although the mean
concentration of methylmercury in the sandbar shark (0.77 µg/g) was below the average for all sharks,
sandbar shark tissues contained up to 2.87 ppm methylmercury, and 20.9% of the samples exceeded the
FDA action level of 1 ppm. A total of 71.4% of the blacktip shark samples (mean, 1.3 µg/g) exceeded the
FDA action level. The authors suggest that continued monitoring of methylmercury concentrations in
various sharks species in the commercial marketplace is warranted. In a recent study of sportfish collected
in San Francisco Bay, Fairey et al. (1997) reported that the highest concentrations of mercury were
detected in leopard shark muscle tissue (1.26 ppm). Bluefin tuna caught in the Northwest Atlantic Ocean
in 1990 contained mercury at a mean muscle concentration of 3.41 µg/g (ppm) dry weight (Hellou et al.
1992).
As part of the National Oceanic and Atmospheric Administration (NOAA) Status and Trends Program
conducted from 1984 to 1987, mercury concentrations were analyzed in four marine bivalve species in
U.S. coastal waters (NOAA 1987). Mercury concentrations in bivalve tissues ranged from 0.01 to
0.48 µg/g (ppm) dry weight in oysters (Crassostrea virginica), 0.28 to 0.41 µg/g (ppm) in the Hawaiian
oyster (Ostrea sandwichensis), 0.05 to 0.47 µg/g (ppm) in the blue mussel (Mytilus edulis), and 0.04 to