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

MERCURY 418
5. POTENTIAL FOR HUMAN EXPOSURE
Fish and Shellfish. As part of the National Pesticide Monitoring Program (NPMP), the U.S. Fish and
Wildlife Service collected freshwater fish during 1976–1977 from 98 monitoring stations nationwide and
analyzed them for mercury and other heavy metals (May and McKinney 1981). As part of this program,
duplicate composite samples of a bottom-dwelling species and several representative predatory species
were collected. Bottom-dwelling species sampled included common carp, common sucker, and channel
catfish or other catfish species. Predatory species sampled were rainbow, brown, brook or lake trout at
cold water stations; largemouth bass or other sunfish family members, such as crappie or bluegill, at warm
water stations; and walleye or other perch family members at cool water stations. May and McKinney
(1981) reported that the mean concentration of mercury was 0.153 ppm (wet weight basis) in the 1972
NPMP survey and that the mean concentration declined significantly to 0.112 ppm (range, 0.01–0.84 ppm)
in the 1976–1977 survey. This decline was presumably due to curtailed production, use, and emissions of
mercury (Lowe et al. 1985). May and McKinney (1981) identified an arbitrary 85th percentile
concentration of 0.19 ppm for mercury to identify monitoring stations having fish with higher than normal
concentrations of mercury. Most of these stations were downstream of industrial sites (e.g., chloralkali
operations, pulp and paper plants; or pre-1900 gold and silver mining operations), while others were
located in areas with major mercury ore (cinnabar) deposits. In a follow-up NPMP study conducted from
1980–1981, Lowe et al. (1985) reported a geometric mean mercury concentration of 0.11 ppm (wet
weight) (range, 0.01–1.10 ppm). These authors reported that the downward trend in mercury residues in
fish reported by May and McKinney (1981) may have leveled off, since no significant difference in the
geometric mean values was detected in the follow-up study conducted in 1984–1985 as part of the
National Contaminant Biomonitoring Program (Lowe et al. 1985; Schmitt and Brumbaugh 1990).
However, large variations in mercury uptake among the fish species sampled, as well as among size classes
of fish within the same species, may mask actual trends.
From 1986 to 1989, the National Study of Chemical Residues in Fish (NSCRF) was conducted by the EPA
to assess the concentrations of 60 toxic pollutants (including mercury) in the tissues of benthic and
predatory gamefish nationwide (EPA 1992f). Benthic species were analyzed as whole-body samples,
while game fish species were analyzed as fillet samples, and all concentrations were reported on a wet
weight basis. Mercury was detected at 92% of the 374 sites surveyed nationwide at a mean concentration
of 260 ng/g (0.26 ppm) (median concentration of 0.17 ppm and a maximum concentration of 1.8 ppm), and
at 2% of the sites, measured mercury concentrations exceeded 1 ppm. Most of the higher mercury
concentrations in fish were collected in the Northeast. Ten of the sites in the top 10th percentile for high
mercury concentrations were near pulp and paper mills, four were near Superfund sites, and most of the