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

MERCURY 471
5. POTENTIAL FOR HUMAN EXPOSURE
28 ppm (wet weight), in liver tissue (Becker et al. 1995). Similarly, in Alaskan ringed seal, mean
methylmercury levels were 0.410 ppm (wet weight) and mean total mercury levels were 1.970 ppm (wet
weight) in liver tissue. However, no information was available for methylmercury levels in muscle tissue
from Alaskan mammals. An older report by Smith and Armstrong (1975) also examined total mercury and
methylmercury levels in marine mammal livers eaten by native Inuit in the Northwest Territory of Canada.
Smith and Armstrong (1975) reported total mercury concentrations of 143 and 26.2 ppm (wet weight) and
mean methylmercury levels of 0.300 and 0.120 ppm (wet weight) in liver tissue of bearded seals sampled in
1973 and 1974, respectively. Smith and Armstrong (1975) also reported total mercury concentrations of
27.5 ppm (wet weight) (maximum, 184 ppm), and 0.72 ppm in liver and muscle tissue, respectively, and
mean methylmercury levels of 0.96 and 0.83 ppm in liver and muscle tissue, respectively, of ringed seals
sampled near Victoria Island in Canada’s Northwest Territory. These authors also reported a mean total
mercury concentration of 143 ppm and a mean methylmercury concentration of 0.30 ppm in liver tissue of
bearded seals. The mean total mercury concentration in the muscle tissue of the bearded seals was 0.53 ppm
(no methylmercury concentrations in muscle tissue were available for this species).
In Greenland, the percentage of total mercury that was methylmercury in seal muscle tissue was 57–86%;
however, the concentration of total mercury was very low. Mercury concentrations in the blood of mothers
and infants in Greenland were closely correlated with the amount of marine mammal meat the mothers
consumed. Mercury concentrations in the blood of mothers eating primarily imported food ranged from 11.0
to 32.7 µg/L (ppb) and concentrations in the blood of their children ranged from 15.0 to 51.4 µg/L (ppb). In
contrast, mercury concentrations in the blood of mothers who consumed primarily a local diet heavy in
marine animals ranged from 16.4 to 44.6 µg/L (ppb) and concentrations in the blood of their children ranged
from 27.5 to 140.0 µg/L (ppb) (Hansen 1991).
Native American populations that depend heavily on marine mammals are considered to be at higher risk
than the general population. Wheatley and Paradis (1995a, 1995b) reported blood mercury levels in native
peoples from 514 communities across Canada. Of these individuals, 23% had methylmercury blood levels
>20 µg/L (the WHO assessment level), while 1.6% of these individuals had blood levels >100 µg/L (the
WHO benchmark for at-risk populations). Native American populations in the western Arctic (Alaska) may
be at similar risk as a result of their consumption of marine mammals, although no recent information on
methylmercury concentrations in blood, hair or urine for these populations was located. In Alaskan Inuit
women that consume marine mammal tissue, Galster (1976) reported higher total mercury levels in breast