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

MERCURY 401
5. POTENTIAL FOR HUMAN EXPOSURE
0.001 mg/m 3 for the vapor concentrations, indicating that it was also nonleachable and did not readily
volatilize. This study also showed that concentrations of mercury in leachate could not be correlated with
the concentration of mercury in the soil or in the headspace vapors (Willett et al. 1992). Mercuric sulfide
has been found to strongly adsorb to soil, and even with weathering, any mercury released from the
mercuric sulfide is readsorbed by the soil (Harsh and Doner 1981).
The most common organic form of mercury, methylmercury, is soluble, mobile, and quickly enters the
aquatic food chain. This form of mercury is accumulated to a greater extent in biological tissue than are
inorganic forms of mercury (Riisgard and Hansen 1990). Methylmercury in surface waters is rapidly
accumulated by aquatic organisms; concentrations in carnivorous fish (e.g., pike, shark, and swordfish) at
the top of both freshwater and marine food chains are biomagnified on the order of 10,000–100,000 times
the concentrations found in ambient waters (Callahan et al. 1979; EPA 1984b; WHO 1990, 1991). The
range in experimentally determined bioconcentration factor (BCF) values is shown in Table 5-6. The
bioaccumulation potential for methylmercury in fish is influenced by the pH of the water, with a greater
bioaccumulation seen in waters with lower pH (Ponce and Bloom 1991). Mercury concentrations in fish
have also been negatively correlated with other water quality factors, such as alkalinity and dissolved
oxygen content (Wren 1992).
The biomagnification of methylmercury has been demonstrated by the elevated levels found in piscivorous
fish compared with fish at lower levels of the food chain (Jackson 1991; Kohler et al. 1990; Porcella 1994;
Watras and Bloom 1992). Biomagnification factors for methylmercury in the food webs of Lake Ontario
were lowest for the transfer of methylmercury from mysids to amphipods (1.1), plankton to amphipods
(1.8), and plankton to mysids (2.4); were intermediate for the transfer from mysids to fish (5.1) and
amphipods to fish (6.5); and were highest for the transfer from plankton to fish (10.4) (Evans et al. 1991).
(The biomagnification of methylmercury from water through several trophic levels is compared to the
biomagnification of inorganic mercury in Table 5-7.) Watras and Bloom (1992) reported that
biomagnification of methylmercury in Little Rock Lake seems to be a result of two processes: the higher
affinity of inorganic mercury in lower trophic level organisms and the high affinity of methylmercury in
fish. Fish appear to accumulate methylmercury from both food sources and the water column. However,
Hall et al. (1997) found that food was the predominant source of mercury uptake in fish. The biological
concentration factor (BCF) of methylmercury in fish in Little Rock Lake was three million (Porcella
1994). Mason et al. (1995) also compared bioaccumulation of inorganic mercury and methylmercury.
These authors showed that passive uptake of the mercury complexes (HgCl2 and CH3HgCl) results in high