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

MERCURY 347
2. HEALTH EFFECTS
needed to evaluate the potential developmental toxicity of inorganic mercury to populations, specifically
young children, living near hazardous waste sites. Longitudinal studies for higher dose level acute and
intermediate exposures are needed to determine the potential delayed expression of toxicity.
Prenatal exposure to methylmercury from contaminated food during the early stages of pregnancy has
caused neurological damage in humans (Amin-Zaki et al. 1974; Bakir et al. 1973; Choi et al. 1978; Cox et
al. 1989; Engleson and Herner 1952; Harada 1978; Marsh et al. 1980, 1981, 1987; Matsumoto et al. 1965;
McKeown-Eyssen et al. 1983; Snyder and Seelinger 1976). Severe neurological impairment developed in
a child exposed in utero to methylmercury, and effects were still present at 6 years of age (Snyder and
Seelinger 1976). In animals, numerous oral exposure studies on the developmental effects of organic
mercury have been conducted. Disruptions in the development of the nervous system in rats, mice,
hamsters, and guinea pigs (Chang et al. 1977; Inouye and Kajiwara 1988; Khera and Tabacova 1973;
Reuhl et al. 1981a, 1981b) and in the immune system in rats (Ilback et al. 1991) have been reported.
Behavioral changes were also observed in rats and mice (Bornhausen et al. 1980; Hughes and Annau
1976; Olson and Boush 1975). Additional long-term inhalation, oral, and dermal studies for inorganic
and organic mercury are needed to evaluate the threshold of developmental effects in workers chronically
exposed to mercury or in populations living near hazardous waste sites.
Immunotoxicity. The results from two occupational studies indicate a decreased serum IgG levels in
workers to inhaled metallic mercury vapors (Bencko et al. 1990; Moszczynski et al. 1990b), but these studies
are limited and did not evaluate potential confounders (smoking and alcohol). Other studies in similarly
exposed populations did not observe an increases in serum immunoglobulins (IgA, IgG, IgE, or IgM) and
autoantibody titres (antilaminin or antiglomerular basement membrane antibodies) (Bernard et al. 1987;
Cardenas et al. 1993; Langworth et al. 1992b). There is limited information in humans that suggests that
certain individuals may develop an autoimmune response (Tubbs et al. 1982; Moszczynski et al. 1995).
Data on immunological effects following oral exposure to organic mercury compounds in humans are not
available. Oral exposures to inorganic and organic mercury in animals indicate that the immune system may
be a target organ for mercury. Immune deposits were observed in the intestines and kidneys of rats exposed
to mercuric chloride for 2 months, but no functional changes were evident in these tissues (Andres 1984).
Suppression of the lymphoproliferative response occurred at a higher dose of mercury in mice exposed to
mercuric chloride for 7 weeks (Dieter et al. 1983). Reduced natural killer cell activity in spleen and blood
was exhibited in mice administered a diet containing methylmercury for 12 weeks (Ilback 1991). It is
unknown how an adverse effect on the immune system from exposure to one form of mercury