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

MERCURY 292
2. HEALTH EFFECTS
Cancer. Mercury has not been determined to be carcinogenic in humans (Cragle et al. 1984; Kazantzis
1981). An excess of lung cancer (type not specified) was found in Swedish chloralkali workers, but these
workers had also been exposed to asbestos (Barregard et al. 1990). A significant association between the
farm use of mercury-containing fungicides and lymphocytic leukemia in cattle was presented by Janicki et
al. (1987). However, this study is limited because exposure to other chemicals was not adequately addressed
and risk estimates were not adjusted for other risk factors for leukemia.
Animal data, however, suggest that mercuric chloride, and methylmercuric chloride, phenylmercuric acetate
are tumorigenic in rats and/or mice. In a 2-year NTP (1993) study, male Fischer 344 rats administered
mercuric chloride by gavage had an increased incidence of squamous cell papillomas of the forestomach and
an increased incidence of thyroid follicular cell carcinomas at 3.7 mg Hg/kg/day. There is equivocal
evidence of carcinogenicity in female rats (a nonsignificant incidence of squamous cell papillomas) and in
male B6C3F1 mice (a nonsignificant incidence of renal tubule adenomas and carcinomas). Dietary exposure
of ICR and B6C3F1 mice to methylmercuric chloride resulted in significant increases in the incidences of
renal epithelial cell adenomas and/or carcinomas in males at doses as low as 0.69–0.73 mg Hg/kg/day
(Hirano et al. 1986; Mitsumori et al. 1981, 1990). Similar increases were not observed in females. Renal
cell adenomas were also significantly increased in male Wistar rats that received 4.2 mg Hg/kg/day as
phenylmercuric acetate in their drinking water (Solecki et al. 1991). This study is limited, however, because
an insufficient number of animals were tested to adequately assess carcinogenicity.
Swiss mice were exposed for 15 weeks to drinking water containing methylmercuric chloride at
concentrations of 0.038, 0.095, and 0.38 mg Hg/kg/day (Blakley 1984). Urethane (1.5 mg/g) was
subsequently given intraperitoneally to the mice at week 3 of the study. Methylmercury exposures of
0.038 and 0.095 mg Hg/kg/day produced a significant increase in the incidence of urethane-induced
pulmonary adenomas. The author suggested that methylmercury enhances the formation of pulmonary
adenomas and that the immunosuppressive activity of methylmercury may be partially responsible for this
tumor-enhancing effect. No other studies were located regarding carcinogenic effects in animals following
oral exposure to mercury.
The Department of Health and Human Services (DHHS), and the International Agency for Research on
Cancer (IARC) have not classified mercury as to its human carcinogenicity. The Environmental Protection
Agency has determined that mercury chloride and methylmercury are possible human carcinogens.