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

MERCURY 154
2.2.2.8 Cancer
2. HEALTH EFFECTS
Inorganic Mercury. No studies were located regarding cancer in humans after oral exposure to inorganic
mercury.
Results of a 2-year National Toxicology Project (NTP 1993) study indicated that mercuric chloride may
induce tumors in rats. Fischer 344 rats (60 per sex per group) received 0, 1.9, or 3.7 mg Hg/kg/day as
mercuric chloride by gavage for 2 years. There were increases in the incidence of forestomach squamous
cell papillomas and an increase in the incidence of thyroid follicular cell carcinomas in males in the
3.7 mg/kg group (NTP 1993). In B6C3F1 mice exposed to 0, 3.7, or 7.4 mg Hg/kg/day as mercuric
chloride, renal tubule tumors were evident in 3 of the 49 high-dose males (NTP 1993), but the incidence of
these tumors was not significantly increased. There was no evidence of carcinogenicity in the exposed
female mice. The cancer effect level (CEL) from this study is recorded in Table 2-2 and is plotted in Figure
2-2.
Organic Mercury. No studies were located regarding cancer in humans following oral exposure to organic
mercury.
Significant increases in renal tumors have been observed in rodents exposed either to methylmercuric
chloride or phenylmercuric acetate. Dietary exposure of both ICR and B6C3F 1 mice for 2 years has
resulted in significant increases in renal epithelial cell tumors (Hirano et al. 1986; Mitsumori et al. 1981,
1990). At the highest dose of 0.69 mg Hg/kg/day (dose levels 0, 0.03, 0.14, 0.69), only male B6C3F 1 mice
(n=60M,60F) showed significant increases in the incidence of renal epithelial cell adenomas and
carcinomas (Mitsumori et al. 1990). No tumors were observed in the females B6C3F 1 mice exposed to up
to 0.6 mg Hg/kg/day. The high dose in males and females also resulted in chronic nephropathy and
regeneration of the proximal tubules (more severe in males). At 0.73 mg Hg/kg/day, male ICR mice
showed significant increases in the incidence of epithelial cell adenocarcinomas (Hirano et al. 1986).
Similar effects were observed in the ICR male mice at the highest dose of 1.6 mg Hg/kg/day (Mitsumori et
al. 1981). No increase in tumor incidence was observed in rats exposed via the diet for 2 years to methylmercuric
chloride at doses as high as 0.1 mg Hg/kg/day (Verschuuren et al. 1976).
Exposure of male Wistar rats to phenylmercuric acetate in the drinking water at 4.2 mg Hg/kg/day for
2 years resulted in a significant increase in renal cell adenomas (Solecki et al. 1991). However, this report