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CASRN: 7439976

Update: May 2004

Current Massachusetts Regulatory Limit
MMCL = 0.002 mg/L. ORS has adopted the MCL promulgated by the U.S. EPA.

Federal Regulatory Limit
The MCL for mercury is equal to the MCLG of 0.002 mg/L.

Basis for Criteria

The MCLG is calculated based on the oral RfD for mercuric chloride, an inorganic form of mercury (presented below) and assuming that a 70 kg adult ingests 2 L/day of drinking water. A relative source contribution factor of 20% is incorporated into the final value.

RfD: 0.0003 mg/k/day (U.S. EPA, 1995a)
UF: 1000 (10 = LOAEL to NOAEL; 10 = subchronic to chronic; 10 = inter- and intra-species conversion
MF: 1

Critical Effects
In 1987, U.S. EPA convened a panel of mercury experts who met at a Peer Review Workshop on Mercury Issues. A number of recommendations came out of this meeting. The most sensitive adverse effect for mercury risk assessment was identified as formation of mercuric-mercury-induced autoimmune glomerulonephritis. The Brown Norway rat was identified as a good surrogate for the study of mercury-induced kidney damage in sensitive humans. Information from three studies (Druet et al., 1978, Andres, P., 1984, Bernaudin et al., 1981) using the Brown Norway rat was selected as the basis for the panel's recommendation of 0.010 mg/L as the DWEL for inorganic mercury. However, the recommended DWEL of 0.010 mg/L was derived as the product of an intensive review and workshop discussions of the entire inorganic mercury database. The oral RfD of 0.0003 mg/kg/day was back calculated from the DWEL (U.S. EPA, 1995a).

Cancer Assessment: 
C (by the old U.S. EPA classification system). Under the new, proposed guidelines (U.S. EPA, 1999), this classification would correspond to the descriptor "suggestive evidence of carcinogenicity but not sufficient to assess human carcinogenic potential".

There are no human data and only limited evidence of carcinogenicity in rats and mice. In a 1993 NTP study in which male rats were gavaged for two years with mercuric chloride, observed cancer included focal papillary hyperplasia and squamous cell papillomas in the forestomach, as well as thyroid follicular cell adenomas and carcinomas. However, NTP questioned the relevance of these tumors to humans based on the fact that there is no evidence that the forestomach papillomas progress to malignancy and the thyroid tumors are secondary to hyperplasia. The authors reported that the doses exceeded the Maximum Tolerated Dose (MTD) for male rats. Two other studies had equivocal results (NTP, 1993). A second study indicated equivocal evidence in male mice of renal tubular adenomas and adenocarcinomas, which is a rare tumor type in mice. However, the increased incidence of this tumor was statistically significant compared to historic controls. A similar increasing trend for renal tubular cell tumors was observed in several mouse studies involving chronic dietary exposure to methylmercury chloride (Hirano et al., 1986; Mitsumori et al., 1981, 1990). In these studies, increases in renal tubular tumors were seen at doses at which substantial nephrotoxicity was observed. Mercuric chloride produced mixed results in a series of genotoxicity tests (U.S. EPA, 1995b).

Heavy metal

Analytical Information
: 0.0005 mg/l

Analytical Methods
200.7; ICP/AA
245.1; manual cold vapor

PQLs and analytical methods may have been updated since this guidance value was last revised. Updated analytical methods for drinking water and their associated PQLs may be found at US EPA Drinking Water Analytical Methods

Other Regulatory Data
Any Health Advisories, Reference Doses (RfDs), cancer assessments or Cancer Potency Factors (CPFs) referenced in this document pertain to the derivation of the current guidance value. Updated information may be obtained from the following sources:

Health Advisories - The U.S. EPA provides guidance for shorter-term exposures for chemicals based on their non-cancer effects. Current health advisories may be more current than those used to derive MCLs and may be found at US EPA Current Drinking Water Health Advisories

RfDs, cancer assessments and CPFs - For specific information pertaining to derivation of drinking water criteria, consult the Federal Register notice that announces the availability of the most current guidance for that chemical. In addition, information on other current RfDs and CPFs as well as cancer assessments for specific chemicals may be found in the U.S. EPA Integrated Risk Information System (IRIS) at Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.

Andres, P. 1984. IgA-IgG disease in the intestine of Brown Norway rats ingesting mercuric chloride. Clin. Immunol. Immunopathol. 30: 488-494.

Bernaudin, J.F., Druet, E., Druet, P. and Masse, R.. 1981. Inhalation or ingestion of organic or inorganic mercurials produces auto-immune disease in rats. Clin. Immunol. Immunopathol. 20: 129-135.

Druet, P., Druet E., Potdevin, F. and Sapin, C. 1978. Immune type glomerulonephritis induced by HgCl2 in the Brown Norway rat. Ann. Immunol. 129C: 777-792.

Hirano, M., K. Mitsumori, K. Maita and Y. Shiraso. 1986. Further carcinogenicity study on methylmercury chloride in ICR mice. Jap. J. Vet. Sci. 48(1): 127-135.

Mitsumori, K., Maita, K., Saito, T. Tsuda, S. and Shirasu, Y. 1981. Carcinogenicity of methylmercury chloride in ICR mice: Preliminary note on renal carcinogenesis. Cancer Lett. 12: 305-310.

Mitsumori, K., Hirano, M., Ueda, H., Maita, K. and Shirasu, Y. 1990. Chronic toxicity and carcinogenicity of methylmercury chloride in B6C3F1 mice. Fund. Appl. Toxicol. 14: 179-190.

NTP (National Toxicology Program). 1993. Toxicology and carcinogenesis studies of mercuric chloride (CAS No. 7487-94-7) in F344 rats and B3C3F1 mice (gavage studies).

NTP Technical Report Series No. 408. National Toxicology Program, U.S. Department of Health and Human Services, Public Health Service, National Institutes of Health, Research Triangle Park, NC.

U.S. EPA (U.S. Environmental Protection Agency). May 1, 1995a. Integrated Risk Information System (IRIS). Sec I.A. - Reference dose for chronic oral exposure. U.S. Environmental Protection Agency. Washington, D.C.

U.S. EPA (U.S. Environmental Protection Agency). June 1, 1995b. Integrated Risk Information System (IRIS). Sec II.A. - Evidence for human carcinogenicity. U.S. Environmental Protection Agency. Washington, D.C.

U. S. EPA (U.S. Environmental Protection Agency). July 1999. Guidelines for Carcinogen Risk Assessment. Review Draft. NCEA-F-0644. Risk Assessment Forum.