Update: January 1995
Current Massachusetts Regulatory Limit
MMCL = 0.005 mg/L. ORS has adopted the MCL published by the U.S. EPA as part of the Phase V rule (57 FR 31776; 7-17-92).
Federal Regulatory Limit
The MCL of 0.005 mg/L is based on the PQL for dichloromethane. The MCLG is set to zero based on the evidence for carcinogenic potential.
Basis for Criteria
An MCLG of zero is assigned for dichloromethane based on carcinogenic effects. The MCL is based on the dichloromethane PQL.
Liver Toxicity. In a two-year study conducted in rats, treatment-related histological alterations of the liver were evident at doses of 50 mg/kg/day or higher. A NOAEL of 5.85 mg/kg/day was identified from this study (NCA, 1982).
The cancer classification is based on inadequate human data and sufficient evidence of carcinogenicity in animals; increased incidence of hepatocellular neoplasms and alveolar/bronchiolar neoplasms in male and female mice, and increased incidence of benign mammary tumors in both sexes of rats; salivary gland sarcomas in male rats and leukemia in female rats were reported (NCA, 1982, 1983). This classification is supported by some positive genotoxicity data, although results in mammalian systems are generally negative.
The MCL of 0.005 mg/L is associated with a maximum individual excess lifetime cancer risk* of 1 x 10-5 (57 FR 31776).
* This information on risk is extrapolated from information provided in the July 7, 1992 Federal Register that a 1 x 10-4 Excess Lifetime Cancer Risk (ELCR) is associated with a concentration of 0.05 mg/L.
PQL: 0.005 mg/L
U.S. EPA Methods 503.1 P/T
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 http://www.epa.gov/iris/. Please note that the information in IRIS may differ from that used in the derivation process as published in the Federal Register notice.
NCA (National Coffee Association). 1982. 24 month chronic toxicity and oncogenicity study of methylene chloride in rats. Final Report. Prepared by Hazelton books of America, Inc. Vienna,VA. Unpublished.
NCA (National Coffee Association) 1983. Twenty four month oncogenicity study of methylene chloride in mice. Final Report. Prepared by Hazelton Literature of America. Inc. Vienna, VA.
Federal Register. July 17, 1992. Part III. Environmental Protection Agency. 40 CFR Parts 141 and 142. National Primary Drinking Water Regulations; Synthetic organic Chemicals and Inorganic Chemicals; Final Rule. (57 FR 31776).