Health Assessment Document for Dichloromethane (Methylene Chloride) Updated Carcinogenicity Assessment of Dichloromethane (Methylene Chloride): Addendum
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The addendum contains a review of the data from the latest National Toxicology Program (NTP) inhalation bioassay of dichloromethane (DCM) and an update of the inhalation cancer risk value. In addition, there is a recommendation for an estimate of unit risk for ingestion exposure, and an evaluation of metabolism and pharmacokinetic data for use in the development of cancer unit risk estimates. The recent NTP inhalation bioassay concluded that there was some evidence of carcinogenicity for male F344/N rats and clear evidence of carcinogenicity for female F344/N rats as shown by increased evidence of benign neoplasms of the mammary gland. There was clear evidence of carcinogenicity for male and female B6C3F1 mice as shown by increased incidence of alveolar/bronchiolar neoplasms and of hepatocellular neoplasms. There are data from two epidemiologic studies associated with exposure to DCM. Neither showed excessive risk to cancer, but each was considered to have sufficient limitations which prevent them from being judged negative studies. A review of the metabolism/pharmacokinetics concluded that possible approaches for interpreting the data are more illustrative than useful in risk estimation. Using EPA's Proposed Guidelines for Carcinogen Risk Assessment, there is a sufficient weight-of-evidence that DCM is a possible carcinogen in experimental animals, but for humans the data are inadequate. Therefore, DCM is classified, according to the Guidelines, as Category B2, i.e., a possible human carcinogen.