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Key value for chemical safety assessment

Additional information

There is almost no indication for an interaction of chloroform or its metabolites formed in vivo with DNA in liver or kidney, which is supported by the lack of evidence in vivo for the induction of DNA strand breaks or repair and the absence of gene mutation induction in the mouse liver. A newly performed mammalian erythrocytes micronucleus test with Sprague Dawley rats receiving for five consecutive days doses of 120, 240 or 480 mg/kg via oral gavage concluded that chloroform did not induce micronuclei in the polychromatic erythrocytes of the bone marrow of female and male Sprague-Dawley rats (Whitwell 2009). The analysis of the ratio of polychromatic to normochromatic erythrocytes and the frequency of micronucleated polychromatic erythrocytes (MN PCE) in the negative vehicle control of the study were considered as valid. The clastogen positive control group exhibited statistically significantly increased numbers of MN PCE. Also the aneugenic positive control group produced significant upward shift in distribution of MN PCE. The test system therefore was considered as valid. Thus, this new study on the mutagenicity of chloroform gives evidence for the non-genotoxicity of chloroform. The formerly available information on clastogenic effects, which was used in the European Union risk assessment on chloroform, provided a less clear picture than the new mammalian erythrocytes micronucleus study. One study in Long Evans rats receiving chloroform via oral gavage or as intraperitoneal injection (Fujie et al. 1990) gave clear evidence for chromosomal aberrations in the bone marrow of rats. Another study provided mixed evidence by finding a significant increase in micronuclei but no chromosal aberrations in mouse bone marrow (Shelby and Witt 1995). All other studies provided uncertain evidence or no evidence for a mutagenic effect of chloroform. However, the available data were not consistent in the responses with regard to the type of observation (micronucleus or chromosomal aberrations), species (rat or mouse) or target (most studies investigated bone marrow). The only clear positive study (Fujie et al. 1990) suggested that intraperitoneal administration caused greater sensitivity than oral administration (with bone marrow as the target), but significant responses were obtained with either route. Moreover, the effects observed in this study at a dose level almost 1000-fold lower than in a micronucleus study in mouse bone marrow and the lack of consistency of the likely tissue concentrations of chloroform in this study with the no-observed effects at much higher chloroform concentrations in a series of in vitro chromosomal aberration studies are not easily explained.

Short description of key information:
The majority of in vitro and in vivo assays on the mutagenicity of chloroform produced negative results or only slightly positive results. In order to clarify the uncertainties, a new mammalian erythrocyte micronucleus test was performed in Sprague-Dawley rats according to the current OECD and GLP guidelines (Whitwell 2009). This new in vivo assay did not find any genotoxic effect produced by chloroform exposure.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on the negative results found in the newly performed mammalian erythrocytes micronucleus test (Whitwell 2009) no classification of chloroform for mutagenicity is suggested.