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The bacterial mutagenicity of chlorobenzene was examined in two tests at concentrations from 0.02-1.28 µl/plate and 3.3-3333.3 µg/plate. Both tests were conducted according to OECD Guideline 471 in the presence and absence of metabolic activation. The results revealed that chlorobenzene can be considered as non-mutagenic in the Ames test (Shimizu1983, Haworth 1983).

Chlorobenzene was tested for its mutagenic potential also in the L5178Y tk+/-mouse lymphoma cell forward mutation assay according to OECD guideline 476 (In vitro Mammalian Cell Gene Mutation Test) with deviations (Analytical purity was not reported. No colony size was reported, McGregor 1988.). Cultures were exposed to 5 chlorobenzene concentrations (between 6.25 - 200 ug/ml) for 4 hours, then cultured for 2 days before plating in soft agar with or without 3 µg/ml of trifluorothymidine (TFT). Chlorobenzene was tested at least twice. The experiments were conducted in presence and absence of metabolic activation (S9 mix).Out of four experiments without S9 mix, statistically significant increases in mutant fractions were observed in three experiment, whereas in one of these three experiments the relative total growth was less than 1% so it was considered inconclusive. The two experiments in the presence of S9 mix gave a significant and consistent responses..According to the author it was possible to conclude that chorobenzene was mutagenic in mammalian cells.

However, there are two further Mouse lymphoma tests available which are cited in a comprehensive review by BUA in 1990 and a comprehensive data evaluation by ECB in 2000 which yielded negative results in the presence and in the absence of a metabolic activation system using concentrations ranging 0.0001 - 0.1 µl/ml (corresponding to 0.1 to 110 µg/ml, BUA 1990) or .using concentrations ranging from 0.0005 to1 µl/ml (corresponding to 5.5 - 1100 µg/ml , ECB 2000)

Mutagenicity was additionally tested in vivo by a Sex Linked Recessive Lethal (SLRL) test in Drosophila melanogaster in three application routes: inhalation and adult feeding and ip. injection . There is no indication of any mutagenic effect in any germ cell stage (Valencia 1982, BUA1990, Foureman 1994).

The clastogenic potential of chlorobenzene was analysed by a chromosome aberration test and a SCE-assay in Chinese Hamster Ovary cells ( Loveday 1989). An increase in chromosomal aberrations (AB) was seen at one intermediate dose in the first trial with metabolic activation. This was not reproducible. No ABs were induced in the absence of metabolic activation up to 500 µg/mL, that allowed only 8 metaphase cells to be analysed. Chlorobenzene induced SCEs in two experiments without metabolic activation, but only at toxic doses, where cell confluency was reduced to approximately 10% of control values. No increase in SCEs was seen with metabolic activation up to a dose that reduced the confluency of the cells to about 80% of control. However, Loveday (1989) discussed that Chlorobenzene was previously reported as negative for induction of SCEs and ABs in CHO cells as part of a US EPA project (Loveday, unpublished reports, cited in Loveday 1989). In the EPA sponsored study, lower concentrations were tested based on the solubility limit of 500 µg/mL, and more conservative data analysis procedures were employed. Based on these results chlorobenzene was considered to be non-clastogenic in.vitro. Furthermore, the DNA damaging potential of chlorobenzene was examined in vivo by a comet assay in C57BL mice (Vaghef 1995). Peripheral lymphocytes and bone marrow cells were examined following both a single and repeated i..p. injections of 750 mg/kg bw. There was only a weak evidence of chlorobenzene-induced DNA damage after the repeated high exposure in peripheral lymphocytes, but no indication of such effect in bone marrow cells. In summary, :most of the mutation assays carried out with chlorobenzene have not provided any evidence for mutagenicity of the compound. There is some evidence that chlorobenzene may bind to DNA. The overall evaluation of the available data indicates that chlorobenzene is not genotoxic.

Short description of key information:
Chlorobenzene showed no mutagenic activity in the Ames test, the availble tests for point mutations in mammalian cells are not consistent. Chlorobenzene does not induce chromosome aberrations but there is some evidence that DNA damage may occur at high doses. Overall chlorobenzene is regarded to be non-mutagenic

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Up to now Chlorobenzene is not classified into one of the categories for mutagenicity.

Based on the available data and the consideration above and taking into account EC Regulation (GHS/CLP) chlorobenzene has not to be classified/labelled .