Chlorobenzene

Endpoint summary

Additional information

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 in different studies. In an in vitro chromosome aberration test in Chinese Hamster Ovary cells no clastogenic activity was observed in the absence of metabolic activaton at concentrations ranging from 30 to 300 µg/ml, with severe cytotoxicity at higher concentrations. In the same study no consistent or dose dependent effect was observed in two tests in the presence of S9 at concentrations ranging from 50 to 510 µg/ml (Loveday 1989). The same authors conducted a SCE-assay in Chinese Hamster Ovary cells and reported that chlorobenzene induced SCEs in two experiments without metabolic activation, but only at toxic doses (300 – 1000 µg/ml), 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 (300 µg/ml) (Loveday 1989). The authors of this study mention that chlorobenzen was previously tested in another study and reported to be not clastogenic. “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). 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.” (Loveday 1989). In one in vivo publication with limited documentation chlorobenzene was tested in a dominant lethal test, a SCE and a MNT in mice were dosed orally with 3.2 – 400 mg/kg. All tests were reported to be negative (Fel’dt 1985, reviewed in German Commission for the Investigation of Health Hazards of chemical compounds in the Work Area. Chlorobenzol. 1995). 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. SCOEL evaluated chlorobenzene and concluded: “ Weighting the total body of data obtained in genotoxicity and carcinogenicity studies of chlorobenzene (one positive in vitro gene mutation test and several negative in vitro genotoxicity assays, and one negative long-term mouse ans one negative long-term rat carcinogenicity study), the committee concludes that occupational exposure to monochlorebenzene under normal conditions is of no health concern with respect to potential genotoxic or carceinogenic effects” (SCOEL/SUM/42. 2003) The overall evaluation of the available data indicate that chlorobenzene has no consistent genotoxic potential.

Short description of key information:
Weighting the total body of data obtained in genotoxicity and carcinogenicity studies chlorobenzene is of no health concern with respect to potential genotoxic or carceinogenic effects.

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 .