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Key value for chemical safety assessment

Additional information

In vitro

There are no data available on the in vitro genotoxic potential of hydrocarbons, C6 -C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane. However, reliable data are available on structurally-related substances. Thus, read-across based on a category approach was conducted.

A reliable bacterial reverse mutation assay (Ames test) was conducted with hydrocarbons, C7-C9, n-alkanes, isoalkanes, cyclics following a protocol similar to OECD 471.The pre-incubation procedure was performed with Salmonella typhimurium strains TA 1535, TA 1537, TA 1538, TA 98 and TA 100, and Escherichia coli strains WP2 uvr A and WP2.. The strains were exposed to concentrations ranging from 0.31 to 8000 µg/plate for 30 min both with and without metabolic activation prior to plating and further incubation for 48 -72 h.For all strains tested, there was no significant increase in the number of revertants as compared to negative controls. An initial cytotoxicity assay with S. typhimurium TA100 showed that the test substance was extremely cytotoxic, especially in the absence of S9 fraction. Therefore, initial mutation assays were conducted over a low dose range (0.31 -10 µg per mL) with strains TA100 and TA98. Virtually no cytotoxicity was observed at these concentrations, and so more appropriate concentrations were tested for all strains in subsequent assays. Salmonella strains were more sensitive to the cytotoxic effect of the test substance than E. coli strains, and cytotoxicity was greater in the absence of S9-fraction.

In conclusion, the test substance was not mutagenic in this assay (Shell Chemicals, 1983; Brooks et al., 1988).

The potential of hydrocarbons, C7-C9, n-alkanes, isoalkanes, cyclics to cause chromosomal aberrations in rat liver RL4 cells was tested with a method comparable to OECD 473. Cells were exposed to concentrations of 0, 2.5, 5, and 10 µg/mL of test substance for 22 h, and then examined for chromosomal aberrations including polyploidy, chromatid gaps, and chromatid exchanges. Exposure of RL4 cells to 20 µg/mL test substance resulted in inhibition of cell proliferation by 50%. Therefore 10 µg/mL was chosen as the maximum dose level. No significant increase in the frequency of chromosomal damage was observed. Under the conditions of this study, the test material was not clastogenic (Shell Chemicals, 1983; Brooks et al., 1988).

Iso-octane (CAS No. 540-84-1) was tested in a mammalian cell gene mutation assay performed according to OECD 476. The test material was prepared by adding iso-octane at a final concentration of 5 % v/v in culture (DMEM) medium and stirred overnight at room temperature in a foil wrapped, capped parafilm-sealed bottle to saturate the medium. Human lymphoblastoid cells (TK6) were exposed to 100 or 50 % of this saturated DMEM medium with and without metabolic activation for 3 h and allowed for expression for 4 to 8 days. Both with and without metabolic activation, iso-octane did not induce significant increases in the mutation frequency at the thymidine kinase locus and cell survival in iso-octane-saturated medium was greater than 50-60 %. Based on the study design there was no incidence of increased genetic toxicity caused by the test substance (Richardson et al., 1986).

 

In vivo

The in vivo genotoxicity of different category members has been tested.

Hydrocarbons, C7-C9, isoalkanes showed no evidence of genotoxicity in a dominant lethal study with rats. Hydrocarbons, C7-C9, n-alkanes, isoalkanes, cyclics were not clastogenic to mouse bone marrow cells. Iso-octane did not induce unscheduled DNA synthesis in rat hepatocyte cultures.

Based on the category approach, these results suggest that hydrocarbons, C6 -C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane are not expected to induce genotoxicity in vivo.


Short description of key information:
The available data indicate that hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane are not genotoxic.
In vitro:
Negative Ames test with S. typhimurium TA 1535, TA 1537, TA 1538, TA 98 and TA 100, and E. coli WP2 and WP2 uvr A, with and without metabolic activation.
Negative results in mammalian chromosomal aberration and gene mutation tests, the latter with and without metabolic activation.
In vivo:
Negative in dominant lethal, micronucleus and unscheduled DNA synthesis assays.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on read-across from structurally related substances within a category approach, the available data on the genotoxic potential of hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane are conclusive but not sufficient for classification.