Hydrocarbons, C5-C7, n-alkanes, isoalkanes, < 5% n-hexane

Endpoint summary

Additional information

There are no data available on genetic toxicity of hydrocarbons, C5-C6, n-alkanes, isoalkanes, < 5% n-hexane. However, there are reliable data available considered suitable for read-across using the analogue approach.

The target substance is a hydrocarbon solvent with carbon numbers in the range of C5 to C6. The main constituents of the mixed solvent consist of about 43% of C6 species and about 57% of C5 species. n-Hexane is only present in concentrations < 5% of the total volume. The source substances chosen for read-across have similar toxicological properties as the target substance. There is only one distinguishing characteristic for n-hexane. n-Hexane has unique toxicological properties due to its ability to be metabolized to the neurotoxic metabolite 2,5-hexanedione. Other C6 species will not be metabolized to 2,5-hexanedione. For this reason, n-hexane and hydrocarbon solvents containing n-hexane at levels greater than 5% represent a worst case scenario. Taking into account all available data, animal and human toxicity data as well as environmental fate and effects data show that source substances have similar (eco-)toxicological and environmental fate properties as the target substance. Therefore, read-across is performed based on an analogue approach (for details please refer to the analogue justification which is attached in section 13 of the technical dossier).

 

Genetic toxicity: in-vitro data

For n-pentane, strains (TA1535, TA1537, TA98, TA100, and TA1538) of S. typhimurium were exposed to n-pentane at concentrations of 50, 25, 10, 8, 5, 2, or 1% in the presence and absence of mammalian metabolic activation using a modified standard plate test (Kirwin et al., 1980). n-Pentane was not found to be mutagenic at any concentration in both the presence and absence of S9 mix.

In another Ames test, the mutagenicity of vapors of commercial hexane (52% n-hexane) was evaluated in bacteria (API, 1980). According to the study report; plates of S. typhimurium (TA 1535, TA 1537, TA 1538, TA 98, TA 100) were exposed for 7-8 h to test atmospheres of 600, 1000, 3000, 6000 or 9000 ppm of test substance. The test substance did not produce a positive response in any of the test strains with and without metabolic activation.

An in vitro gene mutation assay in mammalian cells was conducted with n-pentane (Pryzgoda, 1997). In this study, Chinese hamster ovary cells were exposed to n-pentane at concentrations of 600, 1000, 1100, 1200, 1300, 1400, or 1500 μg/mL, +S9, and 300, 600, 900, 950, 1000, 1050, or 1100 μg/mL, -S9, for 20 h (initial and confirmatory assay) and 44 h (confirmatory assay). The test material did not induce any biologically significant increase in chromosome aberrations in cultured CHO cells with or without metabolic activation under the conditions of this study. Positive, vehicle, and non-treated controls performed in an appropriate manner, indicating that the test system could detect both activation-dependent and direct-acting mutagens.

Two in-vitro studies determined the genotoxicity of commercial hexane (52% n-hexane) in Chinese hamster ovary (CHO) cells. In one study CHO cells were exposed to concentrations of 0.132, 0.098, 0.063, 0.0362 or 0.0122 µL/mL both with and without metabolic activation for 5 h (API, 1990). The cells were then analyzed for mutation frequency (hypoxanthine-guanine phosphoribosyltransferase test).

The test substance was found not to be mutagenic both in the presence and absence of metabolic activation. However, the test substance was cytotoxic at concentrations of ≥ 0.063 µL/mL.

In the second in-vitro study, CHO cells were exposed to concentrations of commercial hexane (52% n-hexane) of 0.015, 0.034, 0.074, 0.123 and 0.416 µL/mL without metabolic activation and 0.014, 0.022, 0.056, 0.118, and 0.251 µL/mL with metabolic activation (Daughtrey et al., 1994). 0.5 µg/mL triethylenemelamine was used a positive control without metabolic activation and 50 µg/mL cyclophosphamide was used as a positive control with metabolic activation. Negative and positive controls were found to be valid and no significant increase in chromosome aberrations were found. The test substance was however found to be cytotoxic at concentrations of ≥ 0.074 µL/mL. The test substance is not clastogenic.

 

Genetic toxicity: in-vivo data

In a Crl: CDBR rat bone marrow micronucleus assay, 5 animals/sex/dose were administered n-pentane via inhalation at nominal doses of 5000, 10000 or 20000 mg/m³ (Pryzgoda, 1997). Rats were exposed to either n-pentane or air (control) 6 h/day, 5 days/week for 13 weeks. Actual doses received were 5097 ± 97, 10203 ± 151 and 20483 ± 734 mg/m³. n-Pentane did not induce an increase in micronuclei formation at any exposure level when compared to the control group. n-Pentane was tested at an adequate dose because the high dose was half of the lower explosive limit and was the highest dose considered safe to test. The positive control induced the appropriate response.

An in-vivo study determined the effect of inhalation exposure of commercial hexane (52% n-hexane) on rat bone marrow (Daughtrey et al., 1994). Groups of 5 male and 5 female rats were exposed to 900, 3000 and 9000 ppm of test substance vapor for 6 h/day for 5 days. 0.5 mg/kg triethylenemelamine was used as a positive control substance. Animals were sacrificed 3 or 21 h after exposure, and the bone marrow from their femurs examined for cell aberrations. Because no statistically significant increases in cell aberrations were identified, in any of the test groups, the test substance was classified as not genotoxic.

 

All in-vitro and in-vivo studies performed with the source substances n-pentane and commercial hexane showed negative results. Based on the read-across approach, hydrocarbons C5-C6, n-alkanes, isoalkanes, < 5% n-hexane are not considered to be genotoxic.

Short description of key information:
Based on read-across using the analogue approach, hydrocarbons C5-C6, n-alkanes, isoalkanes, < 5% n-hexane are not considered to be genotoxic.

Genetic toxicity: in-vitro data
Gene mutation in bacteria (similar to OECD 471): negative with and without metabolic activation (read-across from n-pentane)
Gene mutation in bacteria (similar to OECD 471): negative with and without metabolic activation (read-across from commercial hexane)
Chromosome aberration (according to OECD 473, CHO cells): negative with and without metabolic activation (read-across from n-pentane)
Chromosome aberration (according to OECD 473, CHO cells): negative with and without metabolic activation (read-across from commercial hexane)
Gene mutation (similar to OECD 476, mouse lymphoma assay): negative with and without metabolic activation (read-across from commercial hexane)

Genetic toxicity: in-vivo data
Chromosome aberration (according to OECD 474, micronucleus assay): negative in Crl:CDBR rats (read-across from n-pentane)
Chromosome aberration (according to OECD 475): negative in Sprague-Dawley rats (read-across from commercial hexane)

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Based on read-across within an analogue approach, the available data on genetic toxicity do not meet the criteria for classification according to Regulation (EC) 1272/2008 or Directive 67/548/EEC, and are therefore conclusive but not sufficient for classification.