Xylene

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vivo

Description of key information

Available data from both in vitro and in vivo studies indicate that the xylene isomers have no significant genotoxicity.

Link to relevant study records

Reference

Endpoint:

in vivo mammalian germ cell study: cytogenicity / chromosome aberration

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not specified

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP near guideline study, available as unpublished report, minor restrictions in design and/or reporting but otherwise adequate for assessment.

Justification for type of information:

N/A

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 478 (Genetic Toxicology: Rodent Dominant Lethal Test)

Deviations:

no

Principles of method if other than guideline:

Male mice of confirmed fertility were given a subcutaneous injection of 1.0 mL/kg mixed xylenes (diluted 10% in corn oil) and each housed with 3 virgin females for a period of 1 week. At the end of the week, the males were transferred to new groups of virgin females and the process repeated for a total of 8 weeks (the time of one complete sperm cycle). The females were killed on the 15th day following first contact with the male and the uteri examined for early and late deaths and total implants.

GLP compliance:

no

Type of assay:

rodent dominant lethal assay

Specific details on test material used for the study:

not specified

Species:

mouse

Strain:

Swiss Webster

Details on species / strain selection:

not specified

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Simonsen Laboratories, Gilroy, California
- Age at study initiation: approx 10 weeks
No further details available

ENVIRONMENTAL CONDITIONS: No data

IN LIFE DATES: No data

Route of administration:

subcutaneous

Vehicle:

- Vehicle(s)/solvent(s) used: corn oil

Details on exposure:

not specified

Duration of treatment / exposure:

Single injection to male mice immediately prior to initial mating.

Frequency of treatment:

Single injection

Post exposure period:

eight weeks (of mating)

Dose / conc.:

1 other: mL/kg

No. of animals per sex per dose:

10 males each mated with 3 females, males transferred to a new group of females at the end of a week for a total of 8 weeks (i.e. 240 females)

Control animals:

yes, concurrent vehicle

Positive control(s):

triethylenephosphoramide (TEPA)
- Doses / concentrations: 7 mg/kg

Tissues and cell types examined:

Uteri examined for early and late deaths and total implants.

Details of tissue and slide preparation:

not specified

Evaluation criteria:

The weekly data from females was compiled to calculate the following indices (weekly and total based on entire 8 week cycle): pregnancy index (% pregnant) and mutagenic index.

Statistics:

Chi square tests were carried out on the ratios representing total fertility and mutagenic indices for comparison of each group with the negative control. In addition, Chi square tests were run on any unusual weekly index and on any weekly mutagenic index greater than 10. Mutagenic indices below 10 are well within the normal range.

Key result

Sex:

male

Genotoxicity:

negative

Toxicity:

not specified

Vehicle controls validity:

valid

Negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

N/A

No deviations from vehicle control values, except for a significantly reduced mutagenic index during the 3rd week of mating which resulted from an unusually high control value and was therefore considered not to be treatment-related. No evidence of decreased pregnancy rate or increased embryo loss.

Conclusions:

Interpretation of results: negative
When the petroleum fraction "mixed xylenes" was tested in the dominant lethal assay in mice, there was no evidence of mutagenicity.

Executive summary:

When the petroleum fraction "mixed xylenes" was tested in the dominant lethal assay in mice, there was no evidence of mutagenicity.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

In vitro data

The xylene isomers and mixed xylenes have been examined for activity on both gene mutation and cytogenetic endpoints. None of the xylene isomers was mutagenic in bacterial mutagenicity assays using Salmonella typhimurium (Haworth, 1983; Bos, 1981; Florin, 1980, Litton Bionetics, 1978a) or Escherichia coli (Shimizu, 1985) either with or without the addition of auxiliary metabolic activation systems.  Litton Bionetics (1978a) also reported negative results for gene mutation from the evaluation of mitotic recombination in Saccharomyces cerevisiae. In assays examining for chromosomal effects in mammalian cells, mixed xylene (composition unspecified) did not induce either sister chromatid exchanges or chromosomal aberrations in Chinese hamster ovary cells (Anderson, 1990) or gene mutation in mouse lymphoma L5178Y cells (Litton Bionetics, 1978a).  

A recent assay examining the effect of various substances for DNA damage in vitro using the alkaline and neutral comet assays (Chen, 2008), the authors reported increases in DNA strand breaks on isolated human peripheral blood lymphocytes exposed to m-, o- or p-xylene. Their investigations suggested that reactive oxygen species may play a role in the damage observed. The relevance of the small changes possibly due to active oxygen species observed in isolated lymphocytes is considered limited.  In particular, no evidence to support a consequence of any radical-induced damage was seen in a cytogenetic assay (Anderson, 1990). In view of the available studies including the key endpoints of gene mutation and chromosomal damage, additional in vitro assays of the genotoxicity potential of xylenes are considered unnecessary.

In vivo data

Non-human information

The xylene isomers do not induce micronuclei in the bone marrow of mice after two intraperitoneal doses in the range 105 – 650 mg/kg b. w. (Mohtashamipur, 1985). Mixed xylenes do not induce chromosome aberrations in the bone marrow of treated rats (0.044, 0.147 and 0.441 mL/kg by intraperitoneal injection, equivalent to approximately 39, 129 and 388 mg/kg), Litton Bionetics (1978a). A negative result was obtained for mixed xylenes in dominant lethal assays conducted in rats and mice (Hine Laboratories Inc., 1973).

Human information

No data are available regarding the potential genotoxicity of m-xylene, o-xylene or p-xylene in humans following inhalation, oral or dermal exposure has been sourced. Limited data is available demonstrating a lack of genotoxicity of mixed xylenes following inhalation in humans (ATSDR, 2007).

Conclusion

In view of the lack of significant genotoxicity observed in the in vitro studies, and the available negative results examining for chromosomal damage in vivo, mixed xylenes and the individual isomers are considered not to have genotoxic potential.

Justification for selection of genetic toxicity endpoint
Available data indicate that the xylene isomers have no significant genotoxicity in bacterial and mammalian systems in vitro and/or in vivo.

Justification for classification or non-classification

No classification is warranted under CLP since all xylene isomers show no evidence of genotoxicity in vitro or in vivo.