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Administrative data

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 mixed xylene has no significant genotoxicity.

Link to relevant study records
Reference
Endpoint:
in vivo mammalian germ cell study: cytogenicity / chromosome aberration
Remarks:
Type of genotoxicity: chromosome aberration
Type of information:
experimental study
Adequacy of study:
key study
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other: Non-GLP near guideline study, available as unpublished report, minor restrictions in design and/or reporting but otherwise adequate for assessment.
Qualifier:
equivalent or similar to
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
Species:
mouse
Strain:
Swiss Webster
Sex:
male/female
Details on test animals 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
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)
Remarks:
Doses / Concentrations:
1.0 mL/kg
Basis:

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.
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.
Sex:
male
Genotoxicity:
negative
Vehicle controls validity:
valid
Negative controls validity:
not applicable
Positive controls validity:
valid

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 (migrated information): 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

Additional information from genetic toxicity in vivo:

Mixed xylene (CAS 1330-20-7) comprises individual xylene isomers (m-xylene, o-xylene, p-xylene) and <10% ethylbenzene. The following information is available to characterise the genotoxic potential of this substance.

In vitro data

Mixed xylene has been examined for activity on both gene mutation and cytogenetic endpoints. A sample comprising 52% m-xylene, 11% o-xylene, 36% ethyl benzene was not mutagenic in bacterial mutagenicity assays using Salmonella typhimurium (Litton Bionetics, 1978). 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, 1978). Litton Bionetics (1979) also reported negative results for gene mutation from the evaluation of mitotic recombination in Saccharomyces cerevisiae. A recent assay examining for DNA damage, the comet assay (Chen, 2008), reported increases in fragmentation when isolated human peripheral blood lymphocytes were exposed to levels of 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 mixed xylene are considered unnecessary, as also concluded by the recent ATSDR (2007) review.

In vivo data

Non-human information

Mixed xylene (comprising 52% m-xylene, 11% o-xylene, 36% ethyl benzene) did not induce chromosome aberrations in the bone marrow of treated rats (0.044, 0.147 and 0.441 cc/kg by intraperitoneal injection), Litton Bionetics (1978). A negative result was obtained for mixed xylene in dominant lethal assays conducted in rats and mice (Hine Laboratories Inc., for API, 1973). 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 xylene is considered not to have genotoxic potential.

Human information

Limited data is available demonstrating a lack of genotoxicity of mixed xylene following inhalation in humans (ATSDR, 2007).

The genotoxicity of ethyl benzene is reviewed in the recent RAR (2008) and it was concluded from various in vitro and in vivo mutagenicity tests that there is no relevant indication that ethyl benzene is genotoxic. The same conclusion has been drawn for xylene isomers in the recent comprehensive review of ATSDR (2007). Neither ethyl benzene or any of the xylene isomers are classified for mutagenicity under the DSD (Dir. 67/548/EEC). DSD in no longer applicable.


Justification for selection of genetic toxicity endpoint
Negative results were obtained for mixed xylene when tested in a dominant lethal assay in rats, and also in a complementary assay assay conducted in mice (Hine Laboratories Inc., 1973). Results from an in vivo rat bone marrow chromosome aberration assay on mixed xylene were also negative (Litton Bionetics, 1978). In vitro genetic toxicity data for xylene isomers are also consistently negative.

Justification for classification or non-classification

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