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EC number: 905-588-0
CAS number: -
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.
When the petroleum fraction "mixed xylenes"
was tested in the dominant lethal assay in mice, there was no evidence
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)
In vivo data
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.
Limited data is available demonstrating a
lack of genotoxicity of mixed xylene following inhalation in humans
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).
No classification is warranted under DSD or
CLP since all xylene isomers, ethylbenzene and mixed xylene show no
evidence of genotoxicity in vitro or in vivo.
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