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Administrative data

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via inhalation route
Dose descriptor:
NOAEC
2 171 mg/m³
Additional information

Mixed xylene (CAS 1330-20-7) comprises individual xylene isomers (m-xylene, o-xylene, p-xylene) and ethylbenzene.

Non-human information

In a one-generation reproductive toxicity study (Bio/dynamics Inc., 1983), groups of male and female CD rats were exposed to 0, 60, 250, or 500 ppm technical-grade xylene (comprising 2.4% toluene, 12.8% ethylbenzene, 20.3% p-xylene, 44.2% m-xylene, 20.4% o-xylene) by inhalation for 6 hours per day, 5 days per week, for 131 days prior to mating, with exposure continued in females on gestation days (GDs) 1–20 and lactation days 5–20.  The highest exposure level of 500 ppm mixed xylene administered for 6 hours per day for 131 days prior to mating, during mating and continuing through gestation and lactation is a NOAEC for all endpoints measured. There was no evidence of reproductive toxicity in this study. These studies confirm that mixed xylenes and ethylbenzene are not reproductive toxicants.

Human information

No relevant information

Short description of key information:

Available animal data does not provide clear evidence of an adverse effect on sexual function, fertility or development.  

Effects on developmental toxicity

Description of key information

A recent study provides a robust evaluation of the effect of mixed xylene, individual isomers and ethylbenzene on prenatal developmental toxicity at concentrations up to and including 2000 ppm (8684 mg/m3).  The overall NOAEC for maternal effects was 2171 mg/m3 (based on reduced body weight gain and food consumption) and the overall  NOAEC for foetal effects was 434 mg/m3 based on reduced body weight.   An earlier study by Hass (1993) confirms the lack of effect of 200 ppm on foetal body weight and thus the NOAEC for foetal effects is 868 mg/m3.

A series of three studies to evaluate the effect of mixed xylene on post natal development was undertaken using concentrations of 868 and 2171 mg/m3 were unable to determine a sufficiently robust LOAEC or NOAEC. However, a robust and well conducted study of ethylbenzene over 2 generations at concentrations of 100 and 500 ppm confirmed the lack of effect on physical and neurobehavioural development of the offspring.

There is some evidence that toluene causes lower body weight at birth and delayed vaginal opening at exposures (≥ 1000 ppm) associated with slight maternal toxicity. The NOAEC for developmental and maternal effects is 600 ppm (2261 mg/m3).

Effect on developmental toxicity: via inhalation route
Dose descriptor:
NOAEC
868 mg/m³
Additional information

Mixed xylene (CAS 1330-20-7) comprises individual xylene isomers (m-xylene, o-xylene, p-xylene) and ethylbenzene. Data for these substances and the component substances benzene, toluene and styrene have been considered in this summary.

A well documented comparative standard prenatal developmental toxicity study (Saillenfait et al, 2003) evaluated each of the xylene isomers, mixed xylene and ethylbenzene . Sprague Dawley rats were exposed whole-body to m-, o- or p-xylene, mixed xylene (15.3% ethylbenzene, 21.3% o-xylene, 43.9% m-xylene, 19.4% p-xylene ) or ethylbenzene at nominal atmospheric vapour concentrations of 0, 100, 500, 1000, or 2000 ppm for 6 hours/day from gestation days 6-20. Maternal toxicity was observed (reduced body weight gain and food consumption) for each substance at 1000 and 2000 ppm. The no observed-adverse effect concentration (NOAEC) for maternal toxicity was 500 ppm / 2171 mg/m3. 

Lower foetal body weights were observed in the presence of maternal toxicity in all instances.  There was no indication of any teratogenic effect in this study and no indication of foetal dysmorphogenesis.  The NOAEC for developmental toxicity was 100 ppm / 434 mg/m3 for o- and mixed xylene and 500 ppm / 2171 mg/m3 for m- and p-xylene and also ethylbenzene, based on lower foetal body weights. 

This study provides a robust evaluation of the effect of the individual xylene isomers, mixed xylene and ethylbenzene on prenatal developmental toxicity at concentrations up to and including 2000 ppm / 8684 mg/m3. The overall NOAEC for foetal effects was 434 mg/m3 based on reduced body weight.

The prenatal developmental toxicity of mixed xylene was also assessed by Hass, (1993). In this study pregnant female rats were exposed whole-body to nominal atmospheric vapour concentrations of 0 or 200 ppm for 6 hours/day from gestation days 4-20.  200 ppm was a NOAEC for maternal toxicity.  Delayed ossification of the os maxillare was significantly increased in litters from treated dams and was judged to be treatment-induced. However, the definitive assessment of Saillenfait clearly demonstrates the absence of this finding at lower and higher concentrations of the mixed xylenes and xylene isomers and the increased incidence of this single finding is therefore considered to be incidental to treatment. It should be noted however, that there was no effect of 200 ppm on foetal weight in the Hass 1993 study indicating that the NOAEC of mixed xylenes for developmental toxicity in this study is at least 200 ppm / 868 mg/m3.

The postnatal developmental toxicity of mixed xylene was assessed in a series of three studies by Hass et al, (1993, 1995, 1997) using pregnant Wistar rats exposed to a single concentration of xylene by inhalation. In the first study (Hass, 1993) pregnant female rats were exposed whole-body to nominal atmospheric vapour concentrations of 0 or 200 ppm for 6 hours/day from gestation days 4-20.  200 ppm was a NOAEC for maternal toxicity. The pups born from exposed mothers had a higher body weight, and were therefore more advanced in the development of some physical milestones. They exhibited impaired motor ability (Rotarod test) when assessed at 22-24 days of age. However, in the report of the second study, (Hass et al, 1995) the possibility of bias due to the testers not being ‘blind’ to the exposure status of the animals was noted and no clear effect of 500 ppm on rotarod performance was established. Thus, Hass et al, (1993) did not identify a reliable developmental NOAEL or LOAEL.

In the second study (Hass, 1995), pregnant female rats were exposed whole-body to nominal atmospheric vapour concentrations of 0 or 500 ppm for 6 hours/day from gestation days 7-20. 500 ppm was a NOAEC for maternal toxicity.  Assessment of post-natal development of the pups included reflex development, neurobehavioural/neuromotor ability and learning/memory. One male and one female from each litter were kept in pairs of the same sex in standardized housing from 22 days of age until 3 months, when they underwent the Morris water maze test.  Another male and female from each litter were kept in enriched housing, 4-5 per sex per cage (cages contained various toys) and tested for rotarod (the ability to remain on a rotating rod for 30 seconds), open field, and Morris maze performance at about 3 months of age. A non-statistically significant decrease in rotarod performance was reported in exposed female pups. Offspring from xylene-exposed rats that were raised in the enriched environment showed no difference in the Morris maze test when compared with controls but offspring from exposed rats that were raised in the standard housing had impaired performance. At 16 weeks, exposed offspring took more time to find a platform hidden in the centre of the pool; the effect was limited to the female offspring from the standard housing. These females had an increase in swimming length, but swim speed was unaffected.

In the third study (Hass, 1997) pregnant female rats were exposed whole-body to nominal atmospheric vapour concentrations of 0 or 500 ppm for 6 hours/day from gestation days 7-20. 500 ppm was a NOAEC for maternal toxicity. Post-natal learning and memory abilities (Morris water maze test) were assessed in female offspring in standard housing conditions at 28 and 55 weeks of age. At 28 weeks, an increased latency for finding a platform that was moved to a new position was observed only during the first trial of a three-trial testing block, whereas the next two trials resulted in similar latencies between exposed and control rats. The increased latency again corresponded with increased swimming length. There were no differences at 55 weeks.

The results of the second and third studies suggested that prenatal exposure to 500 ppm xylenes, 6 hours per day on GDs 7–20 affected the performance of standard housing female rats in the Morris water maze test; a longer time was taken to find a hidden platform as swim length (i.e. the distance covered before finding the platform) was increased and swim speed was unaffected. The data suggest this is not a motor effect but a minimal effect on neurological development which was reversible. There were limitations in the design and/or reporting of these studies, including the use of only one concentration of mixed xylene in each. In addition, effects were only seen in one sex, were mitigated by differences in housing conditions and did not reflect an inability of animals to learn or recall the task as all animals reached the platform. Consequently this minor, reversible effect on performance is considered to be insufficiently robust to be used to determine a LOAEC.

A recent and well conducted 2-generation study on ethylbenzene included an evaluation of several developmental landmarks in the F1 and F2 offspring and an assessment of developmental neurotoxicity in the F2 offspring (Faber, 2006 & 2007). Concentrations of 0, 25, 100 or 500 ppm ethylbenzene were administered by inhalation for 6 hours /day throughout the study (except on lactation days 1-4 inclusive when the equivalent dose was administered to the parent females by oral gavage). The following physical developmental landmarks: pinna detachment, hair growth, incisor eruption and eye opening were assessed prior to weaning and vaginal patency and balano-preputial separation were assessed post weaning. There was no adverse effect of ethylbenzene on the acquisition of these landmarks in either the F1 or F2 generations. For the F2 generation, neurobehavioral development of one pup/sex/litter was also evaluated using the functional observational battery (on postnatal days 4, 11, 22, 45, and 60), motor activity (on postnatal days 13, 17, 21, and 61), acoustic startle testing (on postnatal days 20 and 60), Biel water maze learning and memory task (initiated on postnatal days 26 or 62). Whole-brain measurements, brain morphometric and histologic assessments were also conducted on postnatal days 21 and 72. No treatment-related effects were observed. The results of this 2 generation study, corroborate the results of the developmental toxicity study of Saillenfait (2003), which also included exposure concentrations of 100 and 500 ppm ethylbenzene, in that there was no effect on the number of live foetuses or mean foetal weight and similarly no effect on the number of live pups per litter or mean pup body weight. Although ethylbenzene was not evaluated by Hass (1993, 1995 or 1997), the results of the 2-generation study provide good evidence in support of the lack of effect of mixed xylenes on neurobehavioural development or on brain development.

The mixed xylenes and ethylbenzene are not developmental toxicants.

The available data on potential specific components benzene and styrene have also been considered. Of these only data on toluene indicates evidence of developmental toxicity:

Toluene (Classification: EU – Harmful Xn, R63; GHS/CLP – Category 2, H361d): There is no evidence that toluene produces malformation in animals or humans. There is some evidence of developmental toxicity (lower body weight at birth and delayed vaginal opening) at toluene exposure concentrations ≥ 1000 ppm, concentrations which are associated with slight maternal toxicity. The NOAEC for developmental and maternal effects is 600 ppm (2261 mg/m3) (Thiel and Chahoud, 1997).

 

Justification for classification or non-classification

Mixed xylenes, xylene isomers and ethylbenzene do not warrant classification for reproductive or developmental toxicity according to DPD or CLP. There are sufficient data available on component substances to conclude that streams within this class that contain less than 5% (DPD) or 3% (CLP) toluene are not reproductive or developmental toxicants and do not require a label for these endpoints.

Mixed xylene streams which contain ≥3% toluene should be classified Category 2, H361d “Suspected of damaging the unborn child” according to CLP. Toluene may be present at a maximum 5% and, at that level, streams should be classified: Xn, Cat 3 R63 “Possible risk of harm to unborn child”, according to DPD.

Additional information