Registration Dossier

Administrative data

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route
Endpoint conclusion:
no study available
Effect on fertility: via inhalation route
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEC
2 171 mg/m³
Species:
rat
Quality of whole database:
Studies conducted in rats demonstrate no evidence that mixed xylene or ethylbenzene adversely affect reproduction.
Effect on fertility: via dermal route
Endpoint conclusion:
no study available
Additional information

The multi-constituent substances covered by this registration comprise individual xylene isomers (m-xylene, o-xylene, p-xylene) and ethyl benzene (>10% - <20%). The following information is available to characterise their effects on fertility.

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% ethyl benzene, 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 from this study that mixed xylene containing 12.8% ethyl benzene is a reproductive toxicant.

Additional information is available on ethyl benzene. Similarities in the physicochemical and toxicological properties of ethyl benzene and xylenes, together with toxicokinetic information indicating that biotransformation proceeds primarily via hydroxylation of the alkyl side chain followed by urinary excretion of conjugated metabolites, suggests that read-across between these structures is scientifically justifiable. (See section 13 of the IUCLID dossier for further details.)

In a 2-generation study conducted on ethyl benzene (Faber et al., 2006), male and female Crl:CD(SD)IGS BR rats were exposed by inhalation to 0, 25, 100 or 500 ppm ethyl benzene vapour (for 6 hr/day) for at least 70 consecutive days prior to mating, with exposure of the females continuing through gestation up to GD20 after which ethyl benzene was administered via oral gavage (26, 90 or 342 mg/kg/day in corn oil) on lactation days 1 and 4. The gavage treatment was designed to provide a similar maternal blood concentration (AUC) to that achieved by inhalation. At 500 ppm ethyl benzene, the males of both generations showed reduced body weight gain and increased liver and kidney weights whilst in high dose females only liver weights were affected. As the reduced body weight gain in the 500 ppm males was transient, and since there were no histopathological changes associated with the increased organ weights found in the 500 ppm males and females, these changes were considered not to be adverse. Therefore, for parental systemic toxicity the NOEC was considered to be 100 ppm and the NOAEC 500 ppm. There were no adverse effects of ethyl benzene on reproductive performance in either generation, nor were spermatogenic endpoints, ovarian follicle counts, reproductive organ weights or macroscopic pathology affected. The NOAEC for reproductive toxicity and offspring development was 500 ppm ethyl benzene.

Overall these studies provide no evidence that mixed xylene or ethyl benzene have a potential to adversely affect reproduction in the rat. A NOAEC greater than 500 ppm (greater than 2171 mg/m3) was obtained in both instances.

Human information

No relevant information


Short description of key information:
Available animal data provide no evidence of an adverse effect on sexual function, fertility or development.

Justification for selection of Effect on fertility via inhalation route:
No adverse effects on sexual function, fertility or development were apparent in a rat one generation study conducted on mixed xylene (NOAEC exceeds 2171 mg/m3; Bio-Dynamics, 1983). A two generation study on ethylbenzene was also negative (NOAEC 2171 mg/m3; Faber et al., 2000).

Effects on developmental toxicity

Description of key information
Information is available on the effect of mixed xylene on prenatal development in rats exposed to concentrations up to and including 2000 ppm (8684 mg/m3). The results indicate that maternal toxicity (reduced corrected maternal body weight gain) occurred at exposures that were lower than those causing a biologically meaningful (>10%) reduction in foetal body weight, indicating that mixed xylene is not selectively toxic towards the foetus. 
Effect on developmental toxicity: via oral route
Endpoint conclusion:
no study available
Effect on developmental toxicity: via inhalation route
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
BMCL10
4 698 mg/m³
Study duration:
subchronic
Species:
rat
Quality of whole database:
Studies conducted in rats provide no evidence that mixed xylene is selectively toxic to the foetus.
Effect on developmental toxicity: via dermal route
Endpoint conclusion:
no study available
Additional information

The multi-constituent substances covered by this registration comprise individual xylene isomers (m-xylene, o-xylene, p-xylene) and ethyl benzene (>10% - <20%). The following information is available to characterise their effects on foetal development.

A well-documented guideline study (Saillenfait et al, 2003) evaluated the developmental toxicity of mixed xylene (comprising 15.3% ethyl benzene, 21.3% o-xylene, 43.9% m-xylene, 19.4% p-xylene); m-, o- and p-xylene isomers; and ethyl benzene in Sprague Dawley rats following whole-body exposure to nominal vapour concentrations of 0, 100, 500, 1000, or 2000 ppm for 6 hours/day from gestation days (GD) 6-20. For rats exposed to mixed xylene, there was a dose-dependent decrease in maternal corrected body weight gain (body weight gain during GD 6-21 minus gravid uterine weights), including a 33% decrease in corrected body weight gain at 1000 ppm, although statistical significance was achieved only at 2000 ppm (-97% reduction compared to control rats). Maternal food consumption during GD 6-21 were also reduced at 1000 (-8% compared to controls) and 2000 ppm (-16% compared to controls), although statistical significance was only seen at the highest dose group. Lower foetal body weights were observed in all treatment groups, with statistically significant reductions observed at higher exposures (-4% at 500 ppm; -7% at 1000 ppm; -16% at 2000 ppm). However it is noted that the magnitude of some of these changes was small (<10%), suggesting that their biological relevance is limited. There was no indication of any teratogenic effect in this study and no indication of foetal dysmorphogenesis. Dose-response data for foetal body weights and corrected maternal weight gain from this study were subsequently analyzed by the Registrant using Benchmark Dose (BMD) modelling software developed by US-EPA (2013). The intention was to better characterize exposure levels associated with biologically relevant reductions in foetal weight and maternal corrected body weight gain. The data were analyzed using a range of models included in the software package, and tested for goodness-of-fit using a chi-square goodness-of-fit test (Chi-square p-value < 0.10 indicated inadequate fit). The best-fit model was selected, and the BMCL10 (reflecting the 90% lower confidence limit on the BMD) calculated. The underling calculations are included in the IUCLID dataset. The results showed that the BMCL10 for maternal toxicity (assessed as a decrease in corrected body weight gain) was 887 ppm for mixed xylene (equivalent to 3851 mg/m3) and in a range 616 - 898 ppm for the individual xylene isomers; the BMCL10 for foetal effects (assessed as a decrease in foetal weight) was 1082 ppm for mixed xylene (equivalent to 4698 mg/m3) and 965 – 1306 ppm for the individual isomers. Hence maternal toxicity occurred at exposures that were lower than those causing a biologically meaningful (>10%) reduction in foetal body weight indicating that mixed xylene (and other xylene isomers) are not selectively toxic towards the foetus.

The prenatal developmental toxicity of mixed xylene was also assessed by Hass and Jakobsen (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. No adverse effects were apparent in the dams, hence 200 ppm was the NOAEC for maternal toxicity. Delayed ossification of the os maxillare was significantly increased in litters from treated dams and was judged by the study authors to be treatment-induced. However, since the definitive assessment of Saillenfait clearly demonstrates the absence of this finding following exposure to higher (and lower) concentrations of both mixed xylene and xylene isomers it is therefore considered to be incidental to treatment.

With regard to any potential effect of in utero exposure to mixed xylene on foetal body weight, Hass and Jakobsen (1993) found no difference in weight at birth for female pups, while male pup body weights were slightly (+8%; statistically significant) increased in litters from the 200 ppm treatment group. Since this level of exposure is intermediate between the low- and no effect level for foetal body weight effects reported by Saillenfait et al, 2003), it indicates that the NOAEC for developmental toxicity of mixed xylene 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 and Jakobsen, 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. As noted above, 200 ppm was a NOAEC for maternal toxicity. Some deterioration in Rotorod test performance was reported for treated females on PND 22, 23 and 24 while the results for treated males were indistinguishable from those of the controls. However when discussing these findings the study authors note that “the animals were not tested blindly to exposure group and not on the same day. Therefore, a possible influence from the experimenter cannot be totally excluded”, hence no reliable LOAEC or NOAEC can be derived from the study.

In the second study (Hass et al., 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. No maternal effects were apparent at 500 ppm, which is therefore 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 et al., 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 ethyl benzene included an evaluation of several developmental landmarks in the F1 and F2 offspring and an assessment of developmental neurotoxicity in the F2 offspring (Faber et al., 2006; 2007). Similarities in the physicochemical and toxicological properties of ethyl benzene and xylenes, together with toxicokinetic information indicating that biotransformation proceeds primarily via hydroxylation of the alkyl side chain followed by urinary excretion of conjugated metabolites, suggests that read-across between these structures is scientifically justifiable. (See section 13 of the IUCLID dossier for further details.)

In this investigation, concentrations of 0, 25, 100 or 500 ppm ethyl benzene 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 ethyl benzene 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 et al. (2003), which also included exposure concentrations of 100 and 500 ppm ethyl benzene, 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 ethyl benzene was not evaluated by Hass and co-workers (1993; 1995; 1997), the results from the 2-generation study provide good evidence in support of the lack of effect of mixed xylenes on neurobehavioural development or on brain development. Overall it is concluded that mixed xylene and ethyl benzene are not developmental toxicants.


Justification for selection of Effect on developmental toxicity: via inhalation route:
Information is available on the effect of mixed xylene on prenatal development in rats exposed to concentrations up to and including 2000 ppm (8684 mg/m3; Saillenfait et al., 2003). Analysis of dose-response data for foetal body weights and corrected maternal weight gain using Benchmark Dose (BMD) modelling software developed by US-EPA showed that the BMCL10 for foetal effects (assessed as a decrease in foetal weight) was 1082 ppm (4698 mg/m3), and the BMCL10 for maternal toxicity (assessed as a decrease in corrected body weight gain) was 887 ppm (3851 mg/m3). Hence maternal toxicity occurred at exposures that were lower than those causing a biologically meaningful (>10%) reduction in foetal body weight, indicating that mixed xylene and xylene isomers are not selectively toxic towards the foetus.

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 are not reproductive or developmental toxicants and do not require a label for these endpoints.