Ethylbenzene

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

4 342.13 mg/m³

Study duration:

subacute

Species:

rat

Additional information

No human data are available.

 

In a guideline 2-generation study in rats by inhalation, no effects on reproduction or developmental endpoints were noted at exposure levels up to and including 500 ppm with minimal parental toxicity at this exposure level (decreased body weight, increased liver weight) (Faber et al., 2006; WIL Research Laboratories, Inc., 2005). In the preceding 1-generation probe study no effects on reproduction were found up to and including 1000 ppm, whereas effects on the offspring (reduced postnatal survival and reductions in mean body weight gain) development were observed at levels > 500 ppm (WIL Research Laboratories, Inc., 2003). A slight but mostly not significant reduced mean body weight was even noted in the F1 weanlings exposed to 100 ppm beginning on postnatal day 22 in both the inhalation (4-14%) and inhalation/gavage (6-16%) groups.

 

The results from the functional tests on fertility with the 1- and 2-generation studies are supported by the results from repeated dose toxicity studies without adverse findings by weight and histopathology of reproductive organs, sperm parameters and estrous cyclicity. No such adverse effects were found in guideline studies after 13 weeks of inhalation at 1000 ppm (NTP, 1992), after 2 years of inhalation at 750 ppm (apart from possibly neoplastic related testicular effects) (NTP, 1999) and after 13 weeks of oral gavage application at 750 mg/kg bw (BASF, 2004; Mellert et al., 2007). A NOAEC/fertility of 1000 ppm (4410 mg/m3) should be used for quantitative risk assessment, which is derived from both the available 1-generation study (WIL Research Laboratories Inc., 2003; Faber et al., 2007) as well as the available guideline according 13 week study (NTP, 1992). For the oral route of exposure a NOAEL/reproductive organ toxicity of 750 mg/kg/d is derived from the available guideline according 13 week study (BASF, 2004; Mellert et al., 2007).

Note- In the study by Wolf et.al (1956), monkeys exposed to 600 ppm ethylbenzene for 186 days (130 exposures) slight generative changes were reported in the testes. The significance of this finding is unclear as the group size was small (either 1 or 2 males tested). and testicular lesions have not been observed in numerous studies of other species even at high exposure levels.

The following information is taken into account for any hazard/risk assessment:

From overall assessment of the available animal data there is no indication for a specific toxic potential adverse to fertility for ethylbenzene. Therefore there is no need for classification and labelling.

Short description of key information:
Reproductive toxicity: fertility impairment (Oral):
No data
Reproductive toxicity: fertility impairment (Dermal):
No data
Reproductive toxicity: fertility impairment (Inhalation):
No adverse effects on fertility were found in a two-generation reproductive toxicity study conducted in rats at 500 ppm and at 1000 ppm in a probe 1-generation study. Furthermore, no adverse effects on reproductive organs were found in a subchronic inhalation study at 1000 ppm.

Effects on developmental toxicity

Description of key information

Reproductive toxicity: developmental toxicity (Oral):
No adverse effects on reproductive organs in a subchronic oral study.
Reproductive toxicity: development toxicity (Dermal):
No data
Reproductive toxicity: development toxicity (Inhalation):
No selective adverse effects on development were noted in the developmental toxicity study in both rats and rabbits.. Slight effects noted only in the 1-generation probe study at 500 ppm were not reproducible in the guideline 2-generation study. The effects in the 1-generation study only occurred in offspring after weaning by direct inhalative exposure.

Effect on developmental toxicity: via oral route

Dose descriptor:

NOAEL

750 mg/kg bw/day

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

434.21 mg/m³

Additional information

As regards potential developmental toxicity of ethylbenzene, animal data from guideline according generation reproductive toxicity studies, prenatal toxicity studies and a developmental neurotoxicity study are available. From the results of these studies there is no indication for substance induced teratogenicity (up to and including 2000 ppm) or developmental toxicity (up to and including 500 ppm). From the prenatal developmental toxicity studies there is indication for slight feto-toxicity (reduced fetal body weight and occasional increases in skeletal variations) in the presence of maternal toxicity (significantly reduced maternal net weight gain) with a NOAEC for fetotoxicity and maternal toxicity of 500 ppm (Saillenfait et al., 2003).

 

Postnatal viability and pup weanling body weight gain, however, revealed to be more sensitive to substance-induced changes in the 1-generation probe study (WIL Research Laboratories, Inc., 2003). The increased postnatal mortality and body weight gain depression in the off-spring of the 1-generation probe study (WIL Research Laboratories, Inc., 2003; Faber et al., 2006), may suggest a NOAEC of 100 ppm (441 mg/m3) for developmental toxicity, which may be considered for use for specific exposure scenarios of the quantitative risk assessment. However, these effects were not reproduced in the subsequent definitive rat 2-generation guideline study (WIL Research Laboratories, Inc., Faber et al., 2006) which supports a NOAEC for fetotoxicity and maternal toxicity of 500 ppm.

 

As a general strategy, the guideline rat 2-generation study with a large number of experimental animals (30/sex/group for F0 and 25/sex/group for F1) should have precedence over the probe study with a limited number of animals for the different investigative subgroups. The aim of the probe study was three fold:

1. To define the exposure levels for the final guideline 2-generation study

2. To determine the feasibility of gavage dosing of dams during lactation days 1-4

3. To determine whether to begin inhalation exposures of weanlings on PND 22 or PND 29 in the 2-generation study.

With an F0 group size of 20 rats/sex/exposure level (0, 100, 500, 1000 ppm) the number of F1 litters in the subgroups with identical treatment was limited. These subgroups in the probe study consisted of 7, 9, 9, and 9 (inhalation only treatment) and of 8, 8, 10, and 10 (inhalation + gavage treatment) (0, 100, 500, and 1000 ppm). The inhalation only females were exposed through gestation day (GD) 20 and on lactation days (LD) 5-27. To avoid confounding effects on nesting and nursing behaviour, exposures for the F0 dams were suspended on GD 21 through LD 4 inclusive. The inhalation + gavage females were exposed via inhalation as above and, in addition, these dams received test subtance or vehicle control (corn oil) on LD 1-4 by gavage. Only these subgroups with identical treatment can be evaluated statistically and these numbers of litters / animals are by far lower than those of the final 2-generation study.

 

The different phases of this probe study have to be assessed regarding their relevance for derivation of exposure limits for workers or the general population related to developmental toxicity. While exposure during pregnancy and lactation (via the milk) might occur in female workers under rare circumstances (e.g. if maternity leave is not taken), it is not possible that inhalation exposure at the workplace will occur in human infants directly after weaning. Therefore, only effects found in offspring until the date of weaning should be taken into consideration to derive a long-term DNEL for workers, but not effects occurring in the offspring exposed by direct inhalation after weaning. Effects observed in offspring exposed in early life phases by direct inhalation are only relevant for an environmental exposure scenario (long-term DNEL for the general population). Therefore the effects observed in the probe 1-generation study have to be separated according to the different phases of early life.

 

Postnatal survival in probe study: Postnatal survival from birth to PND 4 was reduced in the 500 and 1000 ppm groups (inhalation only) and in the 1000 ppm group (inhalation + gavage) compared to control values and the historical control data of the laboratory. These decreases were a result of a total litter loss in the 500 ppm group on PND 0 (inhalation only), one litter in the 1000 ppm group that had 3/13 pups survive through PND 4 (inhalation only), and one litter in the 1000 ppm group that had 4/14 pups survive through PND 4 (inhalation + gavage). None of the differences from the control group were statistically significant. Although total litter losses were observed only in 6 dams in 32 studies of the laboratory, in the absence of other effects on postnatal survival in the 500 ppm groups (inhalation only and inhalation + gavage) on PND 0, this total litter loss was unlikely due to ethylbenzene exposure. In contrast, the reductions noted in postnatal survival through PND 4 in the 1000 ppm groups occurred both in the inhalation only and inhalation + gavage phases in the presence of other adverse effects (reduced pup weights) and were likely due to maternal exposure. Following culling on PND 4, postnatal survival in both the inhalation and inhalation + gavage groups were similar to the control group with the exception of a single total litter loss in one litter in the 100 ppm group (inhalation only) on lactation day 15. In conclusion, the NOAEC for postnatal mortality up to weaning is 500 ppm.

 

Body weight in probe study: Mean male and female pup body weights in the 1000 ppm group were significantly lower than the control group values on PND 1. The reductions continued through PND 28 for the 1000 ppm group (inhalation + gavage) that were statistically significant on PND 1, 14, and 21. The same trend was observed for mean body weight gains in the 1000 ppm group (inhalation + gavage) for the periods of PND 7-14, 14-21, and 21-28, the difference being statistically significant on PND 7-14 in comparison to the control group. Statistically significant decreases in mean body weight gain compared to the control group were also observed for males in the 100 and 500 ppm groups (inhalation + gavage) for the period PND 7-14. However, unlike the 1000 ppm group, the reductions in body weight gain for the 100 and 500 ppm groups did not persist during PND 14-21 and 21-28. Thus, as regards body weight development of offspring until weaning the NOAEC is 500 ppm.

 

The effects observed in the probe study on offspring after direct inhalation exposure are only briefly summarized without going into detail, as these are not considered relevant for derivation of a long-term DNEL for workers, but only for the DNEL for the general population exposed via the environment. One and two weanlings in the 500 and 1000 ppm (inhalation only) groups, respectively, and four weanlings in the 1000 ppm (inhalation + gavage) group were found dead or euthanized in extremis between PND 22 and 26. These mortalities were considered to be exposure-related. Reductions in body weight and/or body weight gain, that could be attributed to exposure, were observed in the 1000 and 500 ppm groups (inhalation only and inhalation + gavage) for weanlings with inhalation exposure on PND 22-33 and on PND 29-33. In addition slightly reduced mean body weights were found in the 100 ppm groups (inhalation only and inhalation + gavage) for the inhalation exposure during PND 22-33, that were considered potentially due to test subtance exposure. Thus, the NOAEC for offspring exposed by inhalation already in an early life phase is 100 ppm.

 

In summary, the NOAEC for developmental effects relevant for the exposure situation at the workplace is 500 ppm and that relevant for the general population exposed via the environment 100 ppm with an exposure schedule of 6h/d; 7 d/week. It should be noted that the application of the NOAEC from the probe 1-generation study for derivation of the long-term DNEL general population is clearly on the conservative side, as the definitive guideline 2-generation study gave a higher NOAEC of 500 ppm.

 

From overall assessment of the available animal data there is no indication for a specific toxic potential adverse to development (physical and neurological) for ethylbenzene. Therefore, there is no need for classification and labelling.

The following information is taken into account for any hazard/risk assessment:

From overall assessment of the available animal data there is no indication for a specific potential adverse to fertility and/or (physical and neurological) development. Thus there is no need for classification and labelling.

Justification for selection of Effect on developmental toxicity: via inhalation route:
No selective adverse effects on development were noted in the developmental toxicity study in both rats and rabbits. Slight effects noted only in the 1-generation probe study at 500 ppm were not reproducible in the guideline 2-generation study. The effects in the 1-generation study only occurred in offspring after weaning by direct inhalative exposure.

Justification for classification or non-classification

Toxicity to reproduction- fertility:

 

In a guideline 2-generation study in rats by inhalation, no effects on reproduction were noted at exposure levels up to and including 500 ppm with minimal parental toxicity at this exposure level (decreased body weight, increased liver weight). The results from the functional tests on fertility in the 2-generation study are supported by repeated dose toxicity studies without adverse findings by weight and histopathology of reproductive organs, sperm parameters and estrous cyclicity. Thereby no such adverse effects were found in guideline studies after 13 weeks of inhalation at 1000 ppm, after 2 years of inhalation at 750 ppm and after 13 weeks of oral gavage application at 750 mg/kg bw.

 

Therefore, classification for reproductive-fertility toxicity is not warranted in accordance with Directive 67/548/EEC,EU CLP (Regulation (EC) No. 1272/2008) and UN GHS.

 

Toxicity to reproduction- development:

 

As regards potential developmental toxicity of ethylbenzene, data from a 2-generation study, prenatal toxicity studies and a developmental neurotoxicity study are available in rats, each according to the present guidelines. From the results of theses studies there is no indication for substance induced teratogenicity (up to and including 2000 ppm) or developmental toxicity including a specific investigation of developmental neurotoxicity (up to and including 500 ppm). From the prenatal developmental toxicity studies there is indication for slight feto-toxicity (reduced fetal body weight and occasional increases in skeletal variations) in the presence of maternal toxicity (significantly reduced maternal net weight gain) with a NOAEC for fetotoxicity and maternal toxicity of 500 ppm.

 

A probe 1-generation study was carried out in rats for dose selection and defining details for the guideline 2-generation study. This probe study gave an indication of reduced postnatal viability and body weight gain in offspring at 500 ppm with a NOAEC of 100 ppm. But the results must be interpreted with caution as they could not be reproduced in the guideline 2-generation study. Furthermore, these findings were limited to the time after weaning when the offspring was exposed to ethylbenzene by direct inhalation, but did not occur in the time span between birth and weaning. Therefore, these effects, if real at all, would only relate to the very low environmental exposures but not to the workplace.

 

Based on the absence of adverse effects on development in these studies, classification for reproductive-developmental toxicity is not warranted in accordance with Directive 67/548/EEC,EU CLP (Regulation (EC) No. 1272/2008) and UN GHS.

 

Toxicity to reproduction - breastfed babies:

 

There were no effects on offspring in the available guideline 2-generation study in rats. In the probe 1-generation study carried out for dose selection and defining details for the guideline 2-generation study there was an indication of reduced postnatal viability and body weight gain in offspring at 500 ppm with a NOAEC of 100 ppm. These findings were limited to the time after weaning when the offspring was exposed to ethylbenzene by direct inhalation, but did not occur in the time span between birth and weaning. Therefore, these effects were not related to the nursing period.

 

In conclusion, classification for reproductive-breastfed babies is not warranted in accordance with Directive 67/548/EEC,EU CLP (Regulation (EC) No. 1272/2008) and UN GHS.