Ethylbenzene

Endpoint summary

Description of key information

The repeated exposure toxicity of ethylbenzene has been evaluated in animals in subchronic and chronic inhalation studies, subchronic oral toxicity studies and numerous specialized investigations. Overall, ethylbenzene poses a moderate repeated exposure toxicity hazard with consistent targeted effects to the liver, kidney and hearing.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

75 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

500 mg/m³

Additional information

Oral route

 

Data obtained after oral exposure support the main findings of inhalation studies. The most comprehensive investigation is that of Mellert et al. (2007) (BASF, 2004) exposing rats by gavage at levels of 75, 250 and 750 mg/kg bw/d over 90 days. Body weight was significantly decreased in males at 750 mg/kg bw/ d. Liver and kidney weights were increased at 250 and 750 mg/kg bw/d accompanied by slight centrolobular hypertrophy, those in the kidney are characterised as chronic progressive nephropathy and accumulation of male specific protein α-2u-globulin. In addition at the two top dose levels there was a slight increase of serum alanine aminotransferase and gamma-glutamyltransferase in males and signs for a minimal regenerative anemia. Increases in total bilirubin and mild increase in hemosiderosis (observed for 1-phenylethanol only) might indicate on a mild hemolysis as possible cause of anemia. Overall, the NOAEL was 75 mg/kg bw/d.

 

Dermal route

No information is available for systemic toxicity after repeated dermal exposure.

 

Inhalation route

 

A number of conventional toxicology studies on rats, mice and rabbits with repeated inhalation exposures are available. Additional data but of deficient quality were reported on inhalation exposure in rhesus monkeys and guinea pigs.

 

Clinical signs indicative of irritation were reported in rats starting at about 400 ppm with a NOEC of 100 ppm (Cragg et al., 1989; Biodynamics, 1986) with similar signs of irritation in mice at 400 ppm (Biodynamics, 1986). Slight body weight depressions in rats started at about 750 ppm (Stott et al.,1999; 2003; NTP, 1992) in studies up to 3 months of duration, while after an exposure period of 2 years (NTP, 1999) such slight effects on body weights were already observed at 250 ppm in rats but not in mice. Mortality was increased after 4 days of exposure in rats at 2400 ppm and in mice at 1200 ppm (Biodynamics, 1986) while after a 2-year exposure there was a decreased survival of male rats at 750 ppm (but not in female rats or mice), most probably related to chronic progressive nephropathy (CPN) (NTP, 1999).

 

The most consistent effect is an increase in liver weight of rats and mice without histopathological alterations by standard procedures in studies with duration up to 3 months (Cragg et al., 1989; Biodynamics, 1986; Stott et al., 1999;2003; Wolf et al., 1956; NTP, 1992, WIL Research Laboratories, 2004; Faber et al, 2006). Such effects were also noted in studies dealing with fertility (cf section 4.1.2.9), e.g. in parental animals of a 1- generation (WIL Research Laboratories, Inc., 2003) and 2 -generation study (WIL Research Laboratories, Inc., 2005)and in a non guideline investigation on female fertility (Andrew et al., 1981; Hardin et al., 1981). Liver changes most probably are related to enzyme induction as has been demonstrated by several authors (Stott et al., 1999; 2003; Elovaara et al., 1985; Toftgard, Nilsen, 1982). This is supported by a proliferation of smooth endoplasmatic reticulum (Elovaara et al., 1985). An increase in kidney weight was also found. A detailed histopathological reevaluation of the kidneys of rats exposed for 3 months in the NTP (1992) study revealed a dose-related increase of the severity of CPN in male rats at 750 and 1000 ppm, but not in females. In addition, an increase in incidence of hyaline droplets was observed at these dose levels in male rats (Hard, 2002). CPN in rats has no specific relevance for humans and liver enzyme induction is not to be considered as a toxicological relevant effect for human risk assessment. The NOEC for all of these findings is 100 ppm and the NOAEC in the most relevant 90 day NTP study (1992) for extrapolation to humans is 1000 ppm (4.74 mg/l).

 

Similar organ-related systemic toxicity was observed after 2 years of exposure (NTP, 1999). In rats a detailed histopathological reexamination again revealed chronic progressive nephropathy at 750 ppm markedly in male and modestly in female rats in all treated groups. There was a high incidence of severe CPN with kidney alterations that may lead to renal failure. Cystic degeneration of the liver was increased in 750 ppm males, but the biological significance in the absence of other hepatotoxic changes is unclear. In mice there was a spectrum of non neoplastic liver changes for both males and females. Histopathological findings related to lung tumor formation will be reported in the section on carcinogenicity. A detailed reevaluation of the lung and liver slices from mice basically confirmed the original NTP findings (Brown, 2000). Hyperplastic changes were also reported for the thyroid in males and females at 750 ppm and for the pituitary in females starting at 250 ppm. In summary, as chronic progressive nephropathy has no toxicological relevance for human risk assessment, the NOAEC for rats was 250 ppm in males and 750 ppm in females if small reductions (5-6%) in body weight (males at 250 ppm and females at all exposure levels) for females are not taken into account. In mice the NOAEC was 75 ppm for males and females based on liver, lung, thyroid and pituitary pathology.

 

Organ-specific toxicity (effects on the nervous system)

In experimental animals ethylbenzene exposure induced various effects on the central nervous system:

Effects on neurotransmitters

Two studies reported modulation of neuronal transmitters at 2000 ppm (Andersson et al., 1981) or 750 ppm (Romanelli et al., 1986; Mutti and Franchini, 1987; Mutti et al., 1988), respectively, over a few days. Furthermore, at 2000 ppm a decrease of prolactin in serum was observed(Andersson et al., 1981). However, the significance of these effects is unclear.

 

Depressive and narcotic effects

Although depressive or narcotic effects have been observed in humans by aromatic solvents in general, the animal data are less consistent showing transient effects for ethylbenzene only at very high acute exposures.

 

In a 90 day oral guideline study specifically designed for the detection of neurotoxic effects dose levels up to 500 mg/kg bw/d did not lead to findings indicative of neurotoxicity in rats (Li et al., 2010).

 

The results of in vitro tests indicate that ethylbenzene may affect the regulatory functions of astrocytes (Naskali et al., 1994;Vaalavirta and Tähti, 1995).

 

It may be suspected that ethylbenzene could lead to lesions in the central nervous system similar to other organic solvents. But no indications for such morphological alterations of the central nervous system have been reported in other animal experiments including the 2-year bioassay with exposures up to 750 ppm (NTP, 1999).But because of the limited reliability of standard H&E staining for detecting neurological disorders this is not sufficient proof for the absence of minor morphological abnormalities.

 

Ototoxicity

Vyskocil et al.(2008) reviewed the literature for ethylbenzene induced effects on the auditory system. In workers, they found no evidence on either ethylbenzene related hearing losses or ototoxic interaction after combined exposure to ethylbenzene and noise. But given the current evidence from animal studies they recommend that ethylbenzene should be considered also as an ototoxic agent for humans.

 

Ethylbenzene leads to ototoxicity in rats. Persistent hearing loss in the mid-frequency range was confirmed in a series of auditory tests in rats (sound-evoked electrical responses, otoacoustic emissions, behavioral auditory tests) corresponding to a concentration dependent death of sensory cells (outer hair cells – OHC, especially in the 3^rdrow) in the upper basal and middle turns of the cochlea. Outer hair cell death determined by histopathology is the most sensitive endpoint for auditory effects (Cappaert et al., 2000; Gagnaire et al., 2007). For death of outer hair cells 200 ppm was a LOEC and the NOEC was calculated to be 114 ppm (95% confidence limit) (Gagnaire et al., 2007). With increasing ethylbenzene concentrations the other endpoints for ototoxicity become affected, too, and OHC death spreads over the frequency range in the cochlea and from row 3 to row 2 and 1 of the outer hair cells. OHC death as confirmed by histopathology indicates that hearing loss is irreversible. This is substantiated by Cappaert et al. (1999) since hearing loss did not change between 1 and 4 weeks post exposure to 800 ppm over 5 days. On the other hand, electrophysiological investigations did not show any further deterioriation of auditory function when exposure to 400 ppm was prolonged from 4 over 8 up to 13 weeks (Gagnaire et al., 2007). Auditory loss remained at the same level following additional 8 weeks of recovery. This might indicate that OHC loss at this concentration was already complete at week 4 and was irreversible.

 

Comparable ototoxic effects were observed in rats that were repeatedly receiving etyhlbenzene via the oral route (Gagnaire and Langlais, 2005), which is in line with the experience gained from other aromatic solvents (e.g., styrene). Since only one concentration of ethylbenzene was examined, (900 mg/kg, 5 d/wk/2 weeks), a N/LOAEL could not be estimated. Other oral tests, also those following OECD standard study designs, did not include specific auditory examinations. By comparison between behavioral and electrophysiological methods Cappaert et al. (1999)concluded that ethylbenzene primarily exerts its effects on the peripheral part of the auditory system.

 

In a comparative study with different aromatic solvents given orally by gavage ethylbenzene belonged to the most potent ototoxicants together with styrene by means of OHC death. The potency was higher than that of toluene and p-xylene. Gagnaire et al. (2007) found that ototoxicity in mixed exposure to xylenes and ethylbenzene mainly depends on the concentration of ethylbenzene and auditory loss was higher in combined exposure than after single exposure to same ethylbenzene concentrations.

 

Experiments with combined exposure to noise and ethylbenzene indicated to a synergistic effect of both (Cappaert et al., 2001). In the other experiment of Fechter et al. (2007) a very high exposure to the solvent mixture used (660 ppm ethylbenzene + 400 ppm toluene) (without noise) did not result in adverse hearing effects in contrast to all the other studies with ethylbenzene, while hearing loss was reported for the combination of this solvent mixture with noise exposure of 93-95 dB. Actually no explanation for this unexpected result could be given. As synergistic effects were also known from mixed exposure to other aromatic solvents, the outcome of this study appears questionable.

 

By comparison with rats, guinea pigs are very insensitive against ethylbenzene-induced ototoxicity (Cappaert et al., 2002). The low sensitivity of guinea pigs was attributed to the low blood concentration of ethylbenzene in comparison to that of rats.

 

The critical question is whether ototoxicity of ethylbenzene in humans is best comparable to that in the rat rather to that seen in the guinea pig. Until the exact position of humans within the inter-species ranking of susceptibility to ethylbenzene-induced ototoxicity is actually known, data from the rat are to be taken as relevant for humans. This assumption is supported by a number of reports on hearing deficits in humans occupational exposed to organic solvents or from people after solvent abuse (for review cf Risk Assessment Reports on toluene and styrene).

 

Ethylbenzene belongs to the most ototoxic aromatic solvents, its potency being comparable to that of styrene but higher than those of toluene or p-xylene. Comparing rat data on the lowest effective concentrations for ethylbenzene and toluene, the risk of ototoxicity is expected to be higher for ethylbenzene.

 

Irreversible damage of auditory function and of sensory cells of the cochlea is a serious health damage. After 13 weeks of exposure minimal effects were still observed at 200 ppm (0.88 mg/l) and the NOEC was extrapolated to 114 ppm (0.5 mg/l). Thus, the classification limit for R48/20 (0.25 mg/l) is formally not attained. Nevertheless, such a classification is proposed taking into account that the experimental ototoxicity of ethylbenzene is comparable to that of styrene and less than that of toluene and that both of these chemicals have been assigned R48/20.

 

With regard to DNEL derivation three aspects have to be critically evaluated:

1.     Influence of exposure duration on NOAEC

2.     Sensitivity of histopathological and (electro)physiological effects

3.     Anatomical/histological differences of target tissues between rats and humans.

 

1. Influence of exposure duration on NOAEC

Ototoxicity leading to an increase of audiometric threshold and specific histopathological alterations with destruction of the outer hair cells in the cochlea (predominantly in row 3) is not a specific effect only of ethylbenzene, but has been described for a variety of other aromatic solvents. In a comparative oral study such histopathological effects were observed for alpha-methylstyrene, trans-beta-methylstyrene, toluene, p-xylene, n‑propyl­benzene, styrene, and allylbenzene apart from ethylbenzene after oral application (Gagnaire and Langlais, 2005). After inhalation exposure qualitatively similar hearing impairments were found by reflex modification audiometry for styrene, toluene and mixed xylenes (Crofton et al., 1994). The inhalation of styrene and toluene again led to similar electrophysiological and histopathological findings (Loquet et al., 1999). Permanent hearing loss as determined by behavioral and electrophysiological methods was also described after inhalation exposure to toluene (Pryor et al., 1984), mixed xylenes, and styrene (Pryor et al., 1987).

 

The weight of evidence obtained from experiments with styrene and other aromatic solvents indicates that ototoxicity is exerted by the lipophilic aromatic parent chemical rather than by a metabolite:

-   Similar ototoxic effects were found for a range of lipophilic organic solvents. As all of these chemicals are biotransformed to different metabolites, indirect evidence is thereby obtained that the parent chemicals themselves most probably lead to ototoxicity

- When rats were exposed to toluene, pre-treatment with phenobarbital prior to toluene inhalation resulted in a marked reduction in blood toluene levels and prevented hearing loss (Pryor et al., 1991) showing induction of metabolism reduces ototoxicity.

-   A comparative study of ototoxicity in rats and guinea pigs showed much higher blood levels of styrene in the rat (i.e. 23 µg/g) leading to ototoxicity, while in the guinea pig the blood levels were about 4-fold lower (i.e. about 5 µg/g) with no evidence of ototoxicity (Lataye et al., 2003). This finding compares well with that of Cappaert et al. (2002) attributing the low sensitivity of guinea pigs for ototoxicity against ethylbenzene to the low blood concentration of the parent chemical in comparison to rats.

-   Inhalation to toluene induced auditory impairment as determined by auditory brainstem response in rats but not in chinchillas under similar exposure conditions. This was explained by species differences in hepatic microsomal metabolism of toluene being highest in chinchillas (Davis et al., 2002)

- No changes in auditory brainstem response were seen in rats treated with phenylglyoxylic acid, a major metabolite of styrene and ethylbenzene, in drinking water over 3 months at doses up to 5000 mg/l, corresponding to 293 mg/kg bw/d (Ladefoged et al., 1998)

- The higher sensitivity of young rats as compared to old ones for ototoxicity was explained by Lataye et al. (2004) by age related increases in styrene metabolism

 

In conclusion, the overall evidence indicates that the mechanism of aromatic solvent induced ototoxicity is very similar for these chemicals, notwithstanding different potencies, and driven by the parent compound and not by their hydrophilic metabolites. A read across approach is therefore indicated to fill specific data gaps for the risk assessment of ethylbenzene

 

There is strong evidence that the maximum of hearing impairment is already reached after one to a few weeks of exposure and that ototoxicity does not increase with prolongation of the exposure period. Campo P. (2001) exposed rats to 1000 ppm styrene (6h/d, 5d/week) for 1, 2, 3, or 4 consecutive weeks. Permanent hearing loss was observed using electrophysiological examinations 6 weeks after the end of each exposure period. An exposure duration of 1 week was enough to obtain the maximal hearing deficit without any further increase by prolongation of exposure. This was confirmed by histopathology of the cochlea carried out 6 weeks post-exposure: hair cell loss was virtually the same after an exposure duration of 1 or 3 weeks.

 

The conclusion that maximal hearing impairment is already reached after a few weeks of exposure can also be indirectly inferred by comparison of the results of The Dow Chemical Company (1992) and Maekitie et al. (2003). The Dow Chemical Company (1992) exposed male Fisher-344 rats (6h/d, 5d/week) to 0, 50, 200 and 800 ppm styrene over 13 weeks. Effects on the auditory system were determined by electrophysiology and histopathology of the cochlea a few days after the end of exposure. Clear effects were noted at an exposure of 800 ppm and the NOAEC was 200 ppm. This compares well to the NOAEC of 300 ppm determined in male Wistar rats by Maekitie et al. (2003)after an exposure to 0, 100, 300 and 600 ppm (12h/d, 5d/week) over only 4 weeks.

 

The conclusion that solvent induced ototoxicity already appears after a relatively short exposure duration and that continued exposure does not enhance the intensity of the response or reduces the NOAEC is also supported by studies with toluene. In a review Johnson and Nylen (1995) described for toluene that a time-integrated concentration between 12000 and 16000 ppm x h/d over 3 days was sufficient to cause loss of auditory sensitivity, while 6000 ppm x h/d over 18 month failed to produce ototoxic effects. Pryor et al. (1984) showed that a 2 week exposure to 1000 ppm toluene (14h/d, 7d/week) produced ototoxicity in Fischer rats while no effects were seen for a similar exposure schedule over 16 weeks to 400 and 700 ppm. Even 3 days at 1500 ppm (14h/d) or at 2000 ppm (8h/d) were sufficient to induce hearing loss. Nylen et al. (1987) demonstrated that the ototoxicity of toluene is governed by intensity of exposure and not by duration or cumulative exposure. Impairment of auditory function as determined electrophysiologically was found in male Sprague Dawley rats after exposure to 1000 ppm (22h/d, 7d/week) over 1 month corresponding to 0.62 million ppm x h. On the other hand, no effects were found after a cumulative exposure of 2.46 million ppm x h achieved by a shorter weekly exposure regime to 1000 ppm (6h/d, 5d/week) over 19 month.

 

Direct evidence that maximal hearing impairment will already be reached after a few weeks of exposure is also obtained by the data of Gagnaire et al. (2007) with ethylbenzene itself. Hearing deficits recorded electrophysiologically 4, 8, and 13 weeks after start of exposure (6h/d, 6d/week) and after additional 8 weeks of exposure free observation were all essentially the same: there was no increase of hearing loss over time and the NOAEC of 200 ppm did not change. The same applied for the two different mixed xylenes tested, containing either 10% or 20% of ethylbenzene.

 

In summary, an exacerbation of hearing deficits is not to be expected by prolongation of exposure beyond a few weeks or from 13 weeks to life time.

 

2. Sensitivity of histopathological and (electro)physiological effects

In the overall assessment it has also be taken into consideration that the NOAEC for ototoxicity as defined by auditory dysfunction is clearly higher than that defined by histopathological effects on the outer hair cells of the cochlea. Numerous investigations have shown that audiometric hearing deficits occur at higher exposure concentrations than (small) losses of hair cells in the outer row 3 of the cochlea. This was described by Gagnaire et al. (2007) for ethylbenzene and two different mixed xylenes. The NOAECs/LOAECs were found at the following concentration: ethylbenzene: auditory threshold - NOAEC 200 ppm; histopathology - LOAEC 200 ppm; mixed xylene (1): auditory threshold - NOAEC 500 ppm; histopathology - LOAEC 250 ppm; mixed xylene (2): auditory threshold - NOAEC 1000 ppm; histopathology - NOAEC 500 ppm.

 

Similar findings were reported for styrene by Loquet et al.(1999), Lataye et al. (2005), Pouyatos et al. (2002), or Lataye et al.(2001).In this respect the findings of Lataye et al. (2001) are important. After exposure to styrene at 1000 and 1500 ppm there was a clear cell loss in the medium spiral ganglion, but not at 750 ppm corresponding better to the dose response relationship of hearing loss (by electrophysiology) than the outer hair cell loss in the cochlea. Thus, the functional results are in better agreement with the morphological results at the level of the spiral ganglion than with those obtained at the level of the cochlea.

 

The inconsistency in the dose response relationship of the degenerative process of hair cells along the cochlea on the one hand with electrophysiologically measured changes of the auditory threshold on the other hand can be explained by the anatomical situation. To begin with, the auditory message comes mainly from the inner hair cells which are much less prone to damage by organic solvents than the outer hair cells, especially those in row 3. Secondly, the functional results of hearing loss are in better agreement with histopathological changes in the spiral ganglion rather than with those at the level of the cochlea. In this respect Lataye et al. (2001) point to an investigation of Prosen et al. (1990) who showed that a massive loss of outer hair cells (up to 50% in the 30% apical region of the cochlea) did not cause hearing loss at any frequency. They conclude that the functional role played by the apical outer hair cells appears to be secondary in the rat. Furthermore after oral exposure of rats to styrene Chen et al. (2008) found that a loss of outer hair cells of <33% did not result in a significant shift of hearing threshold.

 

Thus, taking very small losses of outer hair cells in row 3 as the decisive endpoint is a very conservative approach for risk assessment based upon hearing impairment.

 

3. Anatomical/histological differences of target tissues between rats and humans.

The mechanism was clarified for styrene by Campo P. (1999), Loquet et al. (1999), and Campo P. et al. (2001): Styrene, transported by blood coming from the stria vascularis or the spiral prominence, diffuses through the outer sulcus to reach the lipid-rich Hensen’s cells. These cells are in close connection with the Deiters cells that are directly located under the outer hair cells. Thus, the target cells are reached by diffusion of styrene. This explains why hair cells are lost in a sequence from the outer row 3 to row 1 as diffusion continuous and why the inner hair cell are the least sensitive. Specifically, the involvement of Hensen’s and Deiters cells was supported by histopathology of semi-thick sections of the cochlea (Campo et al., 2001) and Chen et al. (2007) demonstrated that Deiters cells are an especially vulnerable target of styrene. The latter authors further reported that the styrene concentrations in the cochlea varied along with the basilar membrane with the lowest level in the basal turn being consistent with the lowest styrene induced threshold shift and hair cell loss in this region.

 

The mode of action for hearing loss induced by styrene is well-defined and the weight of evidence indicates that it also applies to other aromatic solvents including ethylbenzene. As shown above ototoxicity is governed by direct impact of the (unmetabolised) parent compound on the hair cells of the cochlea. Passage to these target cells occurs via diffusion of the solvent from blood through Hensen’s and Deiters cells. Taking into account the identical target cells (outer hair cells, Hensen’s cells, Deiters cells) and the identical structure of the target organ (cochlea) and even its blood supply, the toxicodynamics for ototoxicity caused by aromatic solvents are very similar between species. This also applies to the comparison between humans and rats if as a conservative assumption humans are considered to be of comparable sensitivity as rats.

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

The repeated exposure toxicity of ethylbenzene has been evaluated in animals in subchronic and chronic inhalation studies, subchronic oral toxicity studies and numerous specialized investigations. Overall, ethylbenzene poses a moderate repeated exposure toxicity hazard with consistent targeted effects to the liver, kidney and hearing.

Repeated dose toxicity (Oral):

Changes in hematology, indicative of a mild regenerative anemia, and clinical chemistry parameters, indicative of hepatic microsomal enzyme induction, decreases in prothrombin time, mild alimentary effects and kidney (males only) and liver pathology were observed in rats that received gavage doses of > 250 mg/kg bwt/day ethylbenzene for 90 days.

Repeated dose toxicity (Dermal):

No data

 

Repeated dose toxicity (Inhalation):

90 day inhalation study in rats concluded ototoxic effects at> 200 ppm. The study NOAEC was calculated to be 114 ppm (500 mg/m3).

Value used for CSA (via oral route - systemic effects):

(NOAEL: 75 mg/kg bw/day)

Value used for CSA (inhalation- systemic effects):

(NOAEC: 500 mg/m³)

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Changes in hematology, indicative of a mild regenerative anemia, and clinical chemistry parameters, indicative of hepatic microsomal enzyme induction, decreases in prothrombin time, mild alimentary effects and kidney (males only) and liver pathology were observed in rats that received gavage doses of > 250 mg/kg bwt/day ethylbenzene for 90 days.

Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
90 day inhalation study in rats concluded ototoxic effects at > 200 ppm.

Justification for classification or non-classification

Oral: Based on the results of the subchronic gavage study with rats (observed NOAEL = 75 mg/kg bw/d, which is above the cut-off value of 50 mg/kg bw/day established for the 90-day study), classification is not warranted according to Directive 67/548/EEC.

 

According to EU CLP (Regulation (EC) No. 1272/2008) and UN GHS the NOAEL of 75 mg/kg bw/d falls within the range of 10-100 mg/kg bw/d for STOT-RE Cat. 2 classification. But the severity of the effects observed at the next dose level (250 mg/kg bw/d) does not justify classification according to section 3.9.2.8. Thus, a classification according to EU CLP (Regulation (EC) No. 1272/2008) is not warranted by this study.

 

Ototoxicity was not investigated by the above mentioned oral gavage study. Gagnaire and Langlais (2005) observed ototoxicity in rats at a single high dose level of 900 mg/kg bw/d over two weeks. This study is not sufficient for classification. But the inhalative NOAEC (500 mg/m³) may be extrapolated to an oral dose:

oral absorption rat: 84%

inhalative absorption rat: 45%

respiratory volume rat (6h): 0.29 m³/kg.

Thus, the NOAEC of 500 mg/m³ corresponds to

           500 x 0.29 x 0.45 : 0.84 = 78 mg/kg bw/d.

 

Thereby a classificationaccording to Directive 67/548/EEC is not warranted.

But according to EU CLP (Regulation (EC) No. 1272/2008) and UN GHS STOT-RE Cat 2 is justified: H 373: May cause damage to the auditory system by prolonged or repeated oral exposure.

 

Dermal: No studies with repeated dermal exposure are available. Taking into account the dermal absorption of 4% (see DNEL derivation) a classification according to Directive 67/548/EEC,EU CLP (Regulation (EC) No. 1272/2008) and UN GHS is not warranted based on the same calculation as above:

           500 x 0.29 x 0.45 : 0.04 = 1630 mg/kg bw/d.

 

Inhalation: Irreversible damage of auditory function and of sensory cells of the cochlea is a serious health concern. After 13 weeks of exposure minimal effects were still observed at 200 ppm (0.88 mg/l) and the NOEC was extrapolated to 114 ppm (0.5 mg/l). Thus, according to Directive 67/548/EEC the classification limit for R48/20 (0.25 mg/l) is formally not attained. Nevertheless, such a classification is proposed taking into account that the experimental ototoxicity of ethylbenzene is comparable to that of styrene and the NOAEC is less than that of toluene and that both of these chemicals have been assigned R48/20.

 

On the other hand, according to EU CLP (Regulation (EC) No. 1272/2008) and UN GHS the NOAEC of 0.5 mg/l is within the classification limit of 0.2-1 mg/l/6h/d for STOT-RE Cat. 2 leading to a classification with H 373: causes damage to the auditory system through prolonged or repeated inhalative exposure.

 

In summary, the following classifications are justified for repeated dose toxicity:

 

Directive 67/548/EEC: R48/20: danger of serious damage to health by prolonged exposure through inhalation. A harmonized classification exists for ethylbenzene, however this hazard category is not included. Recommendation is to add R48/20. 

EU CLP (Regulation (EC) No. 1272/2008): A harmonized classification exists for ethylbenzene, however this hazard category is not included. Recommendation is to add: STOT-RE Cat 2, H 373: causes damage to the auditory system through prolonged or repeated oral or inhalative exposure and also recommended for UN GHS. After reviewing this information, the Committee for Risk Assessment concluded that ethylbenzene had a potential to cause damage to organs (hearing) through prolonged or repeated exposure (RAC, 2012a).

RAC (2012) Opinion proposing harmonised classification and labelling at EU level of ethylbenzene. ECHA/RAC/CLH-O-0000001542-81-03/F. Committee for Risk Assessment, adopted 5 June 2012