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EC number: 292-637-8 | CAS number: 90641-13-7 A complex combination of hydrocarbons produced by the distillation of the products from a steam cracking process thereafter treated with hydrogen in the presence of a catalyst. It consists predominantly of aromatic hydrocarbons having carbon numbers in the range of C9 through C10 and boiling in the range of approximately 140°C to 200°C (284°F to 392°F).
Repeated dose toxicity data are not available for the high benzene naphtha streams. However, there are substantial data on the repeated dose toxicity of a number of marker constituents present in some streams: benzene, toluene, DCPD, cyclohexane, xylene, and ethylbenzene. A number of the marker constituents demonstrate significant target organ toxicity, therefore they drive the mammalian toxicity effects in the streams (benzene and styrene - when present at 1%; toluene/ ethylbenzene - when present at 10%; n-hexane - when present at 5%).
Groups of 10 or 15 rats/sex were administered 0, 25, 50, 100, 200, 400 or 600 mg/kg benzene in corn oil by gavage, 5 days/ week for 17 weeks. Five rats/sex were killed on days 0 and 60 from the 0, 200, and 600 mg/kg groups, remaining surviving animals were killed on day 120. Clinical observations, bodyweights, food consumption, haematological analyses and histopathological examinations were performed. No compound-related deaths occurred. Final mean body weights (relative to those of the vehicle controls) were depressed 14%-22% for male and female rats that received ≥200 mg/kg benzene. A dose-related leukopenia and lymphocytopenia was observed in males at ≥200 mg/kg and in females at ≥25 mg/kg. In the spleen, lymphoid depletion of B-cells was observed in both sexes at ≥200 mg/kg benzene and increased extramedullary haematopoiesis was observed 600 mg/kg.
NOAEL for males was 100 mg/kg/day. LOAEL for males was 200 mg/kg and for females was 25 mg/kg/day.
No exposure-related mortality or effects on mean body weight and clinical signs were seen. Female rats of the 30 ppm dose group showed lower thyroid weight on day 14 only. At 300 ppm statistically significant decreases in WBC counts were seen in males on day 14 and females on day 91; statistically significant decreases in percent lymphocytes were noted in both males and females on days 14, 28, 56 and 9 (no further detail provided). At this same dose level decreased femoral marrow cellularity was seen on day 7 only.
A subchronic inhalation toxicity study of benzene was conducted in Sprague-Dawley rats. Four groups of animals consisting of 50 rats/sex each were exposed to concentrations of 0, 1, 10, 30, and 300 ppm (0, 3.2, 9.6, 960 mg/m3) benzene vapour, 6 h/day, 5 days/week, for 13 weeks. Ten rats/sex in each group were sacrificed after 7, 14, 28, 56, and 91 days of treatment. Criteria used to evaluate exposure-related effects included behaviour, bodyweights, organ weights, clinical pathology, gross pathology, and histopathology.
No consistent exposure-related trends were seen in the clinical observations and bodyweight data. Exposure-related clinical pathology changes were seen in the high-level (300 ppm) animals. Decreased lymphocyte counts and a relative increase in neutrophil percentages were the only exposure-related clinical pathology alterations. The only exposure-related lesion consisted of slightly decreased femoral marrow cellularity in the animals exposed to 300 ppm.
The NOAEC for toxicity at 28 and 90 days was 30 ppm (96 mg/m3) for both male and female rats.
The available data on the marker consituents xylene and DCPD do not reveal any specific target organ toxicity of a severity that would warrant classification. Therefore, no classification or labelling is warranted for streams which only contain these components.
Other specific components which have been identified as present in some streams are benzene and toluene. These are all identified as producing serious target organ toxicity following repeated oral, dermal or inhalation exposures in animals and man:
Benzene (Classification: STOT-RE Category 1, H372): After repeated dose exposure via oral or inhalation routes, benzene causes adverse effects on the haematopoietic system of animals and man. The oral LOAEL was 25 mg/kg bw/day for male and female mice (NTP, 1986) and the inhalation LOAEC for haematotoxicity in mice is 10 ppm (32 mg/m3) (Ward et al, 1985). In humans, a recent study of petroleum distribution workers exposed to relatively low levels of benzene (Schnatter et al., 2012) reported associations between myelodysplastic syndrome (MDS) and benzene exposure, however while the association appeared to be reasonably robust, it was difficult to ascribe a precise dose/response relationship. For humans, therefore, a NOAEC of 3.5 ppm (11.2 mg/m3) is obtained based on the 95% LCL for the threshold level of neutrophils, the most sensitive endpoint reported by Schnatter et al (2010).
Toluene (Classification: STOT-RE Category 2, H373): Toluene exposure can produce central nervous system pathology in animals after high oral doses. Repeated inhalation exposure can produce ototoxicity in the rat and high concentrations are associated with local toxicity (nasal erosion). In humans neuropsychological effects and disturbances of auditory function and colour vision have been reported, particularly when exposures are not well controlled and/or associated with noisy environments. The NOAEC for subchronic oral toxicity in rats is 625 mg/kg/day based on neuropathology (NTP, 1990). The NOAEC for inhalation toxicity in the rat is 300 ppm (1131 mg/m3) based on effects on body weight, mortality and adverse local effects (nasal erosion) (Gibson and Hardisty, 1983). The NOAEC for neuropsychological effects, auditory dysfunction and disturbances of colour vision in humans is 26 ppm (98 mg/m3) (Seeber et al, 2004); Schaper et al, 2003, 2004).
Ethylbenzene (Classification: STOT-RE Category 2, H373): Ethylbenzene is classified in Annex VI of the CLP regulation as being harmful to hearing organs following repeated dose exposure.
Styrene (Classification: STOT-RE Category 2, H373): Styrene is classified in Annex VI of the CLP regulation as being harmful to hearing organs following repeated dose exposure.
n-hexane (Classification: STOT-RE Category 2, H373): n-hexane is classified in Annex VI of the CLP regulation as being harmful following repeated dose exposure.
Spencer PS and Schaumburg HH (1985). Organic solvent neurotoxicity - facts and research needs. Scand J Work Environ Health 11, 53 -60.
Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
Several of the marker substances present are associated with serious target organ effects e.g. benzene, toluene. Results obtained for the key component benzene are considered indicative of the overall potential hazard of these streams after repeated exposure.
Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:
Several of the marker substances present are associated with serious target organ effects e.g. benzene, toluene. Results obtained for the key component benzene are considered indicative of the overall potential hazard of these streams after repeated exposure. Human data show haematological changes in neutraphil counts with a NOAEC of 3.5 ppm (11.2 mg/m3).
Justification for selection of repeated dose toxicity dermal - systemic effects endpoint:
Sub-acute data available for representative streams indicate no potential to affect health following repeated skin contact, however several of the marker substances present are associated with serious target organ effects e.g. benzene, toluene. Results obtained for the key component benzene are considered indicative of the overall potential hazard of these streams after repeated exposure.
Repeated dose toxicity: via oral route - systemic effects (target organ) cardiovascular / hematological: bone marrow
Repeated dose toxicity: inhalation - systemic effects (target organ) cardiovascular / hematological: bone marrow
Repeated dose toxicity: dermal - systemic effects (target organ) cardiovascular / hematological: bone marrow
There are sufficient data available to conclude that the high benzene naphtha streams, which contain less than 1% benzene / styrene, less than 5% n-hexane, and less than 10% toluene/ethylbenzene, do not require classification for this endpoint.
Streams which contain ≥1% but less than 10% benzene or styrene will require to be classified as follows: Cat 2, H373 according to Reg (EC) 1272/2008; streams containing ≥10% benzene or styrene should be classified Cat 1, H372 according to Reg (EC) 1272/2008.
Streams which contain ≥5% n-hexane should be classified as Cat 2, H373 according to Reg (EC) 1272/2008.
Streams which contain ≥10% toluene/ ethylbenzene should be classified as Cat 2, H373 according to Reg (EC) 1272/2008.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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