Registration Dossier

Diss Factsheets

Administrative data

Description of key information

In animal studies xylene isomers (including mixed xylene) exhibit low acute toxicity by oral and dermal routes with the reported LD50 values all exceeding 2000 mg/kg bw. Mixed xylene is considered harmful by inhalation.
In humans critical effects of xylenes are irritation and CNS effects, with the overall NOAEC inhalation for the latter effect being 300 mg/m3.

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records
Reference
Endpoint:
acute toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP status not known, guideline study, published in peer reviewed literature, no restrictions, fully adequate for assessment.
Qualifier:
equivalent or similar to guideline
Guideline:
EU Method B.1 (Acute Toxicity (Oral))
GLP compliance:
no
Test type:
standard acute method
Limit test:
no
Species:
rat
Strain:
other: F344/N
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: Charles River Breeding Laboratories (Kingston, NY, USA)
- Age at study initiation: 7 weeks
- Housing: 5 per sex /cage in polycarbonate cages
- Diet: Purina Lab Chow available ad libitum
- Water: ad libitum
- Acclimation period: 18 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22° ± 1°C
- Humidity: 40 - 60%
- Air changes: 15 air changes/hour
- Photoperiod: 12 hour dark/ 12 hour light

IN-LIFE DATES: From: 5 March 1979 To: 19 March 1979

Route of administration:
oral: gavage
Vehicle:
corn oil
Details on oral exposure:
Oral (gavage): 500, 1000, 2000, 4000 or 6000 mg/kg xylenes (mixed) in corn oil; dose volume 8 mL/kg
Preparation: Weighed portions of xylenes (mixed) were placed in a graduated cylinder and mixed with corn oil.
Doses:
Single dose
No. of animals per sex per dose:
5
Control animals:
no
Details on study design:
Groups of five rats of each sex were administered a single dose of 500, 1,000, 2,000, 4,000, or 6,000 mg/kg xylenes in corn oil by gavage. The animals were observed twice daily for 14 days and were killed on day 16. A necropsy was not performed.
Statistics:
LD50 calculated by Spearman-Karber procedure.
Sex:
male
Dose descriptor:
LD50
Effect level:
3 523 mg/kg bw
95% CL:
2 707 - 4 587
Sex:
female
Dose descriptor:
LD50
Effect level:
> 4 000 mg/kg bw
Mortality:
All the rats that received 6,000 mg/kg and 3 of 5 males that received 4,000 mg/kg died within 48 hours of dosing.
Clinical signs:
other: other: Lack of coordination, prostration, loss of hindleg movement, and hunched posture were detected within 24 hours of dosing in male and female rats that received 4,000 or 6,000 mg/kg. Male and female rats that received 2,000 mg/kg had rough coats. N
Interpretation of results:
not classified
Remarks:
Criteria used for interpretation of results: EU
Conclusions:
The oral LD50 in rats was 3523 mg/kg/bw for males and greater than 4000 mg/kg/bw for females.
Executive summary:

In a single-administration study, groups of five F344/N rats of each sex received 500, 1,000, 2,000, 4,000, or 6,000 mg/kg. Administration of mixed xylenes caused deaths at 6,000 mg/kg in each sex and at 4,000 mg/kg in males. Clinical signs observed within 24 hours of dosing at 4,000 mg/kg included prostration, muscular incoordination, and loss of hind limb movement; these effects continued through the second week of observation. The LD50 was 3523 mg/kg/bw for males and greater than 4000 mg/kg/bw for females.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
LD50
Value:
3 523 mg/kg bw
Quality of whole database:
Multiple studies conducted in rats and mice consistently demonstrate that the oral LD50 for xylene isomers (including mixed xylene) exceeds 2000 mg/kg bw.

Acute toxicity: via inhalation route

Link to relevant study records
Reference
Endpoint:
acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant, guideline study, animal experimental study, no restrictions, fully adequate for assessment.
Qualifier:
equivalent or similar to guideline
Guideline:
EPA OPP 81-3 (Acute inhalation toxicity)
GLP compliance:
yes (incl. QA statement)
Test type:
standard acute method
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Strain: Crl:CD(SD)BR
- Source: Charles River Laboratories, Margate, Kent UK
- Age at study initiation: 6-8 weeks
- Weight at study initiation: 200-350g
- Housing: by sex, 5 per polypropylene cage with grid flooring
- Diet: SQC Rat & Mouse Maintenance Diet No. 1 ad libitum except during exposure
- Water: Mains water ad libitum except during exposure
- Acclimation period: minimum 3 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22±3°C
- Humidity: 40-70%
- Air changes: 15 per hr
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From: 13 January 1986 To: 12 March 1986
Route of administration:
inhalation: vapour
Type of inhalation exposure:
head only
Vehicle:
other: air
Details on inhalation exposure:
A heated ‘J’ tube with an in-line filter was used to produce the atmosphere within the cylindrical Perspex chamber of approximately 10 L internal volume. The p-xylene was metered to the generator using a flowmeter and heated by passage through a borosilicate glass tube located inside a furnace whose temperature was regulated with a variable resistor. The hot air then passed into the glass ‘J’ tube packed with glass beads. The p-xylene was slowly pumped into the ‘J’ tube where it vaporised and the resulting vapour cooled prior to passage through the in-line filter to remove any aerosol before passing into the chamber. Satisfactory control over the chamber atmospheres was achieved.
The exposure chamber temperature and humidity were 14-21°C and 30-54% respectively. The diluents air flow rate was 14-17 litres/minute. The oxygen concentration was 20-22%.
Analytical verification of test atmosphere concentrations:
yes
Remarks:
Twice hourly sampling through a Miran 1A infra-red gas analyser.
Duration of exposure:
4 h
Concentrations:
Nominal concentrations: 0, 3056, 4200, 5097, 5897, 7881 ppm
Measured concentrations: 0, 2502, 3754, 4349, 5003, 7553 ppm
7553 ppm is 75% of the lower explosive limit
No. of animals per sex per dose:
5
Control animals:
yes
Details on study design:
The day of exposure was followed by a 14 day observation period.
Statistics:
Mean and standard deviation were calculated where appropriate. The median lethal concentration (LC50) and the 95% confidence limits were calculated using a probit analysis method.
Sex:
male/female
Dose descriptor:
LC50
Effect level:
6 247 ppm
Exp. duration:
4 h
Remarks on result:
other: 27124 mg/m3
Sex:
male
Dose descriptor:
LC50
Effect level:
5 922 ppm
Exp. duration:
4 h
Remarks on result:
other: 25713 mg/m3
Sex:
female
Dose descriptor:
LC50
Effect level:
6 580 ppm
Exp. duration:
4 h
Remarks on result:
other: 28570 mg/m3
Mortality:
60% at 5003 and 7553 ppm mostly during exposure. No mortality at lower concentrations.
Clinical signs:
other: Body tremors suggestive of CNS involvement were seen at all concentrations during and after exposure, on the day of exposure. Mydriasis and respiratory difficulties including rapid respiration observed in majority of animals surviving 4349 ppm and higher.
Body weight:
No effect of p-xylene.
Gross pathology:
Animals that died showed signs of circulatory failure. There were no treatment-related changes in survivors at termination suggestive of irreversible or delayed target organ toxicity.
Interpretation of results:
not classified
Remarks:
Criteria used for interpretation of results: EU
Conclusions:
Groups of male and female rats were exposed (head only) to measured concentrations p-xylene vapour for 4 hours followed by a 14 day observation period. The LC50 was 6247 ppm (27124 mg/m3. 27.1 mg/L).
Executive summary:

Groups of male and female rats were exposed (head only) to measured concentrations p-xylene vapour for 4 hours followed by a 14 day observation period. The LC50 was 6247 ppm (27124 mg/m3, 27.1 mg/L) Clinical observations including body tremors suggestive of CNS involvement were seen at all concentrations during and after exposure, on the day of exposure.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LC50
Value:
27 124 mg/m³ air
Quality of whole database:
Multiple studies conducted in rats and mice consistently demonstrate that the inhalation LC50 for xylene isomers (including mixed xylene) exceeds 20,000 mg/m3.

Acute toxicity: via dermal route

Link to relevant study records
Reference
Endpoint:
acute toxicity: dermal
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-GLP, near guideline study, published in peer reviewed literature, limitations in design and/or reporting but otherwise adequate for assessment.
Qualifier:
no guideline followed
Principles of method if other than guideline:
Single dermal dose under occlusion followed by observation for 14 days.
GLP compliance:
no
Test type:
standard acute method
Limit test:
no
Species:
rabbit
Strain:
New Zealand White
Sex:
male
Details on test animals or test system and environmental conditions:
TEST ANIMALS
Weight at study initiation: 2.5-3.5 kg


Type of coverage:
occlusive
Vehicle:
unchanged (no vehicle)
Details on dermal exposure:
Fur removed from the entire trunk by clipping and the dose retained beneath an impervious plastic film for 24 hours, after which the film was removed.
Duration of exposure:
24 hours
Doses:
Not reported
No. of animals per sex per dose:
4
Control animals:
not specified
Details on study design:
Duration of observation period following administration: 14 days
Statistics:
Dermal LD50 (and its fiducial range) estimated. Methods used are not detailed (probit analysis assumed).
Sex:
male
Dose descriptor:
LD50
Effect level:
12 126 mg/kg bw
Remarks on result:
other: 14.1 mL/kg bw adjusted for density of 0.86
Clinical signs:
other: other:
Interpretation of results:
not classified
Remarks:
Criteria used for interpretation of results: EU
Conclusions:
The acute dermal LD50 of m-xylene in the male New Zealand White rabbit was 12126 mg/kg.
Executive summary:

The acute dermal LD50 of m-xylene in the male New Zealand White rabbit was 14.1 mL/kg bodyweight, equivalent to 12126 mg/kg.

Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
LD50
Value:
12 126 mg/kg bw
Quality of whole database:
The available data indicate that the dermal LD50 in rabbits exceeds 2000 mg/kg bw.

Additional information

The multi-constituent substances covered by this registration comprises of individual xylene isomers (m-xylene, o-xylene, p-xylene) and ethylbenzene (>10% - <20%). The following information is available to characterise their acute health hazards.

Acute toxicity: oral

Non-human information

Acute oral data is available for mixed xylene, xylene isomers and ethylbenzene.

The acute oral LD50 of mixed xylene (containing 17% ethylbenzene) in rats is 3523 mg/kg. This information is derived from what is considered to be the key study (NTP, 1986) as this is the most recent study with the lowest reported LD50 value.

Xylene is of low toxicity via the oral route. The LD50 values for xylene isomers (including mixed xylene) range from 3523 to 8400 mg/kg (NTP, 1986; Hine & Zuidema, 1970; Wolf et al., 1956; Smyth et al., 1962).

The acute oral toxicity of ethylbenzene is low with LD values above 2000 mg/kg. An oral LD50 of 3500 mg/kg was determined for rats (male/female) (RAR 2008).

Human information

No relevant information sourced for mixed xylene, xylene or ethylbenzene.

Acute toxicity: inhalation

Non-human information

An LC50 value of 27,571 mg/ m3 was obtained for male rats exposed to mixed xylene (composition undefined) for 4 hours (Hine, 1970).

Considering xylene isomers, an LC50 of 27,124 mg/m3 has been derived for p-xylene from what is considered to be the key study (HLE, 1986). This study provides the lowest reported LC50 value for a guideline exposure period of 4 hours. This is a GLP compliant study and the most recently conducted. The LC50 value of 27,124 mg/m3 is a combined value for males and females; the LC50 for males was 25,713 mg/m3 and for females, 28,570 mg/m3.

Ethylbenzene is harmful by inhalation, with the LC50 in rats reported as 17,600 mg/m3after the guideline exposure period of 4 hours (RAR, 2008).

Human information

Mild eye and upper tract respiratory tract irritation has been reported (see 5.3 below).

Neurological and physiological symptoms have been reported in workers exposed to xylene, but this is mainly resulting from exposure to solvent mixtures and therefore difficult to attribute directly to xylene. The lowest NOAEC reported for CNS effects which is considered reliable is for p-xylene at 70 ppm (Anshelm Olson, 1985).This value is consistent both with the SCOEL review and reviews (e. g. UK HSC, 2001) supporting the existing IOELV for the xylene isomers.

There are no specific human data for ethyl benzene (RAR, 2008).

Acute toxicity: dermal

Non-human information

The data for mixed xylene (composition undefined) supports the conclusion that the LD50 would be >2000 mg/kg bw, with an LD50 of >4600 mg/kg bw reported (Hine & Zuidema, 1970).

A dermal LD50 in rabbits of 12,126 mg/kg is derived for m-xylene from what is considered to be the key study (Smyth, 1962) as the lowest reported LD50 value.

The acute dermal toxicity of ethylbenzene has been reported as being tested with rabbits and revealed a dermal LD50 of 15500 mg/kg (RAR, 2008).

Human information

No human information is available.


Justification for selection of acute toxicity – oral endpoint
For mixed xylene an acute oral LD50 in rats of 3,523 mg/kg is derived from NTP (1986). This is the most recent investigation available and provides the lowest oral LD50 value for xylene isomers (including mixed xylene). The oral LD50 of ethyl benzene in rats is 3500 mg/kg (RAR, 2008).

Justification for selection of acute toxicity – inhalation endpoint
For p-xylene an acute inhalation LC50 in rats of 27,124 mg/m3 is available (HLE, 1986). This is the most recent investigation available and provides the lowest inhalation LC50 value for a 4-hr exposure period. For mixed xylene, an LC50 of 27,571 mg/m3 has been reported (Hine and Zuidema, 1970). A 4 hr LC50 of 17,600 mg/m3 has been reported for ethyl benzene in rats (RAR, 2008).
Note: Although xylene isomers (including mixed xylenes) are classified H332 - Harmful if inhaled according to the CLP regulation, the rationale for this is not clear since the available LC50 values are clearly greater than 20,000 mg/m3. Ethylbenzene is also classified H332 according to the CLP regulation.

Justification for selection of acute toxicity – dermal endpoint
A dermal LD50 in rabbits of 12,126 mg/kg bw is derived for m-xylene from Smyth et al. (1962) while an LD50 of >4200 mg/kg bw is reported for mixed xylene (Hine and Zuidema, 1970). The dermal LD50 of ethyl benzene in rabbits is 15,500 mg/kg bw (RAR, 2008).
Note: Although xylene isomers (including mixed xylene) are classified H312 - Harmful in contact with skin according to the CLP regulation, the rationale for this is not clear since the LD50 is clearly above 2,000 mg/kg bw.

Substance selection for risk characterization:  

The approach developed by the LOA Exposure Working Group on the selection of constituents for use in human health exposure assessments was implemented for this Reaction Mass substance. The primary constituents used are ethylbenzene and xylenes. A full description of this approach is available in Section 13 (”Selection of constituents for HH exposure” in section 13.2). 

Justification for classification or non-classification

Although xylene (individual and pure mixed isomers) is classified as Acute Tox Cat 4 H332 Harmful if inhaled under CLP,the rationale for this is not clear since the LC50 is clearly above 20,000 mg/m3 and classification would appear not to be justified. 

No classification is warranted for acute toxicity via oral route under CLP.

Although xylene (individual and pure mixed isomers) is currently classified as Acute Tox Cat 4 H312 Harmful in contact with skin,the rationale for this is not clear since the LD50 is clearly above 2,000 mg/kg bw and classification would appear not to be justified. 

Aspiration is a known hazard of hydrocarbons and classification is based on physical characteristics. The kinematic viscosity of xylenes is considered to be below the cut off values for CLP of 20.5 mm2, and therefore classification as Aspiration Tox Cat 1 H304 May be fatal if swallowed and enters airways is warranted under CLP.

Ethylbenzene

Oral LD50 for rats: 3500 mg/kg bw. In accordance with EU CLP (Regulation (EC) No. 1272/2008), classification is not required for acute oral toxicity based on the available data.

Dermal LD50 for rabbits: 15.4 g/kg bw. No classification in accordance with EU CLP (Regulation (EC) No. 1272/2008) and UN GHS.

Inhalation LC50 for rats: 17.6 mg/l/4h (approx. 4000 ppmV). Acute Toxicity Cat. 4, H332, harmful if inhaled in accordance with EU CLP (Regulation (EC) No. 1272/2008).

Lung toxicity after oral exposure; There is indication from animal experiments that pulmonary injury resulting in chemical pneumonitis might be the principal cause of the deaths observed after oral administration of ethylbenzene to rats because necropsy after oral administration revealed hyperaemia and haemorrhage of the lungs. Therefore, aspiration of even a small amount of ethylbenzene may cause severe lung injury. And due to its low viscosity and surface tension ethylbenzene would spread over a large area of pulmonary tissue, causing oedema and haemorrhage.

Therefore, the following classification is proposed: 

Aspiration Cat 1(b) based on animal and physico-chemical data; H304; may be fatal if swallowed and enters the airways in accordance to EU CLP (Regulation (EC) No. 1272/2008).

After reviewing this information, the Committee for Risk Assessment concluded that ethylbenzene may be fatal if swallowed and enters the airways (RAC, 2012 a).

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.