p-xylene

Endpoint summary

Description of key information

In animal studies xylenes exhibit low acute toxicity by oral (LD50 3,523 mg/kg), inhalation (4h LC50 27,124 mg/m³) and dermal (LD50 12,126 mg/kg) routes.

In humans critical effects are irritation and CNS effects.

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: 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. No clini

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 xylenes) 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 xylenes) 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

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

Acute toxicity is generally characterised by clinical signs of central nervous system depression including comatose condition, prostration and lack of co-ordination.

The acute toxicity of mixed xylenes and the xylene isomers was reviewed and reported by ATSDR (2007). Some additional relevant data from proprietary studies has been sourced.

Acute toxicity: oral

Non-human information

Xylene is of low toxicity via the oral route. The LD50 values range from 3523 to 8640 mg/kg (NTP, 1986; Hine & Zuidema, 1970; Wolf et al , 1956; Smyth et al, 1962). The oral LD50 in rats of 3523 mg/kg for mixed xylenes is derived from what is considered to be the key study (NTP, 1986) as the most recent with the lowest reported LD50 value.

Human information

No relevant information sourced

 

Acute toxicity: inhalation

Non-human information

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 recent 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.  A 4 hr rat value for mixed xylene (composition undefined) is available from a lower reliability study by Hine (1970). Other non-guideline data are available for rats and mice after 6 hr acute exposure (data from Bonnet et al, 1979).  Results for p-xylene and mixed xylene following a 4 hr (near guideline exposure) indicate a limited potential hazard.

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 as established in Directive 2000/39/EC of 8 June 2000.

 

Acute toxicity: dermal

Non-human information

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. 

Human information

No relevant information sourced

Justification for selection of acute toxicity – oral endpoint
For mixed xylenes 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 xylenes).

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 xylenes, an LC50 of 27,571 mg/m³ has been reported (Hine and Zuidema, 1970).
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.

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 xylenes (Hine and Zuidema, 1970).
Note: Although xylene isomers (including mixed xylenes) 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.

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.