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Toxicological information

Repeated dose toxicity: inhalation

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Administrative data

Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-guideline animal experimental study, published in peer-reviewed literature, GLP status unknown, fully adequate for assessment.

Data source

Reference
Reference Type:
publication
Title:
Unnamed
Year:
2001

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Brain morphological investigations 8 weeks following exposure. Brainstem auditory-evoked responses used to determine auditory thresholds at different frequencies. The cochlea and organ of Corti examined by light and electron microscopy, respectively.
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Analytical purity: >99%
Source: Acros, Geel, Belgium

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Iffa Credo, Domaine des Oncines, Saint-Germain-sur l’Arbresle, France
- Age at study initiation: 14 weeks
- Diet: UAR-Alimentation, Villemoisson, Epinay-sur-Orge, France; sterilized with γ-ray, ad libitum
- Water: Filtered tap water (pore size 0.3 µm) ad libitum
- Acclimation period: 6 days

ENVIRONMENTAL CONDITIONS
- Temperature: 22°C
- Humidity: 55 ± 5% %
- Photoperiod: 12 hrs dark / 12 hrs light

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
other: air
Details on inhalation exposure:
- Exposure apparatus: 200 L stainless steel inhalation chambers designed to maintain a dynamic and adjustable airflow (10-30 m3/hr), maintained at negative pressure (2-3 mm H2O)
- System of generation: An additional airflow was bubbled through xylene and the output vapour was diluted with air to the required concentration before entering the exposure chamber.
- Temperature, humidity, pressure in air chamber: no data
- Air flow rate: 10-30 m3/hr

TEST ATMOSPHERE
- Brief description of analytical method used: m-xylene concentrations in the exposure chambers were continuously monitored using a gas liquid chromatograph.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Achieved exposure concentrations were determined once during each 6 hr exposure period (sample collection on activated charcoal and analysis by gas chromatography).
Duration of treatment / exposure:
13 weeks followed by 8 week recovery period
Frequency of treatment:
6 hours/day, 5 days/week
Doses / concentrationsopen allclose all
Remarks:
Doses / Concentrations:
0, 450, 900, 1800 ppm
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
0, 1954, 3908, 7817 mg/m3
Basis:
nominal conc.
No. of animals per sex per dose:
16
Control animals:
yes, sham-exposed
Details on study design:
Study aim – evaluation of potential ototoxicity in rats of xylene isomer by electrophysiological methods. Auditory thresholds at different frequencies were determined by brainstem auditory evoked responses. A quantitative morphological study (histocochleogram) and scanning electron microscopy of the organ of Corti used to determine whether there were any microscopic alterations.

Dose selection rationale – based on preliminary range-finding studies. The highest exposure concentration was chosen to produce a reduction in body weight gain of less than 10% and no mortality after four weeks of exposure.

Examinations

Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes

NEUROPHYSICAL MEASUREMENTS: Yes
Sacrifice and pathology:
GROSS PATHOLOGY: No data

MORPHOLOGY: Yes
Statistics:
Continuous, parametric variables - Bartlett's test for homogeneity of variances (Bartlett 1937) and by analysis of variance. If the analysis of variance was significant, individual mean comparisons were made with Scheffe's multiple range test to realize comparisons between any pair of groups. Non-parametric data (audiometric thresholds) - Kruskal-Wallis test (Kruskal & Wallis 1952; Gad & Weil 1986). The probability value of P<0.05 was used as the critical level of significance.

Results and discussion

Results of examinations

Body weight and weight changes:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Details on results:
CLINICAL SIGNS AND MORTALITY: No mortality, all rats remained in good health.

BODY WEIGHT AND WEIGHT GAIN: No statistically significant differences.

NEUROPHYSICAL EXAMINATION: No effect on the latency or amplitudes of brainstem auditory evoked responses or audiometric thresholds.

MORPHOLOGICAL STUDY: There was no loss of hair cells either in the inner or outer hair cell rows of the organ of Corti.

Effect levels

open allclose all
Dose descriptor:
NOAEC
Effect level:
1 800 ppm
Sex:
male
Basis for effect level:
other: equivalent to 7817 mg/m3, no significant effects on bodyweight and bodyweight gain at highest dose tested
Dose descriptor:
NOAEC
Remarks:
ototoxicity
Effect level:
1 800 ppm
Sex:
male
Basis for effect level:
other: equivalent to 7817 mg/m3, no alteration in auditory evoked response or structure / ultrastructure of the organs of hearing at highest dose tested

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
There were no changes in brainstem auditory evoked responses or alterations in structure of the cochlea or ultrastructure of the organ of Corti in male rats 8 weeks after cessation of sub-chronic exposure to m-xylene.
Executive summary:

Male Sprague-Dawley rats were exposed to m-xylene by inhalation (0, 450, 900 and 1800ppm (equivalent to 0, 1954, 3908, 7817 mg/m3) 6 hr/day, 5 days/week for 13 weeks) and brainstem auditory-evoked responses were determined 8 weeks after treatment ended. The cochlea and organ of Corti were examined using light or electron microscopy, respectively. No functional or structural alterations were present, with an overall NOAEC of 1800 ppm for ototoxicity.