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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

Endpoint:
developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP status unknown, guideline study, published in peer reviewed literature, no restrictions, fully adequate for assessment.

Data source

Referenceopen allclose all

Reference Type:
publication
Title:
Unnamed
Year:
2003
Reference Type:
publication
Title:
Benchmark Dose Technical Guidance Document
Author:
US-EPA
Year:
2010
Bibliographic source:
Available from: http://www.epa.gov/raf/publications/pdfs/benchmark_dose_guidance.pdf

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Deviations:
no
GLP compliance:
not specified
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
≥ 99.5 % pure

Test animals

Species:
rat
Strain:
Sprague-Dawley
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: IFFA CREDO Breeding Laboratories (Saint-Germain-sur-l'Arbresle, France)
- Body weight at study initiation: 180 - 200 g
- Housing: Individually in clear polycarbonate cages with stainless-steel wire lids and corn cob granules as bedding
- Diet: Food pellets (UAR Alimentation Villemoisson, France) ad libitum except during exposures
- Water: filtered tap water ad libitum except during exposures
- Acclimation period: 2 weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 21±2°C
- Humidity: 50±5%
- Photoperiod: 12 hrs dark / 12 hrs light

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure (if applicable):
whole body
Vehicle:
other: air
Details on exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 200 L glass/stainless steel inhalation chambers with dynamic and adjustable laminar air flow (6-8 m3/h), maintained at a negative pressure of ≤3 mm water.
- System of generation: The system consisted of passing an additional air-flow rate through the fritted disk of a heated bubbler containing the test chemical. Chamber concentrations were obtained by changing the temperature of the bubbler and/or the air flow rate through the fritted disk of the bubbler. The vaporized compounds were introduced into the main air-inlet pipe of the exposure chambers.
- Temperature, humidity, pressure in air chamber: 23±2°C, 50±5%

TEST ATMOSPHERE
- Brief description of analytical method used: gas chromatography with a flame ionization detector
- Samples taken from breathing zone: no data
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
The actual concentrations were determined by gas chromatography with a flame ionization detector. The column temperature was maintained at 100°C. The concentrations determined by analyses were essentially the same as the target concentrations.
Details on mating procedure:
Nulliparous females were housed overnight with adult males (one male to two or three females) from the same strain and supplier. The day that vaginal smears were found to be sperm-positive was considered day 0 of gestation (GD).
Duration of treatment / exposure:
6 hr/day
Frequency of treatment:
Daily, from day 6 through 20 of gestation.
Duration of test:
21 days
No. of animals per sex per dose:
23 - 26 mated females/group; 20 - 26 pregnant females/group
Control animals:
yes, concurrent vehicle
Details on study design:
Control animals were exposed concurrently to filtered room air in an adjacent chamber identical to those of the treatment groups.

Examinations

Maternal examinations:
CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes - recorded on GD 0, 6, 13 and 21
- Body weight changes were calculated for the following gestation intervals: 0-6, 6-13 and 13-21.
- The corrected weight gain was the body weight gain between GD 6-21 subtracted from gravid uterus weight.

FOOD CONSUMPTION: Yes - Measured for the intervals GD 6-13 and 13-21

POST-MORTEM EXAMINATIONS: Yes - Sacrifice on gestation day 21
- Organs examined: Uterus
Ovaries and uterine content:
The uterus was removed and weighed. The number of corpora lutea, implantation sites, resorptions, and dead and live foetuses were recorded. Uteri with no visible implantation sites were stained with ammonium sulphide (10%) to detect very early resorptions.
Fetal examinations:
Live foetuses were weighed, sexed, and examined for external anomalies including those of the oral cavity. Half of the live foetuses from each litter were preserved in Bouin's solution and examined for internal soft tissue changes. The other half were fixed in ethanol (70%), eviscerated, and then processed for skeletal staining with Alizarin Red S for subsequent skeletal examination.
Statistics:
Where appropriate, the data were presented as mean ± SD. One-way analysis of variance was used to analyse the number of corpora lutea, implantation sites and live foetuses, maternal food consumption and body weights and was followed by Dunnett's test where differences were found. The Kruskal-Wallis test was used to evaluate the percentages of non-live implants, resorptions, and males, and the proportions of foetuses with alterations in each litter and was followed by the Mann-Whitney test where appropriate. Pregnancy rates and percentages of litters with any malformations or with external, visceral or skeletal variations were analysed using Fisher's test. Least-squares analysis was carried out where applicable. The level of statistical significance reported was P<0.05. The litter was the unit of analysis for foetal variables.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:yes

Details on maternal toxic effects:
No test dams died. Exposure to 2000 ppm led to significant decreases in the weight of dams on GD 13 and GD 21. Maternal weight gain and food consumption were significantly reduced during the first half of exposure at 1000 ppm and for the entire exposure period at 2000 ppm. Corrected weight gain was significantly depressed at 1000 and 2000 ppm (by 32 and 82% respectively).

Effect levels (maternal animals)

Dose descriptor:
BMCL10
Remarks:
m-xylene
Effect level:
898 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:yes

Details on embryotoxic / teratogenic effects:
No adverse effects were observed on the average number of implantations and live foetuses, the incidence of non live implants and resorptions, or on the foetal sex ratio. Foetal body weights were significantly lower than control at 1000 and 2000 ppm (6 and 14-15%, respectively). Foetal variations were distributed evenly across all groups except for a slight increase in the incidence of incompletely ossified thoracic centra at 2000 ppm compared to the concurrent control.

Effect levels (fetuses)

Dose descriptor:
BMCL10
Remarks:
m-xylene
Effect level:
1 022 ppm (nominal)
Based on:
test mat.
Basis for effect level:
other: Developmental Toxicity

Fetal abnormalities

Abnormalities:
not specified

Overall developmental toxicity

Developmental effects observed:
not specified

Applicant's summary and conclusion

Conclusions:
The BMC10 for maternal toxicity was 898 ppm, and the BMC10 for foetal effects was 1022 ppm. Hence maternal toxicity (as indicated by a reduction in corrected maternal body weight gain) occured at exposures that were lower than those resulting in a biologically meaningful (>10%) reduction in foetal body weight.
Executive summary:

Inhalation exposure of m-xylene by Sprague-Dawley rats from gestation days 6-20 resulted in maternal toxicity at 1000 and 2000 ppm. Foetal toxicity at 1000 and 2000 ppm was seen, in the presence of maternal toxic effects. m-xylene was not teratogenic up to 2000 ppm.