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Toxicological information

Developmental toxicity / teratogenicity

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Administrative data

developmental toxicity
Type of information:
experimental study
Adequacy of study:
key study
Study period:
25.02.1985 - 09.03.1985
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
comparable to guideline study

Data source

Referenceopen allclose all

Reference Type:
Hydroquinone: A developmental toxicity study in rats
Krasavage WJ, Blacker AM, English JC & Murphy SJ
Bibliographic source:
Fundam Appl Toxicol 18, 370 – 375
Reference Type:
study report
Report date:

Materials and methods

Test guideline
equivalent or similar to guideline
OECD Guideline 414 (Prenatal Developmental Toxicity Study)
not applicable
GLP compliance:
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Details on test material:
Physical state: white crystalline solid
Purity: > 99 %
Supplier: Eastman Kodak Co. (#356)
Batch: A13
GC analysis revealed that the batch was > 99 % pure both before and after the treatment period.

Test animals

other: COBS-CD-(SD)BR
Details on test animals or test system and environmental conditions:
Source: Charles River Labs., Inc., Lakeview
Age at study initiation: 10 - 11 w
Weight at study initiation: 215 - 216 g
Diet: ad lib
Water: ad lib
Acclimation period: 4 w

Temperature (°C): 20 - 24.4
Humidity (%): 45 - 50
Photoperiod (hrs dark / hrs light): 12 / 12

Administration / exposure

Route of administration:
oral: gavage
Details on analytical verification of doses or concentrations:
Hydroquinone was administered to the animals as a 5 % solution in distilled water, prepared daily. Test solutions prepared on the first 2 days of dosing were analyzed (GC) for HQ concentration prior to use. For the remainder of the study, only the solutions prepared on Monday, Wednesday, and Friday were analyzed. On some days of analysis, the test solutions were analyzed both prior to and after dosing and were found to be stable over this period. The mean concentrations for the test solutions of HQ used during the study were within +/- 6 % of the desired concentration.
Details on mating procedure:
The rats were mated 1:1 over a 4-day period to obtain 120 inseminated females. Copulation was confirmed by the presence of a vaginal plug, and the day a plug was found was considered day 0 of gestation. Inseminated females were assigned to the treatment and control groups on the basis of the day 0 body weight using a computer-generated randomization program.
Duration of treatment / exposure:
gestation days 6 - 15
Frequency of treatment:
once daily
Duration of test:
sacrifice on gestation day 20
Doses / concentrationsopen allclose all
Dose / conc.:
0 mg/kg bw/day
Dose / conc.:
30 mg/kg bw/day
Dose / conc.:
100 mg/kg bw/day
Dose / conc.:
300 mg/kg bw/day
No. of animals per sex per dose:
30 f
Control animals:
yes, concurrent vehicle


Maternal examinations:
Maternal body weights were recorded on gestation days 0, 6, 9, 12, 16, and 19.
Individual feed consumption was measured from days 0-6, 6-9, 9-12, 12-16, and 16-19 of gestation.
Cage-side observations for clinical signs of maternal toxicity were conducted twice each workday on non-treatment days. On treatment days, clinical observations were made prior to and after treatment and at the end of the workday.
A detailed examination, including but not limited to examination of the hair, skin, eyes, general activity, faeces, and urine, was conducted on each female on the days body weights were recorded.
On day 20 of gestation, the females were anesthetized and the abdominal and thoracic viscera were exposed. Terminal body weights were recorded and gravid uteri, with ovaries attached, were removed and weighed.
A necropsy examination of the thoracic and abdominal viscera was conducted in situ on each female. The liver and kidneys were removed, trimmed of extraneous tissue, and weighed for organ/body weight comparisons. Samples of these organs were preserved in 10 % neutral buffered formalin.
Ovaries and uterine content:
After the gravid uterus was weighed, the uterine horns were opened, and the implantation sites were counted and categorized as viable/dead foetus and late/early resorption.
The ovaries were dissected free and trimmed of extraneous tissue, and the corpora lutea of pregnancy were counted. The uteri of apparently non-pregnant females were stained with a 10 % solution of sodium sulfide and examined for the presence of micro-implantation sites.
Fetal examinations:
Viable foetuses were removed from the uterus, blotted dry on absorbent material, sexed, weighed individually, and examined for external abnormalities. Approximately one-half of the foetuses from each litter were preserved in Bouin's solution and examined for internal soft tissue changes using Wilson's free-hand razor blade technique. The other half of the foetuses were fixed in 95 % ethanol, macerated in 2 % potassium hydroxide, stained with alizarin red S, and examined for skeletal malformations and variations.
Statistical analyses compared the HQ groups with the control group using the SAS software package. Incidence data (pregnancy rate, percentage pre- and post-implantation loss, incidence of foetuses with malformation/variation, incidence of litters with foetuses with malformation/variation, etc.) were analyzed using X2 contingency tables and Fisher's exact test when X2 was significant. Continuous data (maternal body weight, feed consumption, organ weights, foetal body weights, foetuses/litter, etc.) were analyzed using a one-way analysis of variance and Duncan's multiple-range test when the F value was significant. Bartlett's test was used to test the equality of variances (p <= 0.01). Schematic analyses were performed on the litter data to determine normality of distribution, and arcsine transformations were performed to normalize the distribution prior to analysis using the ANOVA. All analyses, except Bartlett's test, were conducted at p <= 0.05 and a two-tailed risk level.
number of females inseminated, number of females pregnant (%), number of litters with resorptions (%), litters completely resorbed, corpora lutea/dam, implantations/dam, pre-implantation loss (%), viable foetuses/litter, resorption/litter, dead foetuses/litter, post-implantation loss (%), mean foetal body weight, gravide uterine weight, corrected body weight, sex ratio

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:
Maternal toxic effects:yes. Remark: 300 mg/kg: reduction in body weight gain and feed consumption

Details on maternal toxic effects:
Mean maternal body weights of the high-dose animals (300 mg/kg) were slightly lower than the control mean body weights from the 3rd day of treatment to the end of the study. These differences were due to a significantly reduced body weight gain during the first 3 days of treatment. The mean body weight gain for the high-dose dams was significantly reduced during the treatment period (gestation days 6-16). The mean corrected body weight (day 20 body weight minus the gravid uterine weight) of the 300 mg/kg group was also slightly less than the control (difference was not statistically significant).
Feed consumption for the 300 mg/kg dams was significantly reduced during the treatment period.
Body weight and feed consumption of the dams in the low and intermediate treated groups were not different from controls. The only treatment-related clinical sign was the brownish coloration of the urine noted during treatment (all treated animals).
Mean absolute and relative weights of the liver and kidneys were comparable between treated and control dams.
Histological examinations of the livers and kidneys of the high-dose and control dams revealed no treatment-related lesions, therefore tissues from the intermediate-and low-dose dams were not examined.

Effect levels (maternal animals)

Dose descriptor:
Effect level:
100 mg/kg bw/day
Based on:
test mat.
Basis for effect level:
body weight and weight gain
food consumption and compound intake

Results (fetuses)

Fetal body weight changes:
effects observed, treatment-related
External malformations:
no effects observed
Skeletal malformations:
no effects observed
Visceral malformations:
no effects observed
Details on embryotoxic / teratogenic effects:
Embryotoxic / teratogenic effects:no effects

Effect levels (fetuses)

Dose descriptor:
Effect level:
100 mg/kg bw/day
Based on:
test mat.
Basis for effect level:
fetal/pup body weight changes

Overall developmental toxicity

Developmental effects observed:

Any other information on results incl. tables

Observations at Caesarean Section:

No significant changes in reproductive indices. A lower mean foetal body weight seen at the 300 mg/kg dose level was associated with the slightly reduced body weights seen for the dams at this dose level.

Foetal observations:

The anatomic changes were classified as malformations or aberrations (variations, retardations, and deviations). External, internal soft tissue and skeletal examinations of the foetuses revealed no subtance related malformations. Major malformations (considered to have occurred spontaneously) included micrognathia and incomplete closure of the palatine bone in one control foetus, a diaphragmatic hernia in one foetus from a 300 mg/kg litter, and a mal-positioned right subclavian artery in one foetus from a 30 mg/kg litter. The numbers of foetuses with fewer than four ossification sites in the sternum (considered as malformation) were 3, 1, 2, and 3, respectively, for the 0, 30, 100 and 300 mg/kg groups. External variations consisted of small hematomas on single foetuses in the control and 30/100 mg/kg groups and on three foetuses from the 300 mg/kg group.

Internal soft tissue aberrations included dilated renal pelves (due to shortened renal papillae), hydronephrosis (absent renal papillae), and hydroureter. Although these changes were seen more frequently in the treated groups vs. controls, the incidences were not dose related. When analyzed individually and as total soft tissue alterations, the incidence of foetuses with an alteration and the percentage of litters with at least one foetus with an alteration were not statistically different from controls.

Skeletal variations included partial ossification or non-ossification of some intra-membranous bones of the skull and the hyoid bone and variations in vertebral development, such as partial ossification or non-ossification of the first and second thoracic centra, bilobed or split thoracic centra (particularly the 10th, 11th, and 12th), and partially ossified 3rd and 4th sacral arches, which were seen in many of the foetuses from all dose levels including controls. A few foetuses had rib variations. The total number of foetuses with a vertebral variation was statistically significantly greater in the 300 mg/kg group compared with controls, but analyses of individual skeletal variations, including individual vertebral variations, and statistical analysis of total number of foetuses with a skeletal alteration indicated no significant effects on skeletal development in the treated groups compared with controls.

Applicant's summary and conclusion

This study gave no indication for a potential developmental or reproductive hazard of hydroquinone.
Executive summary:

In this study comparable to OECD Guideline 414, pregnant COBS-CD-BR rats were dosed with 0, 30, 100 or 300 mg/kg bw by gavage on days 6 – 15 of gestation. Maternal effects included a slight but significant reduction in body weight gain and feed consumption at 300 mg/kg bw. Reproductive indices (i.e. pregnancy rate, numbers of corpora lutea, implantation sites, viable foetuses, and early and late resorptions, foetal sex ratio, pre- and post-implantation losses, and gravid uterine weights) were not affected by treatment. A slightly reduced mean foetal body weight at 300 mg/kg bw was associated with a slightly reduced body weight gain for the dams at this dose level. Gross external, internal soft tissue, and skeletal examinations of the foetuses revealed no treatment telated malformations. The incidences of gross external variations (small hematomas) and internal soft tissue variations (dilated renal pelvis, hydronephrosis, and hydroureter) in treated litters were not statistically different from the control incidences. Skeletal variations (delayed ossification of membranous skull bones, hyoid bone, thoracic centra 1-3, sacral arches 3 and 4, and bilobed thoracic centra 9-13) occurred with similar frequency in controls and treated groups. The incidences of total skeletal variations were not statistically different between the control and the treated groups.

The NOEL for both maternal and developmental toxicity was 100 mg/kg bw (NOAEL of 300 mg/kg bw).