2,4-dimethyl-6-(1-methyl-pentadecyl)phenol

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

21 Oct 2013 - 06 May 2014

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: guideline compliant GLP-study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2014

Report date:

2014

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Test guideline 3

Qualifier:

according to guideline

Guideline:

EU Method B.31 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes (incl. QA statement)

Remarks:

BASF SE, Experimental Toxicology and Ecology, 67056 Ludwigshafen, Germany

Test material

Test material information

Constituent 1

Reference substance name:

2,4-dimethyl-6-(1-methyl-pentadecyl)phenol

EC Number:

411-220-5

EC Name:

2,4-dimethyl-6-(1-methyl-pentadecyl)phenol

Cas Number:

134701-20-5

Molecular formula:

C24 H42 O

IUPAC Name:

2-(hexadecan-2-yl)-4,6-dimethylphenol

Details on test material:

- Name of test material (as cited in study report): 2,4-dimethyl-6-(1-methyl-pentadecyl)phenol
- Physical state: Liquid/ yellowish
- Analytical purity: 94 area-% (corrected for water content) (see Report, Project No.: 13L00070)
- Storage condition of test material: Room temperature / under light exclusion

Test animals

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Research Models and Services, Germany GmbH
- Age at study initiation: 10-12 weeks
- Weight at study initiation: 143.0 – 190.1 g.
- Housing: individually in Makrolon type M III cages
- Diet: ad libitum ground Kliba maintenance diet mouse/rat “GLP”, meal, supplied by Provimi Kliba SA, Kaiseraugst, Switzerland.
- Water: potable tap water in water bottles ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 30-70
- Air changes (per hr): 15
- Photoperiod (hrs dark / hrs light): 12/12

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
The test substance was heated up to 40 degrees Celsius. Thereafter, the specific amount of test substance was weighed, topped up with corn oil in a graduated flask and intensely mixed by shaking until it is dissolved.

VEHICLE
- Concentration in vehicle: 0, 1250, 5000 and 25000 mg/100ml
- Amount of vehicle (if gavage): 4 ml/kg

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The analyses of the test substance preparations were carried out at the Analytical Chemistry Laboratory of Experimental Toxicology and Ecology of BASF SE, Ludwigshafen, Germany. Analytical verifications of the stability of the test substance in corn oil at room temperature under light exclusion over a period of 7 days had been verified prior to the start of the study (Project No.: 01Y0033/13Y008). Samples of the test substance preparations were sent to the analytical laboratory at the beginning of administration for verification of the concentrations. The results of the analysis of the oily test substance preparations confirmed the correctness of the prepared concentrations. The analytical values of the samples corresponded to the expected values within the limits of the analytical method, i.e. were always above 90% and below 110% of the nominal concentrations. Given that the test substance was completely miscible with corn oil, solutions were considered to be homogenous without further analysis.

Details on mating procedure:

- Impregnation procedure: purchased timed pregnant
The animals were paired by the breeder (“time-mated”); the day of evidence of mating (= detection of vaginal plug/sperm) was referred to as GD 0. The animals arrived on the same day (GD 0) at the experimental laboratory.

Duration of treatment / exposure:

The test substance preparations were administered to the animals once a day orally by gavage, from implantation to one day prior to the expected day of parturition (GD 6 to GD 19), always at approximately the same time in the morning.

Frequency of treatment:

daily

Duration of test:

On GD 20, the females were sacrificed in a randomized order.

Doses / concentrations

Remarks:

Doses / Concentrations:
50, 200, 1000 mg/kg
Basis:
nominal conc.

No. of animals per sex per dose:

25

Control animals:

yes, concurrent vehicle

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: A cage-side examination was conducted at least once daily for any signs of morbidity, pertinent behavioral changes and signs of overt toxicity. If such signs occurred, the animals were examined several times daily (GD 0-20).

BODY WEIGHT: Yes
- Time schedule for examinations: All animals were weighed on GD 0, 1, 3, 6, 8, 10, 13, 15, 17, 19 and 20. The body weight change of the animals was calculated based on the obtained results. Furthermore, the corrected body weight gain was calculated after terminal sacrifice (terminal body weight on GD 20 minus weight of the unopened uterus minus body weight on GD 6).

FOOD CONSUMPTION: Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
The consumption of food was recorded for the intervals GD 0-1, 1-3, 3-6, 6-8, 8-10, 10-13, 13-15, 15-17, 17-19 and 19-20.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day #20
After the dams had been sacrificed, they were necropsied and assessed for gross pathology, in randomized order.

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
- Other: Dead fetuses

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes: half per litter

Statistics:

- Food consumption, body weight, body weight change, corrected body weight gain (net maternal body weight change), carcass weight, weight of unopened uterus, number of corpora lutea, number of implantations, number of resorptions, number of live fetuses, proportions of preimplantation loss, proportions of postimplantation loss, proportions of resorptions, proportion of live fetuses in each litter, litter mean fetal body weight, litter mean placental weight were assessed by the Dunnett-test (two-sided)
- Female mortality, females pregnant at terminal sacrifice, number of litters with fetal findings were assessed using the Fisher's Exact test (one-sided)
- Proportions of fetuses with malformations, variations and/or unclassified observations in each litter were assessed using the Wilcoxon-test (one-sided)

Indices:

conception rate
preimplantation loss
postimplantation loss

Historical control data:

included in the report

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Details on maternal toxic effects:
- There were no test substance-related or spontaneous mortalities in any females of all test groups (0, 50, 200 or 1000 mg/kg bw/d).
- Some females (9 out of 25) of the high-dose group (1000 mg/kg bw/d) showed transient salivation during the treatment period. Salivation persisted in the respective animals only for some minutes after daily gavage dosing (i.e. up to 10 minutes) and was initially observed on GD 14. No further clinical signs or changes of general behavior, which may be attributed to the test substance, were detected in any female.
- The mean food consumption of the dams in test groups 1-3 (50, 200 and 1000 mg/kg bw/d) was generally comparable to the concurrent control throughout the entire study period.
- The mean body weights and the average body weight gains of the low-, mid- and high-dose rats (50, 200 and 1000 mg/kg bw/d) were in general comparable to the controls throughout the entire study period. The corrected body weight gain of test groups 1-3 (50, 200 and 1000 mg/kg bw/d) revealed
no difference of any biological relevance to the corresponding control group.
- The mean gravid uterus weights of the animals of test group 1-3 (50, 200 and 1000 mg/kg bw/d) were not influenced by the test substance.
- In six (out of 25) high-dose dams (1000 mg/kg bw/d) an enlarged liver was recorded during gross necropsy. This is likely to be a treatment-related finding which is however considered as adaptive rather than adverse. No necropsy findings which could be attributed to the test substance were seen in any dam of the test groups 1 and 2 (50 and 200 mg/kg bw/d).
- The conception rate was 100% in all test groups (0, 50, 200 and 1000 mg/kg bw/d). There were no test substance-related and/or biologically relevant differences between the test groups 0, 1, 2 and 3 (0, 50, 200 and 1000 mg/kg bw/d) in conception rate, in the mean number of corpora lutea and implantation sites or in the value calculated for the postimplantation loss, the number of resorptions and viable fetuses. All observed differences are considered to reflect the normal range of fluctuations for animals of this strain and age.

Effect levels (maternal animals)

1

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Details on embryotoxic / teratogenic effects:
- The sex distribution of the fetuses in test groups 1-3 (50, 200 and 1000 mg/kg bw/d) was comparable to the control fetuses.
- The mean placental weights of the low-, mid- and high-dose groups (50, 200 and 1000 mg/kg bw/d) were comparable to the corresponding control group. The statistically significantly increased placental weight of all viable fetuses in the low-dose group is considered as incidental.
- The mean fetal weights of test groups 1, 2 and 3 (50, 200 and 1000 mg/kg bw/d) were not influenced by the test substance and did not show any biologically relevant differences in comparison to the control group. However, the mean fetal weight of male fetuses was slightly, but statistically significantly decreased in test group 3 (3.5g). As this marginally changed value lay well within the historical control range (mean 3.6 [2.6-5.3]), it is considered to reflect the normal range of fluctuations for animals of this strain and age.
- External malformations were recorded for one fetus of the control and the high-dose group (1000 mg/kg bw/d), each. Male control fetus No. 18-06 had more than one malformation affecting the fetal body, i.e. short trunk, threat-like tail and pointed lower jaw. The total incidence of external malformations in treated animals did not differ significantly from the control group and was comparable to the historical control data.
- No external variations were recorded.
- One unclassified external observation, i.e. blood coagulum around placenta, was recorded in one fetus each of the mid- and high-dose group (500 and 1000 mg/kg bw/d). This finding is not considered biologically relevant.
- Soft tissue malformations were recorded for one control fetus. Male fetus No. 22-04 had more than one malformation affecting the large blood vessels, i.e. high aortic arch, absent subclavian (right side), dilated aorta and transposition of great vessels. There were no soft tissue malformations in any of the treated groups.
- Some soft tissue variations were detected in all test groups (0, 50, 200 or 1000 mg/kg bw/d), i.e. dilated renal pelvis and dilated ureter. These variations were neither statistically significantly different from control nor dose-dependent and therefore, not considered biologically relevant.
- One unclassified soft tissue observation, i.e. discolored adrenal(s), was recorded in one control fetus. This finding is not considered biologically relevant.
- One male control fetus (No. 18-06) was multiple malformed: only skull, cervical vertebrae, pelvic girdle, fore- and hindlimbs and sternum were present, most of these bones and cartilaginous parts were deformed, thus a specification of each and every detail was impractical. Furthermore, some skeletal malformations were detected in all test groups (0, 50, 200 and 1000 mg/kg bw/d) affecting the vertebrae, sternum and forelimbs. The incidences of these malformations were neither statistically significantly different from control nor dose-dependent and therefore, not considered biologically relevant.
- For all test groups, skeletal variations of different bone structures were observed, with or without effects on corresponding cartilages. The observed skeletal variations were related to several parts of fetal skeleton and were neither statistically significantly different from control nor dose-dependent and therefore, not considered biologically relevant.
- Additionally, some isolated cartilage findings without impact on the respective bony structures, which were designated as unclassified cartilage observations, occurred in all test groups. The observed unclassified cartilage findings were related to the skull, the vertebral column, the sternum and ribs and did not show any relation to dosing.

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

Under the conditions of this prenatal developmental toxicity study, the oral administration of test material to pregnant Wistar rats from implantation to one day prior to the expected day of parturition (GD 6-19) at a dose of 1000 mg/kg bw/d caused no evidence of maternal toxicity. In conclusion, the no observed adverse effect level (NOAEL) for maternal toxicity is 1000 mg/kg bw/d, the highest dose tested. The no observed adverse effect level (NOAEL) for prenatal developmental toxicity is also 1000 mg/kg bw/d. There were no toxicologically relevant adverse fetal findings evident.

Executive summary:

In a GLP-compliant study following OECD guideline 414, the test article was tested for its prenatal developmental toxicity in Wistar rats. The test substance was administered as an oily solution to groups of 25 time-mated female Wistar rats by gavage at doses of 50, 200, and 1000 mg/kg body weight/day (mg/kg bw/d) on gestation days (GD) 6 through 19. The control group, consisting of 25 females, was dosed with the vehicle (corn oil) in parallel. A standard dose volume of 4 mL/kg body weight was used for each test group. At terminal sacrifice on GD 20, 25 females per group had implantation sites. Food consumption and body weights of the animals were recorded regularly throughout the study period. The state of health of the animals was checked each day. On GD 20, all females were sacrificed by cervical dislocation (under isoflurane anesthesia) and assessed by gross pathology (including weight determinations of the unopened uterus and the placentae). For each dam, corpora lutea were counted and number and distribution of implantation sites (differentiated between resorptions, live and dead fetuses) were determined. The fetuses were removed from the uterus, sexed, weighed and further investigated for external findings. Thereafter, one half of the fetuses of each litter were examined for soft tissue findings and the remaining fetuses for skeletal (inclusive cartilage) findings.

No toxicologically relevant signs of maternal toxicity were observed in any of the control and test groups. Neither clinical observations nor determination of food consumption, body weights revealed difference between the animals receiving 50, 200 or 1000 mg/kg bw/d and controls. Enlarged livers in 6 out of 25 animals were regarded as treatment-related and adaptive findings which are indicative of the metabolic burden of the liver caused by the test substance. Some females (9 out 25) receiving the highest dose of 1000 mg/kg bw/d showed transient salivation after treatment. This salivation persisted in the respective females for a few minutes immediately after each administration. It is considered to be treatment-related, likely as a result of the bad taste of the test substance/vehicle preparation or due to local irritation of the upper digestive tract. It is not considered to be a sign of systemic toxicity.

No differences of toxicological relevance between the control and the treated groups (50, 200 or 1000 mg/kg bw/d) were determined for any reproductive parameters, such as conception rate, mean number of corpora lutea, mean number of implantations, as well as pre- and postimplantation loss. Similarly, no influence of the test compound on fetal weight and sex distribution of the fetuses was noted at any dose. Overall, there was no evidence for toxicologically relevant adverse effects of the test substance on fetal morphology at any dose.