Triisodecyl benzene-1,2,4-tricarboxylate

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

No other studies available.

Link to relevant study records

Reference

Endpoint:

toxicity to reproduction

Remarks:

other: screening

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP compliant study conducted according to internationally recognised test methods. Some (minor) details on test method / results not available

Qualifier:

according to guideline

Guideline:

OECD Guideline 421 (Reproduction / Developmental Toxicity Screening Test)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Crj:CD:SD

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Japan
- Age at study initiation: (P) x 10 wks;
- Weight at study initiation: (P) Males: 373-435 g; Females: 217257 g
- Fasting period before study: No
- Housing: wire mesh cages, in pairs for mating
- Use of restrainers for preventing ingestion (if dermal): Not applicable
- Diet (e.g. ad libitum): yes, pelleted diet, CRF-1. Oriental Yeast Co. Ltd.
- Water (e.g. ad libitum): yes, tap water via automatic watering system
- Acclimation period: 14d for males; 10d for females

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23+/- 3
- Humidity (%): 55+/-10
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12:12

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Prepared weekly by dissolving required weight of TOTM in corn oil and stored in airtight containers in the dark until use.


VEHICLE
- Justification for use and choice of vehicle (if other than water): TOTM is poorly soluble in water
- Concentration in vehicle: As required to achieve nominal dose
- Amount of vehicle (if gavage): 5ml/kg
- Lot/batch no. (if required): No batch number reported but supplied by Katayama Chemical

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: up to 14 d (until sperm detected in vagina).
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy
- After successful mating each pregnant female was caged (how): singly
- Any other deviations from standard protocol: None reported

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

No data

Duration of treatment / exposure:

Males: from 14 days before pairing for 46d;
Females: from 14d before pairing to d3 of lactation

Frequency of treatment:

Daily during treatment periods see above

Remarks:

Doses / Concentrations:
0 (control) 100 300 1000 mg/kg/day
Basis:
nominal conc.

No. of animals per sex per dose:

12 males & 12 females

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: based on results of 14d preliminary study. Effects on body weight in animals given 1000 mg/kg/day
- Rationale for animal assignment (if not random): Random, stratified body weight

Positive control:

No

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily, parents & foetuses

DETAILED CLINICAL OBSERVATIONS: No data
- Time schedule:

BODY WEIGHT: Yes
- Time schedule for examinations: Males: Predose, 2, 5, 7, 10 & 14d & weekly thereafter until sacrifice; females: Predose, 2, 5, 7, 10 & 14d. Gestation period: 0, 1, 3, 5, 7, 10, 17 & 20d. Lactation period: 0,1 & 4d.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes - at same intervals as body weight except lactation period and day of sacrifice for males and 0d of gestation & lactation for females.

WATER CONSUMPTION AND COMPOUND INTAKE (if drinking water study): No data
- Time schedule for examinations:

Oestrous cyclicity (parental animals):

Examined pre-dose and during dosing period

Sperm parameters (parental animals):

Parameters examined in 5 P males/group : yes
[testis weight, epididymis weight, sperm count in testes, sperm count in epididymides, enumeration of cauda epididymal sperm reserve, sperm morphology

Litter observations:

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring:
number and sex of pups, stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain, physical or behavioural abnormalities, :

GROSS EXAMINATION OF DEAD PUPS:
yes, for external and internal abnormalities; possible cause of death was/was not determined for pups born or found dead

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals 1d after mating
- Maternal animals: All surviving animals d4 of lactation; if did not mate 1d after mating period ended
GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations of all organs & including the cervical, thoracic, and abdominal viscera. Pups: all organs

HISTOPATHOLOGY / ORGAN WEIGHTS
The following tissues were prepared for microscopic examination and weighed, respectively. : organ weights: males Testis & epididymis; females ovary;
microscopic examination: Testis & epididymis, sertoli cell count, spermatocytes, round & elongated spermatids in seminiferous tubules of 5 animals /group (Stage 1-VI, VII-Viii, IX-XI, XII-XIV of spermatoan formative cycle).
Females: Ovary

Postmortem examinations (offspring):

SACRIFICE
- The F1 offspring were sacrificed at 4 days of age.
- These animals were subjected to postmortem examinations (macroscopic and/or microscopic examination). Pups: found dead & abnormalities

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.

Statistics:

Chi squared test for 1 grade positive data and Fisher's test for other. Bartlett's /Kruskal Wallis' test for 2 or more positive grade data. Dunnett's test or Mann-Whitney U test for assessment.

Reproductive indices:

Copulation Index: No. of pairs with successful copulation/no. of pairs mated X 100
Fertility Index: No of pregnant females/no. of pairs with successful copulation X 100
Implantation index: No. of implantation sites/no. of corporea lutea X 100
Delivery index: No. of pups born/no. of implantation sites X 100
Gestation index: No. of females with live pups delivered/no. of pregnant females X 100
Nursing index: No. of females nursing live pups/no. of females with normal delivery X 100

Offspring viability indices:

Live birth index: No. of live pups at birth/no. of pups at birth X 100
Viability index: No. of live pups on d4/no.of live pups at birth

Clinical signs:

no effects observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

See below for males

Other effects:

not examined

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

effects observed, treatment-related

Description (incidence and severity):

See below for males

Reproductive performance:

no effects observed

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS): No effects

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS): No effects

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS): See histopathology (below)

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS): No effects

ORGAN WEIGHTS (PARENTAL ANIMALS): No effects

GROSS PATHOLOGY (PARENTAL ANIMALS): No effects

HISTOPATHOLOGY (PARENTAL ANIMALS): Slightly reduced numbers of spermatocytes & spermatids in 2/12 & 11/12 animals given 300 & 1000 mg/kg/day TOTM respectively and a moderate decrease in 1/12 animals given 1000 mg/kg/day TOTM. In addition the number of cells/number of spermatids in seminiferous tubules was reduced in males given 300 mg/kg/day TOTM in stages I-VI. In males given 1000 mg/kg/day in stage I-IV numbers of spermatocytes &spermatids were reduced. In stages VII-XIV spermatocyte & spermatid numbers continued to be low & the sertolicell ratio was also reduced.

Dose descriptor:

NOEL

Effect level:

100 mg/kg bw/day

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Histopathology; sperm characterization, numbers & ratio of sertoli cells in males given 1000 mg/kg/day TOTM & reduced numbers of spermatids in animals given 300 mg/kg/day.

Dose descriptor:

NOEL

Effect level:

1 000 mg/kg bw/day

Based on:

test mat.

Sex:

female

Basis for effect level:

other: see 'Remark'

Dose descriptor:

NOEL

Effect level:

1 000 mg/kg bw/day

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Absence of effects on pup weight; sex ratio; survival index; viability index following treatment of parents with TOTM at dosages of 100, 300 or 1000 mg/kg/day.

Remarks on result:

other: Generation: pups (migrated information)

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

slightly low bodyweights & body weight gain in pups in 300 mg/day/kg group.

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings:

no effects observed

Description (incidence and severity):

Pups found dead or with abnormalities only

VIABILITY (OFFSPRING): No effects

CLINICAL SIGNS (OFFSPRING): No effects

BODY WEIGHT (OFFSPRING):Body weight & body weight gain in pups from the 300 mg/kg/day group were slightly low. However as the body weight & body weight gain in the 100 & 1000 mg/kg/day groups were unaffected this was not considered to be a definite effect of treatment.

GROSS PATHOLOGY (OFFSPRING): No effects

HISTOPATHOLOGY (OFFSPRING): No effects

Reproductive effects observed:

not specified

See attached document (MITI Repro sreen.pdf)

Conclusions:

Repeat dose toxicity: Histopathological examination revealed reduced spermatocytes & spermatids in the testes of males given TOTM at doses of 300 or 1000 mg/kg/day. Treatment with TOTM had no effect on the appearance, condition or behaviour, body weight, food consumption, necropsy findings, weights of the testes, epididymis or ovaries, or histopathology of the ovaries. The NOELs are considered to be 100 & 1000 mg/kg/day for males & females respectively.
Reproductive & developmental toxicity: With the exception of the effects in male described above treatment with TOTM at dosages of 100, 300 or 1000 mg/kg/day had no effect on reproductive ability, organ weight or histopathology of the ovary, delivery or maternal behaviour of the dams. The NOELs are considered to be 100 & 1000 mg/kg/day for males & females respectively.

Pup post natal development: No effects of treatment with TOTM at dosages of 100, 300 or 1000 mg/kg/day were detected on viability, general appearance, body weights or autopsy findings. The NOEL is considered to be 1000 mg/kg/day for males & female offspring.

Executive summary:

In an OECD screening study of reproductive toxicity histopathological examination revealed reduced spermatocytes & spermatids in the testes of males given the substance at doses of 300 or 1000 mg/kg/day. Treatment had no effect on the appearance, condition or behaviour, body weight, food consumption, necropsy findings, weights of the testes, epididymis or ovaries, or histopathology of the ovaries. The NOELs for systemic toxicity are considered to be 100 & 1000 mg/kg/day for males & females respectively.

With the exception of the effects in males, treatment at dosages of 100, 300 or 1000 mg/kg/day had no effect on reproductive ability, organ weight or histopathology of the ovary, delivery or maternal behaviour of the dams. The NOEL for reproductive / developmental toxicity is considered to be 1000 mg/kg/day for offspring.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

500 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

GLP compliant study conducted according to internationally recognised test methods. Some (minor) details on test method / results not available therefore categorised as Klimisch 2.

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

In a repeated dose toxicity study combined with a screening study of reproductive/developmental toxicity on read-across substance, 1,2,4 -benzenetricarboxylic acid, trioctyl ester, no significant effect on reproductive ability, organ weight or histopathology of the ovary, delivery or maternal behaviour was apparent. The NOEL for reproductive / developmental toxicity was considered to be 500 mg/kg/day for both parents and offspring, the highest dose examined.

An OECD screening study of reproductive toxicity conducted with read-across substance, tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, revealed no functional changes in fertility or reproductive performance although histopathological examination revealed reduced spermatocytes & spermatids in the testes of males given the substance at doses of 300 or 1000 mg/kg/day. The NOELs for systemic toxicity were considered to be 100 & 1000 mg/kg/day for males & females respectively. The NOEL for reproductive / developmental toxicity is considered to be 1000 mg/kg/day for offspring. However, in a 90 day repeated dose study conducted with an identical highest dose (1000 mg/kg/day), which had a duration approximately double that of the screening study, a detailed evaluation of the testes was performed in high dose animals and controls and no treatment-related effects were observed (see IUCLID Chapter 7.5.1).

A two-generation reproductive toxicity study is required in accordance with Section 8.7.3 of Column 1, Annex IX. It is proposed to waive the need to conduct this study based on the results of a repeated dose toxicity study combined with a screening study of reproductive/developmental toxicity on read-across substance, 1,2,4 -benzenetricarboxylic acid, trioctyl ester, which showed no significant effect on reproductive ability, organ weight or histopathology of the ovary, delivery or maternal behaviour. The NOEL for reproductive / developmental toxicity was considered to be 500 mg/kg/day for both parents and offspring, the highest dose examined. In addition, in a 90 day repeated dose study with read-across substance, tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, a detailed examination of the testes was performed in high dose animals and no effects were observed.

Short description of key information:
In a repeated dose toxicity study combined with a screening study of reproductive/developmental toxicity on a different read-across substance, 1,2,4 -benzenetricarboxylic acid, trioctyl ester, no significant effect on reproductive ability, organ weight or histopathology of the ovary, delivery or maternal behaviour was apparent. The NOEL for reproductive / developmental toxicity was considered to be 500 mg/kg/day for both parents and offspring, the highest dose examined.

Justification for selection of Effect on fertility via oral route:
It is considered that this study provides the most reliable results. Testicular effects seen in the supporting study were not observed in the 90 day repeated dose toxicity study.

Justification for selection of Effect on fertility via inhalation route:
The oral route is considered the most appropriate route of exposure.

Justification for selection of Effect on fertility via dermal route:
The oral route is considered the most appropriate route of exposure.

Effects on developmental toxicity

Description of key information

In a developmental toxicity study with read-across substance, tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, the NOEL for maternal toxicity was 1050 mg/kg/day, the NOEL for pre-natal developmental toxicity: 1050 mg/kg/day and the for NOEL post-natal evaluation of offspring was 500 mg/kg/day.

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2000-2001

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP compliant study conducted according to internationally recognised test methods

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Details on test animals or test system and environmental conditions:

No details available

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: No details available

Analytical verification of doses or concentrations:

not specified

Details on mating procedure:

No details available

Duration of treatment / exposure:

Gestation days 6-19 (prenatal development)
Gestation day 6 - post-partum day 20 (post-natal development)

Frequency of treatment:

Daily, except day of parturition for animals allowed to litter

Remarks:

Doses / Concentrations:
0, 100, 500, 1050 mg/kg
Basis:
nominal conc.

No. of animals per sex per dose:

35 females/group - 20 for pre-natal development; 15 for post-natal development

Control animals:

yes, concurrent vehicle

Details on study design:

No details available

Maternal examinations:

CAGE SIDE OBSERVATIONS: No data

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: No data

POST-MORTEM EXAMINATIONS: No data

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: No data

Fetal examinations:

- External examinations: Yes
- Soft tissue examinations: Yes
- Skeletal examinations: Yes
- Head examinations: No data

Statistics:

ANOVA followed by William’s test, or Kruskal-WaIlis/Hollander & Wolfe followed by Shirley’s test, Steel’s test, Cochran-Armitage, Fisher’s exact test.

Indices:

No data

Historical control data:

No data

Details on maternal toxic effects:

Maternal toxic effects:no effects

Details on maternal toxic effects:
No significant effects on bodyweight or gravid uterus weight at any dose level, either during gestation or lactation. No inter-group differences regarding the number of implantations, post-implantation loss, gestation length and index, or (live) litter size.

Dose descriptor:

NOAEL

Effect level:

1 050 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

Dose descriptor:

NOAEL

Effect level:

1 050 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Dose descriptor:

NOAEL

Effect level:

500 mg/kg bw/day

Based on:

test mat.

Basis for effect level:

other: other:

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
No significant differences in foetal body weights. No significant variations or malformations observed in gross external appearance, viscera, skeletal system, or anogenital distance of pups.

Abnormalities:

not specified

Developmental effects observed:

not specified

Post-natal development examinations did not reveal any significant differences relative to controls for survival of offspring, sex ratio, bodyweight or bodyweight gain, auditory startle and pupil closure responses, age at vaginal opening or preputial separation.

At necropsy, there were no effects attributable to treatment in either females (6 weeks of age) or males (15 weeks of age). Assessment included morphology of the male and female reproductive tract organs, weight of the male reproductive organs or microscopic pathology of the testis.

 

There was a slight but statistically significant (P<0.05) increase in the number of male animals with retained areolar regions on evaluation at post-natal Day 13 at 1050 mg/kg/day. Affected animals had only one or two more sites than those in the control group. The areolae present at post-natal Day 13 were no longer present on re-examination on post-natal Day 18. In the absence of any other supporting data, this finding was regarded as being of questionable toxicological significance.

There was a higher incidence of displaced testes in foetuses from the group treated at 1050 mg/kg/day when compared with controls. However, the incidence was within the range of recent historical control data of the test facility for this endpoint. No displaced testes were noted in any of the foetuses undergoing less rigorous examination prior to preparation for skeletal examination. There was no difference in the incidence of non-scrotal testes between males of treatment and control groups at 15 weeks of age.

The incidence of renal cavitation was higher controls in foetuses that were macroscopically assessed prior to skeletal examination. Again, this finding was within the range of recent historical control values, and was not found during examination of foetuses by the more rigorous serial sectioning technique.

The incidence of effects in the testes and kidneys appear to be related to the low incidence of these findings in the concurrent control group compared to the range of historical control values. The observed incidences of these findings in treated groups were within the range of historical controls from recent studies at the test facility and they were not supported by complimentary observations made in foetuses or offspring. They were therefore considered not to be related to treatment.

 

Conclusions:

A developmental toxicity study in the rat, extended to permit an assessment of post-natal development, found no treatment-related effects indicative of maternal toxicity. No effects on offspring body weights or litter viability were observed. No developmental (teratogenic) effects were observed and there were no effects upon sexual maturation or development of the reproductive tract in male or female offspring that were attributed to treatment.

NOEL maternal toxicity: 1050 mg/kg/day
NOEL pre-natal developmental toxicity: 1050 mg/kg/day
NOEL post-natal evaluation of offspring: 500 mg/kg/day; LOAEL: 1050 mg/kg/day

Executive summary:

A developmental toxicity study in the rat, extended to permit an assessment of post-natal development, found no treatment-related effects indicative of maternal toxicity. No effects on offspring body weights or litter viability were observed. No developmental (teratogenic) effects were observed and there were no effects upon sexual maturation or development of the reproductive tract in male or female offspring that were attributed to treatment.

NOEL maternal toxicity: 1050 mg/kg/day

NOEL pre-natal developmental toxicity: 1050 mg/kg/day

NOEL post-natal evaluation of offspring: 500 mg/kg/day; LOAEL: 1050 mg/kg/day

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

500 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

GLP compliant study conducted according to internationally recognised test methods therefore categorised as Klimisch 1.

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

A developmental toxicity study in the rat with read-across substance, tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, extended to permit an assessment of post-natal development, found no treatment-related effects indicative of maternal toxicity. No effects on offspring body weights or litter viability were observed. No developmental (teratogenic) effects were observed and there were no effects upon sexual maturation or development of the reproductive tract in male or female offspring that were attributed to treatment.

NOEL maternal toxicity: 1050 mg/kg/day

NOEL pre-natal developmental toxicity: 1050 mg/kg/day

NOEL post-natal evaluation of offspring: 500 mg/kg/day; LOAEL: 1050 mg/kg/day (slight increase in retained areolar region in males treated at 1050 mg/kg/day post-natal Day 13, no longer present post-natal day 18 and slightly higher increase in displaced testes compared to controls although the observed incidence was within the range of historical control data).

Justification for selection of Effect on developmental toxicity: via oral route:
Only 1 study available.

Justification for selection of Effect on developmental toxicity: via inhalation route:
The oral route is considered the most appropriate route of exposure.

Justification for selection of Effect on developmental toxicity: via dermal route:
The oral route is considered the most appropriate route of exposure.

Justification for classification or non-classification

In a repeated dose toxicity study combined with a screening study of reproductive/developmental toxicity on read-across substance, 1,2,4 -benzenetricarboxylic acid, trioctyl ester, no significant effect on reproductive ability, organ weight or histopathology of the ovary, delivery or maternal behaviour was apparent. The NOEL for reproductive / developmental toxicity was considered to be 500 mg/kg/day for both parents and offspring, the highest dose examined.

An OECD screening study of reproductive toxicity conducted with read-across substance, tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, revealed no functional changes in fertility or reproductive performance although histopathological examination revealed reduced spermatocytes & spermatids in the testes of males given the substance at doses of 300 or 1000 mg/kg/day. The NOELs for systemic toxicity were considered to be 100 & 1000 mg/kg/day for males & females respectively. The NOEL for reproductive / developmental toxicity is considered to be 1000 mg/kg/day for offspring. However, in a 90 day repeated dose study conducted with an identical highest dose (1000 mg/kg/day), which had a duration approximately double that of the screening study, a detailed evaluation of the testes was performed in high dose animals and controls and no treatment-related effects were observed (see Section 5.6.1).

A pre- and post-natal developmental toxicity study with read-across substance, tris(2-ethylhexyl) benzene-1,2,4-tricarboxylate, revealed no effects on developmental toxicity at a dose level of 500 mg/kg/day. At the higher dose level of 1050 mg/kg/day a slight increase in retained areolar region was observed in males on post-natal Day 13 which was no longer present post-natal day 18. A slightly higher increase in displaced testes compared to controls was also seen although the observed incidence was within the range of historical control data.

In accordance with Regulation (EC) No. 1272/2008, effects such as small changes in semen parameters or in the incidence of spontaneous defects in the foetus, small changes in the proportions of common foetal variants such as are observed in skeletal examinations, or in foetal weights, or small differences in postnatal developmental assessments are considered to be of low or minimal toxicological significance insufficient to warrant classification.