2,4,6-tri-tert-butylphenol

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

30 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The study was conducted in accordance with a standardised guideline under GLP conditions. It was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997). The quality of the database is therefore considered to be high.

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

The reproductive toxicity of the test material was investigated in a combined repeated dose toxicity study with the reproduction / developmental toxicity screening test conducted in accordance with the standardised guidelines OECD 422 and US EPA OPPTS 870.3650 under GLP conditions.

Based on the results of a 10-day dose range finding study, the dose levels for this study were selected to be 3, 10 and 30 mg/kg.

The test material, formulated in corn oil, was administered daily by oral gavage to SPF-bred Wistar Han rats. One control group and three treated groups were tested, each consisting of 10 males and 10 females. Males were exposed for 29 days, i.e. 2 weeks prior to mating, during mating, and up to termination. Females were exposed for 41 to 56 days, i.e. during 2 weeks prior to mating, during mating, during post-coitum, and during at least 4 days of lactation.

The following observations and examinations were evaluated: mortality / viability, clinical signs (daily), functional observations and locomotor activity (end of treatment), body weight and food consumption (at least at weekly intervals), clinical pathology (end of treatment), macroscopy at termination, organ weights and histopathology on a selection of tissues. Reproduction/developmental parameters were also evaluated.

Formulations were analysed once during the study to assess accuracy, homogeneity and stability. Analysis showed that the formulations were prepared accurately and homogenously, and were stable for at least 6 hours at room temperature.

Histopathological examination showed hepatocellular hypertrophy up to moderate degree in both sexes at 10 and 30 mg/kg. This was supported at necropsy by enlargement and/or accentuated lobular pattern of the liver for some animals at 30 mg/kg. At 30 mg/kg, hepatocellular necrosis was present in a single male and a single female at minimal degree. Additionally, higher liver weights (absolute and/or relative to body weights) were recorded at 10 and 30 mg/kg; relative liver weights were increased 39 and 63 % in males and females at 30 mg/kg, respectively, and 21 % in females at 10 mg/kg. The higher liver weights in females at 10 and 30 mg/kg along with the combined occurrence of hepatocellular hypertrophy with necrosis at 30 mg/kg were considered to be adverse in nature.

At 30 mg/kg, changes in blood of females that were considered to be related to treatment consisted of lower relative neutrophil counts, higher relative lymphocyte counts, lower mean corpuscular volume and mean corpuscular haemoglobin, higher total protein, albumin, calcium, cholesterol, potassium and glucose and lower urea and total bilirubin. Higher potassium and lower total bilirubin were also noted for males at 30 mg/kg.

Females at 10 and 30 mg/kg showed lower food consumption during the lactation period, as well as notable weight loss during lactation ranging from 4 to 9 % of Day 1 lactation values. The lower maternal food intake and body weight gain and mean pup body weight gain appeared unrelated on an individual animal basis. Also, these changes were not accompanied by supportive clinical signs or inadequate maternal care. As such, these changes in food intake and body weight gain during lactation were considered not adverse in nature.

No toxicologically relevant clinical signs or changes in functional observation parameters were noted.

No toxicologically relevant changes in reproduction parameters were observed up to the highest dose level tested (30 mg/kg). These parameters included mating, fertility and conception indices, pre-coital time, and numbers of corpora lutea and implantation sites, spermatogenic profiling, and histopathological examination of reproductive organs.

At 30 mg/kg, the mean number of living pups at first litter check appeared slightly lower than controls. Also, an increased postnatal loss and lower viability index was noted at 10 and 30 mg/kg. At 10 mg/kg, a total of 3 dams showed postnatal loss (1 dead or missing pup for two litters, and 6 missing pups for another litter). At 30 mg/kg, a total of 5 dams showed postnatal loss (1 missing pup for 3 litters, and 4 or 5 missing pups for two litters). The significance of these findings is not clear at this stage and are proposed to be further investigated

Mean pup body weights for both sexes combined on Day 4 of lactation were approximately 16 and 20 % lower than the control mean at 10 and 30 mg/kg, respectively. Although there were no other developmental changes noted for these pups (macroscopy and clinical signs), the magnitude of changes in pup body weight was considered to represent an adverse effect on pup development. No apparent relationship could be found between maternal food intake and mean pup body weight gain on an individual animal basis.

Mean male pup body weight was also lower at 3 mg/kg on Day 4 lactation (approximately 8 % lower than the control mean). Since this change in body weight was slight this was considered not to represent an adverse effect on pup development.

No treatment-related changes were noted in any of the remaining developmental parameters investigated in this study (i.e. gestation index and duration, parturition, maternal care and early postnatal pup development consisting of clinical signs and macroscopy).

Under the conditions of the study, the parental NOAEL was determined to be 3 mg/kg (based on higher liver weights at 10 and 30 mg/kg, with hepatocellular hypertrophy and necrosis at 30 mg/kg). The NOAEL for reproduction was determined to be at least 30 mg/kg.

In accordance with Section 8.7.3 of Column 2 of REACH Annex IX, it is considered justified to omit the extended one-generation reproductive toxicity study (EOGRTS) as it is not scientifically justified. Column 1 states that the EOGRTS should be proposed if the available repeated dose toxicity studies indicate adverse effects on reproductive organs or tissues or reveal other concerns in relation with reproductive toxicity.

The NOAEL established in the 2 year chronic study was 1.5 mg/kg bw/day and the material was determined to be non genotoxic. The repeated dose result was selected as the key value in the CSA and used to derive the DNEL for long term effects. The registrant considers it unlikely that any subsequent reproductive toxicity studies would result in a lower DNEL and it is considered that the one calculated on the basis of the chronic study will be suitably precautionary. Furthermore, an OECD 422 screening study showed no effects on reproductive parameters at the maximum dose level of 30 mg/kg bw/day.

Given that no reproductive effects were exhibited in the OECD 422 study and the chronic study, it is considered to be appropriate to omit the EOGRTS required in section 8.7.3 of Annex IX as it is considered to be unlikely that further information would be yielded by a new study.

Short description of key information:
ORAL
A combined repeated dose toxicity study with the reproduction/developmental toxicity screening test is available in which the NOAEL of the substance for reproduction was determined to be at least 30 mg/kg (the top dose tested) in male and female rats.

Justification for selection of Effect on fertility via oral route:
Only one study available.

Effects on developmental toxicity

Description of key information

ORAL
A combined repeated dose toxicity study with the reproduction/developmental toxicity screening test is available in which the NOAEL of the substance for developmental toxicity was determined to be 3 mg/kg in rats, based on lower pup body weight and increased postnatal loss at 10 and 30 mg/kg, and lower mean number of living pups at first litter check at 30 mg/kg.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

3 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The study was conducted in accordance with a standardised guideline under GLP conditions. It was awarded a reliability score of 1 in accordance with the criteria set forth by Klimisch et al. (1997). The quality of the database is therefore considered to be high.

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

The developmental toxicity of the test material was investigated in a combined repeated dose toxicity study with the reproduction / developmental toxicity screening test conducted in accordance with the standardised guidelines OECD 422 and US EPA OPPTS 870.3650 under GLP conditions.

Based on the results of a 10-day dose range finding study, the dose levels for this study were selected to be 3, 10 and 30 mg/kg.

The test material, formulated in corn oil, was administered daily by oral gavage to SPF-bred Wistar Han rats. One control group and three treated groups were tested, each consisting of 10 males and 10 females. Males were exposed for 29 days, i.e. 2 weeks prior to mating, during mating, and up to termination. Females were exposed for 41 to 56 days, i.e. during 2 weeks prior to mating, during mating, during post-coitum, and during at least 4 days of lactation.

The following observations and examinations were evaluated: mortality / viability, clinical signs (daily), functional observations and locomotor activity (end of treatment), body weight and food consumption (at least at weekly intervals), clinical pathology (end of treatment), macroscopy at termination, organ weights and histopathology on a selection of tissues. Reproduction/developmental parameters were also evaluated.

Formulations were analysed once during the study to assess accuracy, homogeneity and stability. Analysis showed that the formulations were prepared accurately and homogenously, and were stable for at least 6 hours at room temperature.

Histopathological examination showed hepatocellular hypertrophy up to moderate degree at 10 and 30 mg/kg. This was supported at necropsy by enlargement and/or accentuated lobular pattern of the liver for some animals at 30 mg/kg. At 30 mg/kg, hepatocellular necrosis was present in a single female at minimal degree. Additionally, higher liver weights (absolute and/or relative to body weights) were recorded at 10 and 30 mg/kg; relative liver weights were increased 63 % in females at 30 mg/kg, and 21 % in females at 10 mg/kg. The higher liver weights in females at 10 and 30 mg/kg along with the combined occurrence of hepatocellular hypertrophy with necrosis at 30 mg/kg were considered to be adverse in nature.

At 30 mg/kg, changes in blood of females that were considered to be related to treatment consisted of lower relative neutrophil counts, higher relative lymphocyte counts, lower mean corpuscular volume and mean corpuscular haemoglobin, higher total protein, albumin, calcium, cholesterol, potassium and glucose and lower urea and total bilirubin.

Females at 10 and 30 mg/kg showed lower food consumption during the lactation period, as well as notable weight loss during lactation ranging from 4 to 9 % of Day 1 lactation values. The lower maternal food intake and body weight gain and mean pup body weight gain appeared unrelated on an individual animal basis. Also, these changes were not accompanied by supportive clinical signs or inadequate maternal care. As such, these changes in food intake and body weight gain during lactation were considered not adverse in nature.

No toxicologically relevant clinical signs or changes in functional observation parameters were noted.

No toxicologically relevant changes in reproduction parameters were observed up to the highest dose level tested (30 mg/kg). These parameters included mating, fertility and conception indices, pre-coital time, and numbers of corpora lutea and implantation sites and histopathological examination of reproductive organs.

At 30 mg/kg, the mean number of living pups at first litter check appeared slightly lower than controls. Also, an increased postnatal loss and lower viability index was noted at 10 and 30 mg/kg. At 10 mg/kg, a total of 3 dams showed postnatal loss (1 dead or missing pup for two litters, and 6 missing pups for another litter). At 30 mg/kg, a total of 5 dams showed postnatal loss (1 missing pup for 3 litters, and 4 or 5 missing pups for two litters). The significance of these findings is not clear at this stage and are proposed to be further investigated. The registrant therefore proposes to conduct a full prenatal developmental toxicity study in rats in accordance to the OECD Guideline 414.

Mean pup body weights for both sexes combined on Day 4 of lactation were approximately 16 and 20 % lower than the control mean at 10 and 30 mg/kg, respectively. Although there were no other developmental changes noted for these pups (macroscopy and clinical signs), the magnitude of changes in pup body weight was considered to represent an adverse effect on pup development. No apparent relationship could be found between maternal food intake and mean pup body weight gain on an individual animal basis.

Mean male pup body weight was also lower at 3 mg/kg on Day 4 lactation (approximately 8 % lower than the control mean). Since this change in body weight was slight this was considered not to represent an adverse effect on pup development.

No treatment-related changes were noted in any of the remaining developmental parameters investigated in this study (i.e. gestation index and duration, parturition, maternal care and early postnatal pup development consisting of clinical signs and macroscopy).

Under the conditions of the study, the repeated dose NOAEL was determined to be 3 mg/kg (based on higher liver weights at 10 and 30 mg/kg, with hepatocellular hypertrophy and necrosis at 30 mg/kg). The developmental NOAEL was determined to be 3 mg/kg (based on lower pup body weight and increased postnatal loss at 10 and 30 mg/kg, and lower mean number of living pups at first litter check at 30 mg/kg).

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

Justification for classification or non-classification

N/A