6,6'-di-tert-butyl-2,2'-methylenedi-p-cresol

Carcinogenicity

Description of key information

No evidence of pre-neoplastic lesions nor neoplastic was found in a chronic (18 months) feeding study with male and female Wistar rats (Takagi 1994). However the study is reviewed as not qualified to be regarded as a carcinogenicity study; and thus no concluding conclusion could be reached. Nevertheless, the test substance 6,6'-di-tert-butyl-2,2'-methylenedi-p-cresol reveals no genotoxic activities in vitro.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Link to relevant study records

Reference

Endpoint:

carcinogenicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

acceptable, well-documented publication which meets basic scientific principles; however the study is reviewed as not qualified to be regarded as a carcinogenicity study (OECD SIDS 2003); ((limitations: no data to test substance homogeneity and stability given, small number of animals evaluated at study termination)

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

other: chronic oral toxicity study

GLP compliance:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

the animals were maintained at temperature of 24 +/- 1°C and 55 +/- 5% humidity with a 12 h light/dark cycle; rats were housed in plastic cages (5 rats/cage)

Route of administration:

oral: feed

Vehicle:

other: test substance contained in diet

Details on exposure:

pellets of diet containing the substance; stored at 4°C until use

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

18 months

Frequency of treatment:

daily

Post exposure period:

no

Remarks:

Doses / Concentrations:
0, 0.01%, 0.03%, 0.1%
Basis:
nominal in diet

No. of animals per sex per dose:

30 per dose and sex

Control animals:

yes

Details on study design:

Age at study initiation: 5 weeks old for both sexes; weight at study initiation: 393 +/- 21 g male, 230 +/- 15 g for female; no. of animals per sex and per dose: 30 (5 animals/group were sacrified after 6 and 12 months for hematological serum biochemical examinations)

Positive control:

no data

Observations and examinations performed and frequency:

Clinical observations performed and frequency: general conditions were observed daily; body weight and food consumption were determined monthly; hematological and serum biochemical examination were performed for 5 animals/sex/dose group at 6, 12, 18 months

Organs examined at necropsy:
Organ weight: brain, heart, lungs, liver, kidney, spleen, adrenals, testes, ovaries, pituitary and thyroid glands

Microscopic evaluation /all groups: brain, heart, lungs, liver, kidney, spleen, adrenals, testes, ovaries, pituitary and thyroid glands, salivary glands, esophagus, stomach, small and large intestine, pancreas, urinary bladder, seminal vesicles, epididymis, ischiac nerve, uterus, prostate, mesenteric lymph nodes, thymus, spinal cord, skeletal muscle, bone marrow

Sacrifice and pathology:

GROSS PATHOLOGY: Yes
HISTOPATHOLOGY: Yes

Statistics:

Analysis of variance (ANOVA) techniques with Dunnett's or Scheffe's test for continous data and Chi square test for analysis of categorical data

Dose descriptor:

NOAEL

Effect level:

12.7 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: slight increase in relative liver weights

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

LOAEL

Effect level:

42.3 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: decreased body weights, increased absolute and relative liver weights, decreased absolute and rel. testis weights, atrophy of testicular tubules and spermatogenic arrest and epididymis, hypospermia

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

NOAEL

Effect level:

15.1 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: no adverse effects

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

LOAEL

Effect level:

54.2 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: decreased body weights, increased absolute and relative liver weights

Remarks on result:

other: Effect type: toxicity (migrated information)

Dose descriptor:

NOAEL

Effect level:

42.3 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no interstitial cell tumors were apparent (no additional data given) (highest dose tested)

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

NOAELsystemic Male:300 ppm (12.7 mg/kg/day), Female: 300 ppm (15.1 mg/kg/day)

LOAEL systemic Male: 1000 ppm (42.3 mg/kg/day), Female: 1000 ppm (54.2 mg/kg/day)

Body weight: Significant suppression of body weight gain was observed from the month 6 in the male group at 1000 ppm and from the month 1 in the female group at 1000 ppm.

Food/water consumption: No significant effect was observed.

Table: effects seen after 18 months

	Males				Females
Diet level (ppm)	0	100	300	1000	0	100	300	1000
Final mean body weight (g)	545	528	520	498*	375	368	353	278*
Mean food intake (g/rat/day)	16.6	16.7	16.6	16.2	12.2	12.7	12.2	11.5

(* significant: not specified the degree)

Haematology: In the hematological and serum biochemical analysis, several parameters demonstrated significant alternation. However, none appeared to be of biological significance, since they did not show the same tendency throughout the experimental period and/or the degrees of change were very small.

Mortality and time to death: Survival rates in all treated groups were comparable to those of control.

Gross pathology incidence and severity: Organ weight changes:

Male: Increase in liver weight at 300 ppm (absolute (p<0.05) and relative (p<0.01)); decrease in testis weight at 1000 ppm (absolute and relative) (p<0.01)

Female: Increase in liver weight at 1000 ppm (relative) (p<0.01). no changes in ovary weights were observed in any of the treated females. no changes in other organs were observed in any treated groups for males and females.

Effects seen after 18 months

	Males			Females
Diet level (ppm)	0	300	1000	0	1000
Absolute weight
Liver (g, Mean ± SD)	12.28 ± 0.93	12.59	14.19 ± 1.35*	7.60 ± 0.88	7.39 ± 0.83
Testis (g, Mean ± SD)	3.28 ± 0.48		0.82 ± 10.18**
Relative weight
Liver (g%, Mean ± SD)	2.37 ± 0.16	2.58 ± 0.16**	3.00 ± 0.13**	2.08 ± 0.15	2.79 ± 0.35**
Testis (g%, Mean ± SD)	0.63 ± 0.10	0.82 ± 0.11	0.17 ± 0.05*

increase in rel. liver weight 109% compared to control, absolute liver weight increase: 103% compared to control

Histopathology (incidence and severity):

Histopathological lesions were only observed in the testis and epididymis of males.

However, no interstitial cell tumors were apparent (no additional data given). In the other organs of males, no changes induced by the test substance were observed and no changes in any organs were apparent in females. No neoplastic lesions which could be attributed to MBMBP were observed in any organs of males and females.

Male: Atrophy of testicular tubules and spermatogenic arrest and epididymis

hypospermia were observed in the 1000 ppm group.

Female: No significant effect was observed.

Table: Effects seen after 18 months

Diet level (ppm)	degree*	0	100	300	1000
No. of animals		19	19	18	19
Testis, tubules Atrophy	±	0	1	0	0
	+	0	0	0	0
	++	2	0	0	0
	+++	0	3	1	19
Spermatogenic arrest	++	2	0	0	0
	+++	0	1	1	19
Epididymis Hypospermia	++	2	0	0	0
	+++	0	1	1	19
interstitum
interstitial cell tumor		15	11	15	0
interstitial cell hyperplasia	+	3	7	2	0

CONCLUSIONS: Toxic effects in this study are suppression of body weight gain, increase in liver weight, decrease in testis weight, and histopathological lesions in the testis and the epididymis.

The NOAELs systemic are 12.7 mg/kg/day (300 ppm for male and 15.1 mg/kg/day (300 ppm) for female.

No interstitial cell tumors were apparent in any of the treated animals.

Executive summary:

No tumors were observed in a 18 -months chronic feeding study with rats up to 1000 ppm; however in the OECD SIDS (2003) the study is reviewed as not qualified to be regarded as a carcinogenicity study; and thus no conclusion could be reached on the carcinogenicity (OECD SIDS 2003).

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

42.3 mg/kg bw/day

Study duration:

chronic

Species:

rat

Carcinogenicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Carcinogenicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no study available

Justification for classification or non-classification

Classification is not required based on the classification criteria 67/548/EWG and regulation no. 1272/2008 (GHS).

Additional information

Carcinogenicity: oral

In a chronic feeding study (18 months) male and female Wistar rats were administered with 0, 100, 300 and 1000 ppm test substance 6,6’-di-tert-butyl-2,2’-methylendi-p-cresol in the diet (more more details see chapter repeated dose toxicity). No signs of toxicity were indicated related to test substance treatment. In addition, survival rats of treated rats were comparable to control animals. A suppression of the body weight gain was noted at 1000 ppm (corresponding to 42.3 mg/kg bw/d for males and 54.2 mg/kg bw/d for females). An increase in the relative liver weight was found at 300 ppm and 1000 ppm for males and 1000 ppm for females. In males a decrease of the absolute and relative testes weights and atrophy of testicular tubules were observed at 1000 ppm. In addition a spermatogenic arrest and epididymis hypospermia were noted at this concentration. No neoplastic lesion attributable to the substance was observed in any organs evaluated of either sex. The NOAELs for systemic effects are considered to be 12.7 mg/kg/day (300 ppm) for male and 15.1 mg/kg/day (300 ppm) for female (Takagi 1994).

In conclusion, no evidence of pre-neoplastic lesions or neoplastic lesions was found in a chronic (18 months) feeding study with male and female Wistar rats (Takagi 1994). However in the OECD SIDS (2003) the study is reviewed as not qualified to be regarded as a carcinogenicity study; and thus no concluding conclusion could be reached