Phenol, 2,4-bis[(dodecylthio)methyl]-6-methyl-

Endpoint summary

Description of key information

28 day subacute study: NOAEL = NOEL = 1000 mg/kg bw; CIBA 2003, OECD Guideline Study. 
In addition, the following information is available for the C8 analogue: In a  90-day oral gvage toxicity study conducted in dogs (CIT, 884345, 1991) according to the OECD Guideline 409, a dose level up to 1000 mg/kg caused weak effects on liver enzymes and biliary cell proliferation possibly indicating advere effects on liver. No effects were observed at 10 mg/kg bw.  

Additional information

In 28 day subacute toxicity study (CIBA 844256, 2003), the test substance was administered daily by oral gavage to SPF-bred Wistar rats of both sexes at dose levels of 50, 250 and 1000 mg/kg body weight/day for a period of 28 days. A control group was treated similarly with the vehicle, polyethylene glycol 300, only. The groups comprised 5 animals per sex which were sacrificed after 28 days of treatment. Additional 5 rats per sex and group were used at 0 and 1000 mg/kg. These animals were treated for 28 days and then allowed a 14-day treatment-free recovery period after which they were sacrificed. Clinical signs, outside cage observation, food consumption and body weights were recorded periodically during pretest, the treatment and recovery periods. Functional observational battery, locomotor activity and grip strength were performed during week 4. At the end of the dosing and the treatment-free recovery period, blood samples were withdrawn for hematology and plasma chemistry analyses. Urine samples were collected for urinalyses. All animals were killed, necropsied and examined. Histological examinations were performed on organs and tissues from all control and high dose animals, and all gross lesions from all animals. Oral administration of the test item to Wistar rats for 28 days resulted in no effects upon mortality, clinical signs (daily, weekly), functional observational battery including grip strength and locomotor activity, mean food consumption, mean body weights, mean organ weights, parameters of hematology, clinical biochemistry and urinalysis, and macroscopic or microscopic findings. Based on the results of this study, 1000 mg/kg body weight/day of the test substance was established as the no-observed-effect-level (NOEL) and as the no-observed-adverseeffect-level (NOAEL).

For other endpoints, read-across to 4,6-bis(octylthiomethyl)-o-cresol is applied. A data matrix with a separate justification is attached to the Chemical Safety report.

The read-across substance differs in the length of the alkyl chain at the thio ether. Specifically, it is a C8 chain in comparison to a C12 chain in the target substance. Due to the shorter chain length, the molecule is smaller and predicted to be of slightly better solubility in water. Therefore, it is considered to be of better systemic availability which might result in a slightly higher toxicity compared to the target substance. As both C8 and C12 chains are metabolized via beta oxidation, both substances are predicted to have the same metabolites. Overall read-across is justified.

For the read-across substance, two 90 -day studies are available which show that the dog is more sensitive than rats. A NOEL of 10 mg/kg bw was determined, due to liver biliary cell proliferation at 100 and 1000 mg/kg bw. The findings itself are not as hazardous as to trigger a classification for repeated-dose toxicity, but they result in a lower DNEL as that would be derived from the 28 -day study with the target substance.

1) Rat study with the C-analogue:

In a CIT (1989) study conducted according to the OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity in Rodents), three groups of Sprague-Dawley rats received by gavage the test substance at the 10, 100 and 1000 mg/kg/day dose levels. Each group contained 10 males and 10 females except the 0 (vehicle only and acted as control) and 1000 mg/kg/day groups which contained each 20 males and 20 females. After a 91-days treatment period, the first 10 males and females of the control and high dose level groups were kept for a 28-day recovery period. The other animals were sacrificed after a 92 or 93-day treatment period for necropsy. The dose selection was based on the results of 28-days OECD Guideline 407 study in rats (Ciba Geigy, 1988), where treatment with the test item at 10, 50, 250 and 1000 mg/kg/day dose levels resulted in functional adaptations, including slightly increased liver weights in males treated at 250 and 1000 mg/kg and in females treated at 1000 mg/kg correlated with minimally increased activity of alkaline phosphatase (with no histopathological changes).

The results of the 90-days study can be summarized as follows:

- Hyper-salivation after treatment observed in 6/20 males and 6/20 females of the 1000 mg/kg/day group. This clinical sign was considered treatment related.

- Mortality was detected in 1/20 males (5%) in the control group and 1/10 males (10%) and 1/10 females (10%) in the 100 mg/kg/day group. But, in the absence of dose-relationship, the mortality rate is not considered to be of toxicological significance.

- While the bodyweight gain in all treated females and in males of the 10 and 100 mg/kg/day groups was similar to that of the control animals, a very slight increase in the bodyweight gain (related to an increase of the same intensity in the food consumption) was noted in the males of the 1000 mg/kg/day group. Throughout the recovery period, the reversibility of the increase in food consumption was assessed but the difference in bodyweight was still observed. Although these changes were very slight, the relationship to the treatment cannot be ruled out.

- No drug-related abnormality was detected in ophthalmological examinations, and no change of toxicological significance was observed in the hematological and blood biochemical parameters, as well as at the urinalysis.

- A slight increase in the net and/or relative liver weight was found in the females of the 100 mg/kg/day group and in the animals of the 1000 mg/kg/ day group. But in the absence of abnormalities at the macroscopic and microscopic examinations, this change was considered to be of no toxicological significance.

- No changes of a toxicological significance were observed at the macroscopic and microscopic examinations.

In conclusion, the administration of the test substance by gavage to the rat for a 90-day period, at the dose levels of 10, 100 and 1000 mg/kg/day induced hyper-salivation in some animals of the high dose level and a very slight increase in the bodyweight gain related to an increase of the same intensity in the food consumption. Throughout the recovery period, the reversibility of the increase in food consumption was assessed but the difference in bodyweight was still noted. No other change with a toxicological significance was observed. Thus, the high dose level of 1000 mg/kg/day was well-tolerated and considered as NOAEL.

 

2) Beagle dog study with the C8 analogue:

In a CIT (1991) study conducted according to the OECD Guideline 409 (Repeated Dose 90-Day Oral Toxicity in Non-Rodents), groups of 6 (high dose group) and 4 (low and mid dose treatment) male and female Beagle dogs received the test substance by oral administration (gavage) at dosages of 10, 100, or 1000 mg/kg daily in a total volume of 2 ml/kg over a period of 13 weeks followed by a 4 week recovery period. The dose selection was based on the results of a 14-days range-finding toxicity study (CIT, 1989) where no systemic adverse effect was observed at 2000 mg/kg/day during. A control group of further 6 dogs received the vehicle (0.3% carboxymethylcellulose and 0.1% Tween 80 in water). Two males and 2 females of the control and high dose groups were kept for a 4-week recovery period after the termination of the treatment. At the end of the treatment and recovery periods, the animals were sacrificed and the results of the study can be summarized as follows:

- There were no clinical signs which might be related to the treatment with the test substance and no deaths occurred throughout the study.

- At the dose level of 1000 mg/kg/day slight decreases in body weight were observed in 2 males and one female, from week 1 to week 5 for one male and from week 6 or 7 to week 10 for the other animals. 

- A moderate increase in neutrophils was observed in a few males and females of the 1000 mg/kg/day on weeks 4, 8 and 13. Evidence of reversibility was found after the 4-week recovery period.

- A slight to moderate increase in aminotransferase and/or alkaline phosphatase activities was observed in a few males and females from the 100 and 1000 mg/kg/day groups on weeks 4, 8 and 13. These changes were dose-related and evidence of reversibility was found after the 4-week recovery period.

- No abnormalities in organ weights related to the treatment were observed. No macroscopic abnormalities of toxicological significance were found.

- A slight to moderate biliary cell proliferation was found in 3 males and 3 females of the 100 mg/kg/day group and in 3 males and 2 females of the 1000 mg/kg/day group. Biliary cell proliferation is generally a process that reverses slowly, and accordingly, it was at the end of the 4 -week recovery period.

The liver was considered as the target organ in beagle dogs, and the dose level of 10 mg/kg/day as the No Observable Effect Level (NOEL) under the conditions of the study.

Justification for classification or non-classification

Based on the OECD criteria for repeated dose toxicity, there is no need for classification of the test substance for repeated dose toxicity according to the EU Dangerous Substance Directive 67/548/EEC and to the CLP Regulation (EU) 1272/2008 as amended for the second time in Directive EC 286/2011.