A mixture of: α-3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionyl-ω-hydroxypoly(oxyethylene); α-3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionyl-ω-3-(3-(2H-benzotriazol-2-yl)-5-tert-butyl-4-hydroxyphenyl)propionyloxypoly(oxyethylene)

Endpoint summary

Description of key information

Short description of key information on bioaccumulation potential result: 
Toxicokinetic and metabolism data using phenolic ring-U-14C-labelled test material is available for the analogue methyl ester.   No bioaccumulation potential is derived from this data.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

The substance consists of multiple components that can be assigned into three groups. Group one consists of monoesters of polyethylene glycol and 3-[3-tert-butyl-5-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]propionic acid. Group two consists of diesters of polyethylene glycol and 3-[3-tert-butyl-5-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]propionic acid and group three of PEG 300.

This mixture is surface-active and the more insoluble diester components are dispersed via the monoesters and free PEG 300.

A representative monoester and diester component with n=6 (PEG monomer) were synthesized to allow determination of water solubility and log P_OW. For the monoester component, water solubility was 1.7 mg/L and log P_OWwas 5.9 (HPLC-method). For the diester component, water solubility is less than 0.2 mg/L and log P_OWis 4.6 (HPLC-method).

The log POW values are above four and might give rise of concern for bioaccumulation. However, esters are susceptible to enzymatic hydrolysis. In this case, experimental data is available for the analogue methylester (CAS 84268-33-7). Toxicokinetic and metabolism data using phenolic ring-U-14C-labelled test material is available for the analogue methyl ester (RCC project no. 904098, reported 1992 and Ciba-Geigy project no CB 91/02, reported 1991). The methylester is of lower molecular weight and may therefore be more easily cleaved than the ester group in the test item. However, the data shows that in principle this ester bond is susceptible to enzymatic hydrolysis. For the methyl ester, most radioactivity was excreted with the feces within the first 24 hours, whereas 4- 5 % were eliminated in the urine. Elimination was efficient and almost complete after 168 hours. In vitro studies with the analogue methylester showed that both 1 % rat serum and 1.25 % rat liver homogenate readily hydrolyzed the ester bond at neutral pH with hydrolysis half-times of 14 and 37 minutes, respectively. Slower turnover was observed with small intestine homogenate.

Systemic uptake and an adaptive response of the liver are obvious from the repeated-dose toxicity studies and the mechanistic investigations with the substance itself. Peroxisome proliferation was demonstrated. Effects on liver were reversible during the four-week recovery period of the subchronic toxicity study (CIT 1988).

Peroxisome proliferation was also reported for the methyl ester and for 3-[3-tert-butyl-5-(2H-benzotriazol-2-yl)-4-hydroxyphenyl]propionic acid itself (Ciba-Geigy 1989).

Based on the reversibility of liver effects and ester hydrolysis, the substance is not expected to have a potential for bioaccumulation.