4,6-bis(octylthiomethyl)-o-cresol

Endpoint summary

Description of key information

Not readily biodegradable (according to OECD criteria) in screening tests according to OECD 301 guidelines. In a study according to OECD TG 308, neither the parent substance nor any of the identified metabolites exceeded the P criteria in freshwater (40 days) or sediment (120 days) according to Annex XIII of the REACH regulation in both test systems.

Thus, the substance is regarded as not P/vP.

Additional information

The substance was assessed to be not readily biodegradable according to a OECD TG 301 B study (BASF 1987). Thus, and due to the substance properties, and study according to OECD TG 308 has been performed (BASF 2021).

The results of the study showed that the behaviour of the registered substance in the water/sediment systems is characterized by moderate degradation in water phase and sediment compartment.

Mass balance: Sum of the activity in the water phase, trapped 14CO2 in 1 M NaOH and organic volatiles in ethylene glycol traps and inorganic other volatiles in H2SO4 traps, sediment wet extracts, soil residue on combustion and washed fractions. The mass balance in both systems TS1 and TS2 on the first day of exposure (Day 0) lies within a range of 90-110% TAR, respectively 96.7% and 95.5%. Recovery at Day 0 ranged from 95.4% to 97.9% (single values) and in TS2 from 94.3% to 96.7% (single values). An average of 90.6% TAR recovery in TS1 was observed (after removing the outlier on Day 85 in TA14 from the calculation where a 60% recovery due to a significant 14CO2 loss). In TS2, on the other hand an average of 86.5% TAR recovery was observed after excluding the outlier on Day 8 (TA21) from the calculation where only 69.3% was recovered due to possible low substance application.

Dissipation: A distinct and continuous decrease of the activity in the water phase and an increase in sediment bound activity during the whole exposure period was observed in both water/sediment systems. The dissipation in TS2 was very faster and by Day 22, only 13.1%TAR was remaining in the water phase. In the system TS1, it took around 49 days to decrease the radioactivity to 12.8% TAR in contrary to Day 22 in TS2.

Volatiles 14CO2: Carbon dioxide evolution steadily increased from both test systems throughout the incubation. Mean 14CO2 evolved at end of study in Ranschgraben was 44.0% (44.4% max at Day 100; replicate 2) and Berghäuser Altrhein was 18.6% (19.2% max at Day 100; replicate 1).

Other volatiles: No organic or other inorganic volatile compounds were evolved throughout incubation (< 0.0% of applied activity in both test systems).

Extractable and bound residues: Extractable residues in sediment declined with time in both test systems which is the sum of % TAR obtained in all solvent extractions. Recovery at Day 0 was 4% and 1.3% (mean) in TS1 and TS2 respectively and correspondingly the mean total extractable residues at the end of study was 6.7% and 10.6%.

Bound residues: Bound residues (NER, after total combustion) increased throughout the incubation period in both systems and reached maximum around 49.6% in TS1 and 62.4% in TS2, which is the radioactivity in the sediment measured by total combustion after the wet extraction using methanol. However, by the end of exposure, around 8-10% decrease from these peak values in the bound residues were observed in both TS1 and TS2.

Mean bound residues at day 0 in Ranschgraben: 1.4%; Berghäuser Altrhein: 1.5%

Mean bound residues at end of study Ranschgraben: 40.7% (49.6% max at Day 63); Berghäuser Altrhein: 50.4% (62.4% max at Day 49)

Degradation of parent led to speciation of the bound activity into fulvic acids (14.1%), humic acids (5.5%), and non-soluble humins (8.2%) in TS1 as mean values on Day 100. In the TS2, the major activity was found in humins (27.7%) and fulvic acids (6.4%), and minor activity was found in humic acids (5.5%).

The biomass and the other parameters measured in the control at the end of exposure showed that the systems were stable and active during the exposure time. No inhibition effect to microorganism in the test vessels were found in the inhibition test vessels.

Based on these results, degradation half-lives (DegT50/90) for the whole system in TS1 and TS2, the dissipation half-lives DT50 and DT90 of parent and metabolites in whole system, water and sediment were calculated without a GLP status using CAKE. Dissipation half-lives of parent (P-I level) and major metabolites such as Met 1.7 min, Met 2.2 min, Met 2.78 min, Met 6.6 min, Met 10.18 min, Met 16.5 min and minor metabolite at Met 5.8 min at M-I level were assessed and a summary of best fit with DT50 and DT90 given below (IUCLID Chapter 5.2.2). For the rest of metabolites, kinetics assessments were not performed due to not enough data points or due to the absence in the compartments. The DegT50/90 values in whole system for parent and metabolites such as Met 1.7 min (C1), Met 2.78 min (B1), and Met 16.5 min (A1), Met 10.18 min (A2), Met 6.6 min (B2), and Met 5.8 min (A3) at P-I level were calculated by SFO model and the results are also given in IUCLID Chapter 5.2.2.