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

Endpoint summary

Additional information

It should be noted that the test substance is not considered as posing a hazard to the environment.

The test substance, Thanox 1520, is a liquid under all environmental conditions and is of low solubility in water. It has a low volatility (based on a ≤ 1 Pa at 25 Deg C) and a low affinity for soil / sediment value of Koc 99 (from an OECD 106 soil adsorption study). As such, any environmental release will result in virtually all of the substance compartmentalising into water compartments, with little release directly to atmosphere or compartmentalising to soil/sediment compartments.

Any potential exposure to the environment is predicted to result in redistribution to both water and soil; however due to its low volatility, low water solubility and partitioning values, these indicate that the majority of the substance would eventually partition to water rather than to soil and sediment should it be released to the environment. 

A Level III fugacity model was conducted in the US EPA EPISUITE (Mackay,) which assumes steady-state but not equilibrium conditions. The Level III model in EPI Suite predicts partitioning between air, soil, sediment and water using a combination of default parameters and various input parameters. This model has been used to calculate the theoretical distribution of the highest % component substance between four environmental compartments (air, water, soil, sediment) at steady state in a unit world.

 Partitioning is detailed to be:

-        Air        0.214%

-        Water     16%

-        Soil       59.9%

-        Sediment  23.9%

It is proposed that although the majority of the substance is modelled to distribute to the soil and sediment compartments within the model, the low soil adsorption instead indicates that the substance is more likely to distribute between water (e. g. soil pore water) and soil. The substance displays a low ready biodegradability in that it achieved 4% biodegradation in a 28-day ready biodegradation study, indicating that it is unlikely to achieve a half life of less than 40 or 60 days within fresh water attributed to ready biodegradation alone. However it is expected to hydrolyse slowly under normal environmental conditions.  Experimental studies on hydrolytic effects demonstrated that the substance does undergo hydrolysis at environmentally relevant pH’s, with a half life of 5.8days at pH 4 and 13.1 days at pH 9. As such, degradation is anticipated via this route. Studies on direct phototransformation in water are not available but it is assumed on the basis of chemical structure and nature of use that the substance is not degraded by direct photolysis. It is concluded, therefore, that abiotic processes would contribute significantly to the depletion of the substance within the environment. 

The substance has been demonstrated to have a very high partition coefficient value which demonstrates that the potential for this substance to accumulate biologically is negligible, given that it is a high value of 10 by calculation. The calculated high log Pow is considered to be more a consequence of poor water solubility issues than a lipophilic tendency and is considered to be not indicative of the tendency to bioaccumulate in lipid tissues of aquatic organisms. This is based on literature data which demonstrates a tendency for the Bioconcentration Factor (BCF) to decrease as Log Pow increases above 6. At a high value of 10, the substance is proposed not to bioaccumulate.  This is further confirmed via the use of QSAR; use of the EU CAESAR programme for bioaccumulation indicates that the substance is unlikely to bioaccumulate, with values of

BCF value:6 (L/Kg) whole body weight

Log BCF value:0.76

Given the fact that the substance is subject to hydrolysis at biologically relevant pH’s (4 and 9), it is anticipated that bioaccumulation of the substance itself would not occur, as hydrolytic effects in association with metabolic effects would result in removal of the substance. These factors indicate that bioaccumulation within body tissues is unlikely. 

Adsorption to soil is deemed to be low, based on the low soil adsorption coefficient value. Such a low potential indicates that the substance is unlikely to bind tightly to soils and sediments and instead partition instead to water. As such, significant exposure related effects to sediment and soil dwelling organisms are considered to be negligible.

Based on its low water solubility, high partition coefficient and fairly rapid hydrolysis rate at environmentally relevant pH’s, it can be concluded that it is unlikely that Thanox 1520 could potentially be persistent within the environment. Abiotic effects within the environment will result in eventual removal from the environment and hence significant contact with the organisms in the food chain can considered to be minimised. 

Finally, Thanox 1520 demonstrates low acute toxicity in mammalian studies therefore in the event of exposure to environmental organisms, effects due to secondary poisoning can be excluded.

Reliability.

The studies have all been ranked reliability 1 according to the Klimish et al system. This ranking was deemed appropriate because the studies were all conducted to GLP in compliance with recognised guidelines.

Justification for classification or non classification

The above results triggered no classification under the Dangerous Substance Directive (67/548/EEC) and the CLP Regulation (EC No 1272/2008).