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Classification & Labelling & PBT assessment

PBT assessment

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PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB
Justification:

Biodegradation data shows tert-dodecanethiol not to be readily biodegradable in the aquatic environment (Jenkins, 1990) with an approximate half-life of 150 days when incubated in algal medium and pH 7 buffer solution under aerated conditions at 20 +/- 0.5°C (Sydney, 2006). Therefore, the substance is considered potentially persistent or very persistent in the environment.

The BCF of TDM has been determined using a number of different methods:

1.   Prediction from the BCF/BAF Arnot-Gobas model using a log Kow of 7.43 are 496, 688 and 760 L/Kg for TDM depending upon the trophic level of the fish used in the model.

2.   Prediction with the Gobas model and including the experimental TDM metabolism from the trout cell-line in vitro study,Cowan-Ellsberry et al.(2008), the BCF was predicted to be in a range from 594 to 867 L/Kg

3.   The experimentally derived BMF was measured in a study based on the OECD 305 draft protocol, 2010, Egeler and Gilberg (2012). The growth-corrected BMFK values are 0.00356 based on wet weight, and 0.00635 based on the mean lipid content as determined in fish and food which correlates with BCF values of 260 to 1246 when compared with other chemicals, where the BCF and BMF have been measured.

4.   Experimentally, in vivo with the BMF method including a transformation to BCF using allometric equations. As no single BCF value can be estimated a range of values is provided. The BCFs have been lipid normalised to 5% w/w as recommended by the OECD Guideline. Due to the difference in depuration rate equations, two sets of BCF have been highlighted depending on whether the 7 or 14 day depuration data are used (each based on six K1calculation methods):

a.  Lipid normalised BCF based on 7 day: mean = 1369.9 (with a range of approximately 1000 to 1950) and

b.  Lipid normalised BCF based on 14 day: mean = 2577.8 (with a range of approximately 1500 to 3650) depending on the method.

Given the concerns already expressed about these data, a weight of evidence approach leads to the conclusion that there is reasonable evidence the BCF of TDM lies between 500 and 1950 L/Kg.

The substance is not considered as B according to PBT criteria.

A total of 14 ecotoxicity studies have been evaluated (review by Thomas & Comber, 2013 attached) and are considered fit for use in hazard assessment; 9 aquatic acute studies, 2 ASRIT studies; 1 chronic study on daphnids; one sediment chronic test on chironomids and an earthworm reprotoxicity test.

Of these, due to methodological problems, only 5 of these studies were considered valid by the reviewers: The 2 ASRIT studies, one acute study on daphnids, the chronic daphnid study and the chronic sediment study. Nevertheless, several other studies were classified Klimisch 4 and can be used in a weight of evidence approach notably an acute study on trout and the chronic study on worms.

For aquatic acute or chronic studies, no effects were observed at concentrations at or cose to the solubility limit in any study.

The substance is considered non-Toxic according to PBT criteria.

 

Likely routes of exposure:

Generally, the environment is not expected to be exposed to the substance which is used mainly used as a chain transfert agent, fully consumend during the reaction. The substance is volatile and if waste streams are treated by industrial WWTPs sludges collected and destroyed, therefore not spread onto agricultural soil.