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Toxicity to microorganisms

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Description of key information

DOTTG is manufactured as a 2.5 -10 % solution in DOTE/DOTI

So the predominat exposure of microorganisms, will be to DOTE or it's degradation products DOTO and EHTG

The corresponding degradation products of DOTTG would be DOTO and Thioglycolic acid.

Studies done on different organotincompounds with thioligand at higher pH demonstrate the stability during manufacturing process, which includes contact to water and to simulate the exposure and behavior in the environment.

Dioctyltins with a thio ligand hydrolyse in acetonitrile/water solutions to form dioctyltin oxide and release the thioligand

The formation of the ligand EHTG could be observed unequivocally, whereas the formation of DOTO was postulated. The DOTO signal intensity remained constant in the experiment, which was attributed to the very low solubility of DOTO. (Yoder 2003)

The study shows, that dioctyltins in solution react rapidly with water to form Dioctyltin oxide and the ligand. The scenario is relevant for any dissolved dialkyltin compounds which are dissolved in water, e.g. during sewage treatment.

So both the study on DOTE as well as on DOTO are considered relevant for the assessment of the toxicity to microorganisms

Roulstone (2012), OECD 209 (read-across from dioctyltin oxide); EC50 > 1000 mg/L, NOEC 1000 mg/L.

Baumann (1992), Directive 87/302/EEC, part C (read across from DOTE) EC50 >= 100 mg/L

The ligand which is released during hydrolysis of dialkyltin thioglycolates (Yoder 2003) is Ethylhexyl thioglycolate (EHTG)

It is is self-classified as Aquatic Acute 1 and Aquatic Chronic 1.

The ligand of DOTTG, Thioglycolic acid is not classified for the environment and thus does not pose any additional risk for the environment when released from DOTTG by hydrolysis

It degrades in water by fast oxidation to dithiodiglycolate.

Based on the physico-chemical properties of thioglycolic acid and salts (high solubility and low Log P), it is considered that they are not expected to adsorb to suspended solids, sediments and soils and are mobile in soil

Thioglycolic acid and its main oxidation product, the diammonium dithiodiglycolate, it can be considered that thioglycolic acid and its salts are ready biodegradable and do not raise concern in terms of persistency.

Thioglycolic acid and its salts are highly soluble in water (> 1000 g/L at 20°C) (Sablowski, 2007b; reliability 2) and have a partition coefficient octanol-water equal to -2.99 at 22°C and pH 7. Therefore thioglycolic acid is not expected to bioaccumulate according to technical guidance documents

RAC (RAC 47, November 2018) came to an opinion that DOTE fulfils the CLP criteria for classification as Aquatic Acute 1 and Aquatic Chronic 1.

Since DOTTG is manufactured only in 2.5-10 % in DOTE this opinion ios relavant for the classifcation of DOTTG.

The RAC opinon on the aquatic classification of DOTE has been adopted for DOTTG.

Any different result of a study on pure DOTTG would not change the adopted classifcation of the manufactured and marketed form of DOTTG

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 ng/L
EC10 or NOEC for microorganisms:
1 000 mg/L

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