2,2-dioctyl-1,3,2-oxathiastannolan-5-one

Long-term toxicity to fish

Description of key information

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.

Aquatic acute

The opinion is based and an EC50 of 24.12 mg/L reported for Daphnia Magna. this value lies above the threshold for an aquatic acute classification. However, this value is higher than the maximum water solubility of 0.001 pg/L reported in the CLH report for DOTE. According to the Guidance on the Application of the CLP criteria (p561 version 5.0 – July 2017) “where the acute toxicity is recorded at levels in excess of the water solubility, the L(E)C50 for classification purposes may be considered to be equal to or below the measured water solubility. In such circumstances it is likely that category Chronic 1 and/or category Acute 1 should be applied.

Aquatic Chronic

The key value is a NOEC of 0.286 mg/L for Daphnia magna. On the basis of this, RAC concluded that DOTE fulfils the CLP criteria for classification as Aquatic Chronic 1

 

Impurities

Commercially marketed octyltin stabilizer systems contain (besides DOTTG) EHTG as impurity .

The current self classification for EHTG in the REACH dossier is Aquatic Acute 1 and Aquatic Chronic 1 with M-factors of one. For any available form of DOTE with EHTG as impurity at levels of 0.1% and higher, this would also result in the same classification.

 

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

Exposure considerations:

DOTTG is manufactured and marketed as constituent (2-10 %) in DOTE / DOTI. Although manufactured intentionally in situ in DOTE/DOTI solution the character is comparable to an impurity relevant for classification

Thus the dominant exposure of the environment will be to DOTE / DOTI and valid studies on DOTE and it's hydrolysis product DOTO describe the aquatic toxicity.  

 

Whereas EHTG, the ligand of DOTE, which will be released during hydrolysis (Yoder 2003) 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 an 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

 

The negligible exposure of the environment is based on the following:

·        Waste water treatment

·        Complete transformation of DOTTG during manufacturing of PVC articles

·        Results of screening studies

Treatment of wastewaters from manufacturing of organotin compounds

All wastewaters having contact to organotin substances are treated in the following way:

1) De-tinning

The waste water is treated with iron trichloride, which forms cloudy suspended particles. Organotins, which are known for there high affinity to solid materials adsorb to the Iron trichlorie. The solid material is precipitated and incinerated in a industrial waste incineration plant.

 

2) Biological STP

The remaining water phase is treated in an onsite industrial two step biological waste water treatment plant with de-nitrification and final flotation.

Suspended matter is thus removed in two steps.

The total effluent volume is 63000 m³

The average (3years) tin content of the wastewater after de-tinnin is 194 mg/l

The average (3years) tin content of the effluent is 0.06 mg/l = 0.06 g/m³

The latter value – including the analytical method – is requested and monitored by the local environmental authority.

The analyses are approved by the authorities and conducted in a third party authorized laboratory

Estimate of total emissions:

Tin content is used here as an analyzable sum parameter and reflect all tin substances handled in manufacturing which have contact to water.

The portion of tin in water originating from DOTTG based on a 3 years average product mix is 0.0058

Based on this a 3 years average yearly emission of tin originating from DOTTG can be estimated to be:

63000 m³ x 0.06 g/m³ x 0.0058 = 21.9 g [Sn]

In a worst case that DOTTG would not degrade at all during waste water treatment the total yearly emission can be estimated to be: 21.9 g [Sn] / 0.26 % Sn in DOTTG = 95.7 g [DOTTG]

The effluent from waste water treatment is entered into the river Rhine. A screening study from the German BFR did not find octyltin compounds in Mussels as test organism in the river Rhine.

 

Potential Exposure of the environment via service life of articles containing DOTTG:

 

It has been demonstrated in a study on PVC foils, that DOTTG is completely used up during the stabilization process in the manufacturing of PVC articles.

So an exposure via PVC articles can be excluded.

 

Screening Studies:

Numerous studies which have been conducted analyzing organotins in the environment and in humans with high fish consumption support the negligible abundance of octyltin compounds in general in the aquatic environment.and food chain.

 

The studies cover different aquatic compartments like lakes, rivers, sea, harbours, municipal STPs, sediment. The investigated biota vary from algae, via crustea to fish. The geographic areas covered are Scandinavia, Baltic States, Germany, Serbia and India.

 

Whereas in most of the studies Tributytin- and Triphenyltin compounds are detected, mono- and dioctyltin compounds have been found only in small concentrations, close to the detection limit in the water of Indian harbours and in the influent of Swedisch sewage treatment plants.

No octyltin compound have been found in any study in sediment, algae, crustea or fish.

Blood analyses from fishermen and family members support the findings in the environment.

Since DOTTC is only present in Octyltinstabilizers in minor amounts of 2.5-10 %) and transformed completely during the manufacturing of plastic articles it can be assumed that none of the analysed octyltin is DOTTG.