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

Toxicity to aquatic algae and cyanobacteria

Description of key information

DOTTG is manufactured and marketed as constituent (2-10 %) in DOTE / DOTI. Although manufactured intetionally 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

 

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.

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 aqiatic classification of DOTE has been adopted for DOTTG

 

Although exposure based waiving is not forseen for this endpoint the following considerations should not remain unmentioned

 

 

The exposure of the environment is unlikely due to the following reasons:

 

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 matter. 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) 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]

 

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.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 ng/L

EC10 or NOEC for freshwater algae:

0.001 mg/L

Additional information

The key study provided to fulfil the data requirement, Rufli (1988b), was conducted to the standardised guideline OECD 201 using the read across substance, dioctyltin oxide. The study lacked details in the reporting in some areas and some deficiencies were present in the performance of the test, such as the test concentrations were not maintained throughout the entire test period. As such the study was assigned a reliability score of 2 in line with the principles of assigning data quality as outlined in Klimisch (1997). The study was considered reliable with restrictions and suitable for assessment. Under the conditions of the study, the ErC50 of the test material in algae was determined to be greater than the water solubility of the test material.