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Ecotoxicological information

Short-term toxicity to aquatic invertebrates

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Description of key information

- OECD 202 (Daphnia magna): EL50(48h): 41 mg/L WAF with 95 % confidence limits of 39 - 43 mg/L WAF (read-across from supporting substance '1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol) 
- OECD 202/ISO 6341 15 (Daphnia magna): EL50(48h): 10 - 50 mg/L WAF (nominal), approx. 36 mg/L WAF (nominal)
- EU Method C.2 (Daphnia magna): available results are not suitable to calculate the EL50, so it was estimated by the geometric mean EL0/EL100 = 50mg/L WAF (nominal)
- OECD 202 (Daphnia magna): limit test, a calculation of the EL50 was not possible EL50(48h) < 100 mg/L WAF

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
41 mg/L

Additional information

The acute toxicity of the supporting substance ‘1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol’ (CAS 91648-65-6) towards Daphnia magna was investigated according to OECD 202 / EU Method C.2 under certificated GLP compliance. Daphnia magna is a freshwater representative of a wide variety of natural habitats and can therefore be considered as an important non-target organism in freshwater ecosystems. Based on the poor water solubility of the test substance (< 0.1 mg/L at 20°C), a modification of the standard method for the preparation of aqueous media was performed. Using the approach of Water Accommodated Fractions (WAFs), based upon an approach by several important regulatory authorities in the EU and elsewhere, aqueous media are prepared by mixing the test substance with water for a prolonged period. Pre-study work showed that a preparation period of 24 hours was sufficient to ensure equilibration between the test substance and the water phase. After a 1-hour settlement period, the test substance is phase separated by siphon and the test organisms exposed to the aqueous phase or WAF. Following a preliminary range-finding test, twenty daphnids (4 replicates of 5 animals) were exposed to the WAFs over a range of nominal loading rates of 10, 18, 32, 56 and 100 mg/L for 48 h at a temperature of 21 - 22 °C under static test conditions. The number of immobilised Daphnia and any adverse reactions to exposure were recorded after 24 and 48 hours. The water temperature was recorded daily, dissolved oxygen concentration and pH were recorded at the start and termination of the experiment. Immobilization of daphnids was observed after 24 h and 48 h. After an exposure period of 24 h 50 % of daphnids were immobilized at 56 mg/L WAF. Therefore, the EL50(24h) is reported as 56 mg/L. After 48 h, all daphnids were immobilized at 56 mg/L WAF. Based on statistical interpolation, the EL50(48h) is determined as 41 mg/L with 95 % confidence limits of 39 - 43 mg/L WAF. The LOELR(48h) was considered to be 56 mg/L WAF and the NOELR(48h) is 32 mg/L WAF.

Finally, it is considered justified to use the results of the short-chain homolgue ‘1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol’ for the target substance ‘1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol’.

However, study results are also available for the target substance '1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol' that confirm the received result of the afore-mentioned (key) study on the supporting substance:

On the one hand the 48h-acute toxicity of '1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol' to Daphnia magna was studied under static conditions. Daphnids were exposed to control and test chemical at nominal concentration of 12.5, 48.6, 171 and 1486 mg/L WAF for 48h. Immobilisation was observed daily. The 48h-EL50 was determined to be 10-50 mg/L WAF (nominal), thus approx. 36 mg/L WAF (nominal).

On the other hand the acute toxicity to aquatic invertebrates of ‘1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol’ was investigated according EU Method C.2 with GLP compliance. Young daphnids (Daphnia magna) were used as test organisms. The exposure time lasts for 48 hours in a static mode. The photoperiod was chosen as 16 h light and 8 h dark. Considering the heterogenous composition of the test substance, Water Accommodated Fractions (WAFs) were prepared. No analysis was included. Physico-chemical parameters were measured after 24 and 48 hours. The EC0 and EC100 values were determined directly from the study, while the EC50 was calculated from the dose-response curve obtained. The resulting data of the mobility investigations of Daphnia magna were not suitable to calculate the EL50, so it was estimated by the geometric mean EL0/EL100 = 50mg/L. 

Finally, Daphnia magna were also exposed to '1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol' in a static limit test conducted in accordance to OECD 202. The nominal test concentration was 100 mg/L, whereby the solution was prepared as Water Accommodated Fraction (WAF). The percentage of immoblised daphnids was 75 % after 24 h and 100 % after 48 h, respectively. Therefore, the EC0(48h) as well as the EC50(48h) is < 100 mg/L WAF, whereas the EC100(48h) is > 100 mg/L WAF (nominal, no analytical measurements were performed).