1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol

Endpoint summary

Additional information

General considerations

The ecotoxicological potential of 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) towards aquatic species was investigated in different experiments conducted with fish, daphnids and green algae to determine the toxicological effects in three different trophic levels. Further information is available from the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC), which was also investigated for its toxicity potential towards aquatic microorganisms. Both substances are UVCBs (Substances of Unknown or Variable composition, Complex reaction products or Biological materials). The difference is based on the diversity in the C-range of the used raw material: 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) requires a tert. C9 hydrogen sulphide and 1,3,4 -Thiadiazolidine-2,5 -dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) a tert. C12 hydrogen sulphide. Hence, due to the structural similarity of both substances it is obviously that the physico-chemical, toxicological and ecotoxicological properties are likely similar.

Based on the intrinsic properties of the used substances, Water Accommodated Fractions (WAFs) were prepared for testing. This procedure is in accordance with the OECD Guidance document on aquatic toxicity testing of difficult substances and mixtures (Series on testing and assessment - Number 23; OECD, 2000). The term WAF is applied to aqueous media containing only the fraction of multi-component substances that is dissolved and / or present as a stable dispersion or emulsion. These fractions are prepared individually and not by serial dilution of a single stock WAF. As the term indicates, only a fraction of the total mass of multi-component substances responsible for the composition may be present in the WAF. The "loading rate" is the mass to volume ratio of the mixture to medium used in the preparation. The obtained LL50/ EL50 values are comparable to LC50/ EC50 values, as well as the NOELR (No Observable Effect Loading Rate) to NOEL (No Observable Effect Concentration).

Toxicity to fish

Pimephales promelas was exposed to the target substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) in an experiment according to OECD Guideline 203 (McAllister, 1985). The LL50(96h) was determined to be > 1000 mg/L WAF. Hansonis-Jouleh (1993) investigated the toxicity of the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) towards Leuciscus idus melanotus. The study was also conducted according to OECD Guideline 203 and revealed a LL50(96h) of 1900 mg/L WAF. Based on these observations and the chemical safety assessment (CSA), no long-term studies with fish are triggered in accordance to REACH, Annex IX, Section 9.1.6, column 2.

Toxicity to aquatic invertebrates

1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) was found to be toxic against the freshwater invertebrate Daphnia magna in an experiment conducted according to OECD 202 (Vryenhoef, 2012). The EL50(48h) value was determined as 41 mg/L WAF.

Supporting data is given by the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) which was also exposed to Daphnia magna: In an experiment according to EU Method C.2 the available results were not suitable to calculate the EL50 exactly, thus it was estimated by the geometric mean (EL0/EL100), resulting in a value of 50 mg/L WAF (Caspers, 1999). Bouillon (2006) reported an EL50(48h) value of approx. 36 mg/L WAF (10 - 50 mg/L WAF) as result of an experiment conducted according to OECD 202/ISO 6341 15. In the last available study, which was also conducted according to OECD 202, an exact calculation of the EL50 value was not possible (Weyandt and Lebertz, 2005).

Taking into account these observations for the CSA, the target substance is classified as "Aquatic Chronic 3" (H412: Harmful to aquatic life with long lasting effects) and therefore, long-term toxicity investigations are waived in accordance to REACH, Annex IX, Section 9.1.5, column 2.

Toxicity towards aquatic algae

Vryenhoef (2012) exposed the green algae Pseudokirchneriella subcapitata towards the target substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) for a time duration of 72 h. The test procedure was in accordance to OECD Guideline 201/EU Method C.3 and up to the maximum concentration tested (100 mg/L WAF), no effects were observed. Based on growth rate as well as on biomass, the EC10, EC20 and EC50 values will be > 100 mg/L WAF. The corresponding NOELr and NOELb are 100 mg/L WAF both.

In another experiment with the same test organisms, the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) revealed an EL50 ~ 51 mg/L WAF (Bouillon, 2006). The study report describes that the test was conducted in accordance to ISO 8692, however, not all validity criteria were fulfilled. Neither the specific growth rate nor the mean coefficient of variation for section-by-section specific growth rates can be calculated for the control cultures since the coefficient of variation regarding the average specific growth rate in the replicate control cultures was > 7 %.

Weyandt and Lebertz (2005) exposed the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction product with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) towards Desmodesmus subspicatus in an experiment conducted in accordance to OECD Guideline 201. The cell reproduction inhibition and growth rate inhibition were determined after 72h as 80.1% and 52.4 % respectively. So the EL50 and EL10 values were determined to be < 100mg/L. The exact values could not be determined. However, no analytical verification was performed and no variation of average specific growth rates (validity criteria) is reported.

Toxicity towards aquatic microorganisms

Ecotoxicological data regarding toxicity towards aquatic microorganisms is only available for the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC). The substance was used in an experiment according to German standard DIN 38 412 (part 8) with Pseudomonas putida as test organism (Hansonis-Jouleh, 1993). After 16 h, the EC10 as well as the EC50 was determined to be > 8000 mg/L.

Toxicity towards other aquatic organisms

No information is available regarding toxicity towards any other aquatic organisms, neither for the target substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) nor for the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC). Based on the available data and the chemical safety assessment (CSA), no indication is shown to investigate further the fate and behaviour of the substances. Furthermore, it is no standard information requirement for a registration under REACH and thus no additional testing towards any other aquatic organisms is considered as necessary.