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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

No toxicity observed even at highest concentration level tested.
Pseudokirchneriella subcapitata_OECD 201/EU Method C.3: ErC10(72h) > 100 mg/L WAF, ErC20(72h) > 100 mg/L WAF, ErC50(72h) > 100 mg/L WAF, EbC10(72h) > 100 mg/L WAF, EbC20(72h) > 100 mg/L, EbC50(72h) > 100 mg/L, NOELr(72h): 100 mg/L WAF, NOELb(72h): 100 mg/L WAF
RA_1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC)_Pseudokirchneriella subcapitata_ISO 8692: NOELr < 3.7 mg/L WAF, EL50 ~ 51 mg/L WAF
RA_1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC)_Desmodesmus subspicatus_OECD 201: EL10(72h) < 100 mg/L WAF, EL50(72h) < 100 mg/L WAF

Key value for chemical safety assessment

EC50 for freshwater algae:
100 mg/L
EC10 or NOEC for freshwater algae:
100 mg/L

Additional information

The acute toxicity of 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-nonanethiol (CAS 91648-65-6) towards Pseudokirchneriella subcapitata was investigated according to OECD Guideline 201 / EU Method C.3 under certificated GLP compliance (Vryenhoef, 2012). Pseudokrichneriella subcapitata is a freshwater unicellular alga, thus a representative of primary producers found in natural waters and can therefore be considered as an important non-target organism in freshwater ecosystems. Based on the results of a range-finding test (no effects at 10 and 100 mg/L WAF), the definitive test was conducted as "limit test" with a single loading rate of 100 mg/L to confirm that no effect on algal growth was observed. Six substance concentration and control replicates were prepared. Samples were taken at 0, 24, 48 and 72 h and the cell densities were determined using a Coulter(R) Multisizer Particle Counter. The pH was measured at the start and end of the test, the temperature was recorded daily. Potassium dichromate was used as reference substance, revealing an ErC50(72h) of 1.4 mg/L with 95 % CL of 1.2 - 1.7 mg/L and an EbC50(72h) of 0.59 mg/L of 0.53 - 0.65 mg/L. The NOEC was 0.25 mg/L and the LOEC was determined as 0.50 mg/L. At the start of the experiment all cultures were observed to be clear colorless solutions. After 72 h, the cultures were recorded as pale green dispersions. In the microscopic examination, neither globules nor micro-dispersions were present. The temperature was maintained at 24 +/- 1 °C throughout the test. The pH in the control cultures increased from pH 7.1 (0h) to 7.9 (72h). Differences between test and control groups were determined by Student´s t-test incorporating Bartlett´s test for homogeneity of variance (Sokal and Rohlf, 1981). Concerning growth rate, the ErC10(72h), ErC20(72h) and ErC50(72h) are reported as > 100 mg/L WAF in each case. The NOELr is reported as 100 mg/L WAF. Identical results are reported regarding yield inhibition. The level of the EC50 values are caused by the dose selection based on the limit test procedure.

The read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (No CAS, no EC) was also investigated for its toxicity towards Pseudokirchneriella subcapita (Bouillon, 2006). The test organisms were exposed at nominal concentrations of 0, 3,7, 14,8, 106, 1386 mg/L (WAF) under static conditions in accordance with ISO 8692. The NOELR and EL50 values based on biomass determination by absorption measurement (670 nm), resulting in values of < 3.7 mg/L WAF and approx. 51 mg/L WAF, respectively. The % growth inhibition in the treated algal culture as compared to the control ranged from 21% (3.7 mg/L) to 94 % (1386 mg/L). Neither the specific growth rate nor the mean coefficient of variation for section-by-section specific growth rates can be calculated for control cultures. Based on the insufficient documentation, reliability cannot be confirmed.

In another experiment, the freshwater algae species Desmodesmus subspicatus was also exposed towards the read-across substance 1,3,4-Thiadiazolidine-2,5-dithione, reaction products with hydrogen peroxide and tert-dodecanethiol (Weyandt and Lebertz, 2005). The test was performed according to OECD Guideline 201. The test was conducted as "limit test" with a single nominal substance concentration of 100 mg/L. The test solution was prepared as WAF by adding 125 mg of the test item to 1 L deionized water and shaking gently for 48 h. The suspension was filtered via a glass fiber filter and the pure eluate was used directly for testing without further dilution. The algal inocula for the experiment were taken from an exponentially-growing pre-culture and were mixed with the nutrient medium to make up to a final cell density of about 5000 cells/mL in the test medium. For the test item concentration as well as for the control 7 replicates were prepared, blind values were determined by 3 replicates without algae. During the test a temperature of 24 +/- 1 °C was maintained in the vessels under continuing illumination. The cell counts in all parallel cultures were determined photometrically after 24h, 48h and 72h. 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. Taking into account the water solubility of the test substance, the real values can be estimated as < 5mg/L. The specific growth rate and the mean coefficient of variation for section-by-section specific growth rates fulfill validity criteria, variation of average specific growth rates is not given. No analytical verification was performed, thus the obtained results are not taken into account for the risk assessment.