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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

72 hours of exposure to polysulfides, di-tert-dodecyl at its saturation concentration was found not to inhibit the growth of Pseudokirchnerilla subcapita, giving a NOEC of 0.08 mg/L (no LOEC observed). The 72hr NOELR was determined to be at least the limit of solubility of the nominal 100 mg/L concentration solution, though may lie above this value.

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Additional information

Thiebaud (2000) is a GLP-compliant guideline study showing the growth inhibition effect of polysulfides, di-tert-dodecyl on Pseudokirchnerilla subcapita over 72 hours. The maximum level of exposure, the saturation concentration (0.080 mg/L), resulted in no inhibition of the growth of Pseudokirchnerilla subcapita. The study is considered reliable and suitable for use for this endpoint.

This is supported by Hoffmann (2010), a GLP compliant, algae toxicity study following OECD guideline 201 and OECD guideline 23 on the testing of difficult substances. Due to the low water solubility of the substance, the test solutions use Water Accommodated Fractions, with no analytical monitoring, therefore only nominal concentrations are used. The only deviations to the study plan are the range in temperatures of the storage of the substance and this is not expected to affect the outcome of the experiment.

 

The OECD TG 201 (2010) study was conducted with WAFs ranging from 1 to 100 mg/L with a spacing factor of 3.2 (5 concentrations tested in triplicate). The study report clearly specifies that these “WAFs were prepared individually and not by serial dilution of the single stock solution”. Since 1 mg/L is 3846 times the water solubility limit of the registered substance (0.26 µg/L), it can be safely assumed that the 1 mg/L WAF was already a saturated solution of the registered substance. It comes that all the other concentrations tested were also saturated solutions of the registered substance.

The WAFs were allowed to settle for one hour and the test media were directly transferred from the bottles to the test flasks without any filtering or any other processing (e.g. centrifugation) before use. Therefore, it is excluded that the substance may have disappeared from the medium between preparation and use. It is clear that the algae were exposed to the test substance.

Moreover, as the substance is shown to be highly insoluble in water and is unlikely to cross the biological membrane (demonstrated by the results of the OECD TG 305 study as well as the high logkow (12.5 according to kowwin) this endpoint can be waived based on an adaptation of Annex VII, column 2 to Reach..