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The results for the ecotoxicity of polysulfide di-tert-nonyl have been read across from polysulfide di-tert-dodecyl. These substances are polysulfides, characterised by hydrocarbon compounds containing one or more groups of atoms of the element sulphur linked together by covalent bonds. Given that the partition coefficient for the two substances is very similar, with polysufide di-tert-nonyl having a log Kow of >5.2 and polysulfide di-tert-dodecyl having a log Kow of >6.2, it is expected that the substances would behave similarly in the aquatic environment. The size and structure of the substances are very similar and therefore the substances are expected to have similar ecotoxicological properties and read across between the substances is considered to be justified.

The toxicity of polysulfide di-tert-nonyl to zebrafish (Danio rerio) has been read across from polysulfide di-tert-dodecyl, based on the loading rate, gives a 96-hour LL50 of >100 mg/L, a NOEC of <100 mg/L and a LOEC of 100 mg/L. Hoffmann (2010) is a GLP-compliant, static closed vessel limit test following OECD guideline 203. No further dose-response test was performed despite the limit test showing toxic effects, as the concentration tested was the threshold concentration and the highest concentration at which substances need to be tested. No further information would have been gained about the toxicity of the test item from further dose-response testing. There are considered to be significant methodological deficiencies with the study. Based on recent water solubility testing that has been conducted, the test item has a solubility of 0.26 µg/L. The method used for preparing the test solutions means that droplets may be present in the water column, and as no analytical monitoring was conducted the concentrations cannot be verified. The study is therefore considered to be unreliable, and chronic test results are used to assess toxicity to fish instead.

A second acute fish study is available for polysulfide di-tert-nonyl, which shows the substance is not toxic to the fish Brachydanio rerio when the fish are exposed for 96 hours at the saturation limit. The concentration of the test substance in the saturated solutions could not be determined as it was below the limit of analysis (0.11 mg/L). Thiebaud (2000) is a GLP-compliant study following OECD 203 guidelines. The concentration of the substance in the solutions could not be determined as the water solubility limit was below the limit of analytical detection. However, the substance was found not to be toxic at 0.11 mg/L, the limit of solubility.

Although there is some variation in the values obtained for the toxicity to fish for polysulfide di-tert-nonyl and that read across from polysulfide di-tert-dodecyl, the conclusion reached for both studies indicates that polysulfide di-tert-nonyl has an LC50 above its limit of solubility. The value for the toxicity to fish in Thiebaud (2000) is similar to the results for toxicity to invertebrates and algae read across from polysulfide di-tert-dodecyl and again it is concluded that the substance has L/EC50s above its limit of water solubility. Therefore, given the similar results for each trophic level and the L/EC50s above the limit of solubility for each species tested, read across between the substances is considered to be justified.

The toxicity of polysulfide di-tert-nonyl to aquatic invertebrates has been read across from polysulfide di-tert-dodecyl. At the solubility limit, no significant effect was observed after 48 hours and so the EC50 was determined to be >0.1 mg/L, the limit of quantification of the analytical technique. Thiebaud (1998) is a 48 hour, static, freshwater, GLP-compliant test on Daphnia magna, following EU Method C2. The results indicate that this substance EC50 is above the limits of solubility. The validity criteria of the method were not met as the stability of the substance was not checked but the study is considered suitable for use for this endpoint.

The toxicity of polysulfide di-tert-nonyl to algae was tested in a 72-hour, GLP-compliant study conducted according to OECD 201. No toxicity was observed on the growth rate of the freshwater alga, Pseudokirchneriella subcapitata, giving EL50, EL10and NOELR values of >0.78, >0.78 and ≥0.78 µg/L, respectively. Due to the low water solubility of the test substance, the test solutions were prepared as Water Accommodated Fractions (WAFs).

Two chronic studies are available, conducted with polysulfide, di-tert-dodecyl. Migchielsen (2016a and b) assessedchronic toxicity of the substance in fish and Daphnia magna, respectively. Both studies followed standard OECD guidelines (OECD 210 and OECD 211) and used a single test concentration slightly above the saturation limit of the test item (nominally 1.3 µg/L), using acetone as a solvent.This equated to an average measured concentration of 0.84 µg/L in the fish study and 0.79 µg/L in the Daphnia study(measured using UPLC-MS/MS). In the fish study, Pimephales promelas were used, and a semi-static study was conducted over an exposure period of 32 days.The endpoints assessed were embryonic development, survival and hatching, larval survival and development and effects on larval growth, and no biologically significant effects were observed in the study.In the Daphnia study, effects on reproduction were assessed over 21 days in a semi-static study. No biologically significant effects were observed over the course of the study at the limit test concentration.Both chronic ecotoxicity studies followed standard guidelines and used test methods suitable for the poorly soluble test item, they are therefore considered to be reliable without restrictions. 

The toxicity of polysulfide di-tert-nonyl to micro-organisms has been read across from polysulfide di-tert-dodecyl. Hervouet (1989) is 16 hour, freshwater study on Pseudomonas putida following the method ISO/TC 147/SC 5 WG 1(N111). Due to the low solubility of the substance, several solutions were prepared, with the No Effect Concentrations ranging from 10mg/L (solvent added) to 10000 mg/L (ultrasonic method). Direct addition of polysulfide di-tert-dodecyl in the GST middle culture did not determine an inhibitory effect up to a dose of 10 g/L but found that bacterial growth was superior to that of controls.

Based on the dataset available, it can be concluded that polysulfides, di-tert-nonyl is not toxic at the limit of solubility. Chronic ecotoxocity studies with fish and Daphnia magna showed no biologically significant effects at the solubility limit. No environmental classification is therefore required for this substance.