Di-tert-butyl trisulphide

Endpoint summary

Additional information

Experimental results were identified for the three trophic levels. The toxicity to micro-organisms has been taken from the inhibition control of a ready biodegradability test.

Thiebaud (2000) is a 48 -hour, static, freshwater, GLP-compliant study on Daphnia magna with analytical monitoring, following OECD 202. A 100 mg/L stock solution in the medium was prepared by intense stirring at 30°C during 4 hour then 20°C during 62 hours. The report states that the medium is cloudy, contains droplets and has an oily film on the surface. Consequently the solution is filtered under pressure through a PVDF filter with pore size 0.22µm. The resulting clear solution is the stock solution for experiments. Dilutions of this solution in the test medium are prepared between 50 and 13.5 mg/L (after a range-finder). Test flasks are penicillum type of 120 mL, completely filled and tightly closed (clinched). Measurement of concentrations at t=0 and t=48h show a very good recovery (final/initial > 90%). The highest test concentration is measured to be 0.27 mg/L (it represents 50% of the saturated solution, indicating a solubility in the test medium of about 0.54 mg/L). A concentration/effect relationship is observed, and it is possible to conclude on an EC50-48h = 0.24 mg/L

This study has no significant drawback apart from the fact that some dilutions are below analytical limit of quantification. Consequently it is considered reliable and rated as Klimisch 1. It is the key study for this end point and will drive the aquatic acute toxicity classification as well as the PNECs calculation as it is the most sensitive trophic level.The EC50 result for aquatic invertebrates of 0.24 mg/l indicates that polysulfides, di-tert-butyl is very toxic to aquatic invertebrates.

The toxicity of polysulfides, di-tert-butyl to fish has been assessed by Kley and Wydra (2010). The test is a GLP-compliant study following OECD 203 guideline. Based on the test results the 96 -hour LC₅₀of Polysulfides, di-tert-Bu for Zebrafish(Danio rerio)was determined to be higher than 0.24 mg test item/L based on the nominal test concentration. Based on the mean measured concentration of the test item the 96-hour LC₅₀was determined to be higher than 0.088 mg/L.This fish acute toxicity study has been run at only one concentration with the aim to check the relative sensitivity of fish compared to invertebrates (daphnia) where an EC50-48h = 0.24 mg/L had been obtained (see above). The laboratory prepared a solution at a nominal concentration of 0.24 mg/L by dissolving 2.4 µl of test item in 10 L of test water, followed by intense stirring for 2 min, just before introducing fish. This procedure looks not very robust given the very large dilution and the short homogeneisation period. The report states nevertheless that a static design was chosen due to preliminary non GLP (and not reported) experiments showing stability of TPS44 in the medium. Unfortunately the test failed to confirm this, as only 29% recovery was obtained at t=0 and 41% at t=96h. It is important to state that no mortality was observed, nor any sublethal effect. The report provides LC50 and NOECs being higher than nominal concentration 0.24 mg/L of arithmetic mean of initial and final measured concentrations i.e. 0.088 mg/L.

Overall, this study looks flawed (one more demonstration that the label GLP is not always a guarantee). Given the uncertainty on design and analytics it is not possible to draw a quantitative conclusion on acute toxicity of TPS 44 towards fish but qualitatively it can be assumed that no acute toxicity to fish is observed from exposure at concentration in water causing 50% immobilisation of daphnia. It is not proposed to launch another acute fish toxicity test as invertebrates look more sensitive.

The toxicity of polysulfides, di-tert-butyl to algae has also been assessed by Kley (2010). The test is a GLP-compliant guideline study showing the growth inhibition effect of polysulfides, di-tert-bu on Pseudokirchnerilla subcapita over 72 hours. The biomass, growth rate and yield 72 hour NOEC was 0.1 mg/L for nominal concentration and 0.04 mg/L for geometric mean concentrations. The 72 hour EC50 for nominal concentrations was 2.45 mg/L for growth rate. The 72 hour EC50 for geometric mean was 0.838 mg/L for growth rate. The study is considered reliable and suitable for use for this endpoint.

PNECaqua has been derived using the above mentioned data. Calculations of the risk ratio PEC/PNECaqua for the different emission scenarios show a large margin of safety, so it is not proposed to refine PNECaqua through chronic toxicity studies on pelagic species.