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In the 96-h acute toxicity study according to OECD 203 Oncorhynchus mykiss (rainbow trout) were exposed to bis(4-tert-butylcyclohexyl) peroxydicarbonate at nominal concentrations of 0 (control and solvent control), 100, 180, 320, 560 and 1000mg/L under semi-static conditions.

The 96-h LC50 was calculated to be 704 mg/L. The NOEC value, based on mortality, was 320 mg/L. As a sublethal effect, darkened pigmentation was observed in three fish exposed to 1000 mg/L test substance.

However, as undissolved test material was observed in the test vessels, which could have been ingested by the test fish, and since actual test substance concentrations were not analytically verified, the study is deemed to be unreliable.

Nevertheless, as fish is considered to be the least sensitive species, an additional vertebrate study for this endpoint was not commissioned.

In an OECD 202 guideline study the acute toxicity of bis(4-tert-butylcyclohexyl) peroxydicarbonate to Daphnia magna was investigated using 5 concentrations ranging between 460 and 10000 mg/L (nominal). For preparation of test solutions the test item was mixed with dilution water at a nominal loading of 10 g/L, followed by vigorous stirring at 37 ± 2 °C for 7 days. This procedure was chosen to maximise concentrations of the poorly soluble test material. The lower treatments were prepared by diluting with dilution water. Actual test concentrations of dissolved material (geometric means of 0-hour and 48-hour samples) were 8.9, 20.1, 43.1, 97.9, and 208.8 mg/L. Daphnia were exposed to the test item for 48 hours in a static test. The 48-h EC50 for bis(4-tert-butylcyclohexyl) peroxydicarbonate in Daphnia magna, based on geometric mean measured concentrations of the sum of the breakdown products cis- and trans-4-tert-butylcyclohexanol is 42 mg/L.

The 72-h toxicity of bis-(4-tert-butylcyclohexyl)-peroxydicarbonate against Desmodesmus subspicatus was determined according to OECD 201 resp. EU C.3. The main study was performed using five concentrations ranging from 10000 to 460 mg/L nominal concentration.

Test solutions were prepared analogue to the OECD 202 testing (see above). Actual test concentrations (geometric means of 0-hour and 72-hour samples), were determined by GC-measurement of the breakdown products cis- and trans-4-tert-butylcyclohexanol, (aggregate concentrations of parent substance including potentially formed hydrolysis products).The determination of the biological results was based on the geometric mean of the measured concentrations. The EC50 based on growth rate was determined to be 39 mg/L. The NOEC was determined to be 17 mg/L.

Tests regarding long-term toxicity to aquatic organisms (fish and invertebrates) were neither conducted nor is further testing proposed, for the following reasons: Fish are typically the least sensitive species with respect to toxicity of organic peroxides. Furthermore, this substance class generally shows a low acute/chronic ratio, allowing lowering of the default assessment factor from 1000 to 100 (see position paper attached to IUCLID section 13). Accordingly, significant reduction of uncertainty by conducting chronic aquatic toxicity tests is not expected. Performing long-term tests in fish and/or invertebrates is therefore considered to be unnecessary.

The results of the existing acute toxicity study in fish study are deemed adequate for classification purposes. The requirements for classification and labelling, i.e. availability of results for trophic levels, are fulfilled. The results on short-term toxicity in invertebrates and growth inhibition to aquatic plants are more sensitive compared to the acute toxicity in fish and are therefore critical for classification and labelling as well as for the risk assessment. Thus, particularly taking into account animal welfare considerations, a repeat study to obtain new data on the short-term toxicity on fish is deemed unnecessary.

In addition to the above reported results, the toxicity of the test item bis(4-tert-butylcyclohexyl) peroxydicarbonate to microorganisms was assessed in a five day bacterial inhibition assay using a design similar to the closed bottle test (OECD 301D) at nominal concentrations of 10 and 20 mg/L. Non-adapted activated sludge from a predominantly industrial sewage treatment plant served as inoculum. The presence of the test substance had no significant effect on the degradation of the reference substance sodium benzoate, indicating that it was not inhibitory. Therefore, the 5-d NOEC for toxicity to microorganisms is considered to be 20 mg/L.

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