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Ecotoxicological information

Short-term toxicity to fish

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Description of key information

A 96-h LL50 of >100 mg/l and a NOELR of ≥100 mg/l (highest concentration tested) have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss based on nominal concentrations, in accordance with test guideline OECD 203.

Key value for chemical safety assessment

Additional information

A 96-h LL50 >100 mg/L, and NOELR >= 100 mg/l, have been determined for the test substance based on mortality of Oncorhynchus mykiss. The fish were exposed to a filtered suspension of the test substance prepared at a loading rate of 100 mg/l. The loading rate of 100 mg/l was far above the water solubility of the substance (<0.1 mg/l). Results of a related study conducted under the same project number but with unfiltered test media resulted in mortalities of the test organisms that were attributed to the effects of the undissolved test substance. A parallel exposure to a 100 mg/l test medium that had been filtered gave a similar result to that reported in this study (96-h LL50 >100 mg/l).

Based on the hydrolysis half-life of the test substance (43 hours at pH 7 and 20-25°C, predicted), it is likely that in the absence of undissolved material the organisms could be exposed to a mixture of the parent and the hydrolysis products. Undissolved material might have been present in the test solutions as film on the surface or as hydrolysis resistant micelles of the parent substance and oligomers in the water body. The observations during the tests with fish, Daphnia and algae indicate that the dosage of the test item and the filtration step are hypersensitive parameters for the occurrence of undissolved material. A filter is not able to retain effectively undissolved monomers and oligomers.

The results are supported by a reliable study with the read-across substance triethoxyoctylsilane. The test substance did not achieve any toxicity when tested at the solubility limit of the substance i.e. the 96-h LC50 value was >0.13 mg a.i./l and the NOEC value was ≥0.13 mg a.i./l (nominal concentration).

Refer to the discussion in the Section 6 endpoint summary (Section 7.0 of CSR) for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.