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Reliable short-term toxicity tests results are available for freshwater fish (Cyprinus carpio), invertebrates (Daphnia magna) and algae (Scenedesmus subspicatus) for [2-(perfluorohexyl)ethyl]triethoxysilane (CAS 51851-37-7). The relevant short-term values are:

Fish: LC50 (96 h): >3.1 mg/L; NOEC: ≥3.1 mg/L (highest concentration tested)

Daphnia: EC50 (48 h): >9 mg/L; NOEC: ≥9 mg/L (highest concentration tested)

Algae: EC50 (72 h): >7.1 mg/L; NOEC: ≥7.1 mg/L (highest concentration tested)

 

Test solution preparation for the fish, invertebrate and algal tests involved making a stock solution and stirring this for 18 hours prior to adding the test organisms. The pH during the fish test was measured as 8.5 to 9, during the invertebrate test as 7.9 to 8.0 and the pH at the start of the algae test was 7.6 to 8.0. By the end of the algae test the pH had risen to 9.4 to 9.6. [2-(Perfluorohexyl)ethyl]triethoxysilane will hydrolyse in water under dilute conditions (half-life rates have been measured at 20°C as 1.44 hours at pH 4, 12.5 hours at pH 7 and 5.18 hours at pH 9). Given that the rate of hydrolysis is expected to be slowest at around pH 7 and increase as the pH is raised or lowered, it is possible that pH could influence the exposure of the organisms to [2-(perfluorohexyl)ethyl]triethoxysilane and its hydrolysis product, [2-(perfluorohexyl)ethyl]silanetriol. However, due to the hydrolysis rate of 12.5 hours at pH 7 and the fact that the very low water solubility of the parent substance can limit hydrolysis, the chemical safety assessment is based on the properties of the parent substance. The amount of silanol present in the test solution is dependent on how much of the parent substance was dissolved. The water solubility of the parent is extremely low and the test results show values above the limit of solubility. Measurements of test substance in solution were made by dissolved organic carbon analysis (DOC). With DOC it is not possible to differentiate dissolved forms of the test substance and it is therefore unclear how much of the parent substance, silanol hydrolysis product or oligomer were dissolved in the test solution. However, there were no effects seen during the tests and so it can be concluded that no effects were seen at the limit of solubility of the test substance.

The presence of fluorocarbon chains means that the parent substance, silanol and condensation products have the potential for some surface activity. This is proven for the silanol based on measured and read-across data. The effective limits of solubility of both the parent substance and monomeric silanol hydrolysis products are very low because of the tendency to condense to oligomers which are of very low solubility. All forms of the substance may have a tendency to enrich at surfaces rather than forming stable evenly dispersed solutions. These phenomena may limit the extent of hydrolysis under conditions at which the solubility of either parent or oligomer is exceeded. The substance is extremely difficult to test and so best use has been made of the existing studies.

Refer to IUCLID Section 6 endpoint summary (CSR Section 7.0) for further discussion of the approach to chemical safety assessment.