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Sediment toxicity

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Key value for chemical safety assessment

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Testing for toxicity to sediment organisms is not considered necessary because:

The hydrolysis half-life of the registration substance is approximately 43 hours at neutral pH. Given the residency time of the substance in the WWTP the long-term exposure is relevant for the hydrolysis product, therefore the hazard assessment for the sediment compartment is based on the silanol hydrolysis product.

In accordance with Column 2 of REACH Annex X, there is no need to further investigate the effects of the substance in a long-term sediment study because, as indicated in guidance R.7.11.6 (ECHA 2016), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1, and therefore the risk is already adequately controlled and further testing is not justifiable.

The silanol hydrolysis product is not readily biodegradable but has low potential for bioaccumulation and low bioavailability (based on log Kow <3 (0.9)), and there is no reason to expect any specific mechanism of toxicity beyond narcosis.

Long-term toxicity testing to aquatic invertebrates has been carried out with the registered substance as well as a structural analogue. During these tests, it is likely that organisms were exposed to the hydrolysis products of the test substance. The occurrence of more severe toxic effects in the terrestrial compartment that were not expressed in these aquatic studies (conducted at concentrations up to 100 mg/l) would be considered unlikely.

The PNEC calculated by Equilibrium Partitioning has been derived for the purpose of chemical safety assessment and the risk characterisation ratios are below 1.

Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further testing is not considered necessary.

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.