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Ecotoxicological information

Long-term toxicity to fish

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Description of key information

90 d NOEC ≥14 μg/L, measured, Oncorhynchus mykiss (Springborn Smithers 2009f). This is above the water solubility of the registration substance D6 (5.1 µg/L); therefore, D6 is not expected to show toxicity at its limit of solubility.

Key value for chemical safety assessment

Additional information

Reliable test results are available for long-term toxicity to fish. A 90-day Read-Across NOEC of ≥14 µg/L has been determined for the effects of the supporting substance decamethylcyclopentasiloxane (D5) on hatching and larval survival and growth ofOncorhynchus mykiss. The results were obtained from an early-life stage: reproduction, (sub)lethal effects flow-through test, conducted in accordance with OECD Guideline 210 (Springborn Smithers 2009f). The read-across justification is discussed in the Ecotoxicological Information endpoint summary.

This is supported by a 49-day NOEC of >4.4 μg/l for the effects of the registration substance, D6, on mortality of adult fish (Pimephales promelas). No other effects were assessed in this test, which was primarily designed to study bioconcentration.

A reliable QSAR method indicates that no effects are expected at the limit of solubility in test media for D6. This is a qualitative conclusion based on the high value of log Kow. The method has been validated for use with cylic volatile methyl siloxanes such as D6 and works well (see QMRF attached to the IUCLID 5 dataset; Peter Fisk Associates 2013bc).

The conclusion of no effects at the limit of solubility is further supported by a peer-reviewed study by Redman et al (Redman 2012). A tissue based risk assessment was performed, with measured tissue concentrations of D4, D5 and D6 compounds in fish and benthic invertebrates compared with critical target lipid body burdens (CTLBBs) as estimated with the target lipid model (TLM). Acute and chronic toxicity data for these compounds were compared with data for nonpolar organic chemicals to validate application of the TLM in this effort. The analysis was extended to estimate the contribution from metabolites to the overall tissue residues using a food chain model calibrated to laboratory and field data. Concentrations of the compounds in biota from several trophic levels, including fish, are well below the estimated CTLBBs associated with acute and chronic effects. The data support the use of the TLM model (which assumes a non-polar narcosis mode of action) for D4, D5 and D6 and demonstrate their generally low bioavailability.

The impacts of any uncertainty in the conclusions regarding chronic effects on fish on the chemical safety assessment are discussed in Section 10 of the CSR.