2,4,6,8,10-pentamethylcyclopentasiloxane

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

fish early-life stage toxicity

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Additional information

Due to the rapid hydrolysis of the substance, the chemical safely assessment is based on the silanol hydrolysis product methylsilanetriol.

Testing for long-term toxicity to fish is not considered necessary because:

- The substance is highly water-soluble, has low bioavailability (based on log K_ow <3 (-2.4 at 20°C, QSAR)) and there is no reason to expect any specific mechanism of toxicity beyond narcosis. Therefore, the occurrence of toxic effects that were not expressed in the existing short-term aquatic studies, read across from a structural analogue with the same silanol hydrolysis product, would be considered unlikely.

- Based on the short-term aquatic data set, no effects were seen in any trophic level. Long-term testing with methylsilanetriol has been carried out with Daphnia at concentrations up to 10 mg/l. No effects were observed. An algal NOEC of ≥500 mg/l has also been determined, which is equivalent to ≥264 mg/l when expressed in terms of the hydrolysis product, methylsilanetriol.

- The hydrolysis product of the registration substance and the substances used for read-across are part of a class of low functionality compounds acting via a non-polar narcosis mechanism of toxicity, and as such log K_ow drives toxicity. It is therefore expected that fish will not be any more sensitive than invertebrates or algae. As no long-term toxic effects were expressed in these organisms, or short-term effects in any of the test organisms, a long-term fish toxicity test is not necessary.

- Aquatic PNECs have not been derived due to the high water solubility and low log K_ow of the registration substance, and absence of effects when structural analogues have been tested at high concentrations. Overall it is concluded that no hazard is identified and therefore further in vivo testing is not considered necessary or justified on ethical grounds.  

Details on PNEC derivation and risk can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.

In addition, the substance is only used in industrial settings in closed systems under controlled conditions and emissions to surface waters are unlikely. Therefore, further studies are not scientifically justified.