Dodecamethylcyclohexasiloxane

Endpoint summary

Additional information

This registration substance is a member of an analogue group of siloxanes. In view of the high potential to adsorb to soil and the potential persistence in soil for siloxane substances, and the lack of terrestrial toxicity testing across the analogue group, it is concluded that further testing is required. An integrated terrestrial toxicity testing strategy for the analogue group is proposed to validate the use of read-across (or equilibrium partitioning) within the analogue group. Reconsile plans to carry out stability tests, replicating the testing conditions of standard OECD studies, prior to conducting the OECD soil toxicity testing studies. The soil toxicity studies will only be carried out if stability studies show that it is possible to maintain appropriate concentrations of the test substance in the test medium over the duration of the study.

Reliable terrestrial data are available for the siloxane D5 (CAS 541-02-6) and are read-across to D6. The testing has been carried out with species that are representative of three taxonomic groups; earthworms, springtails and plants.

A 28-day LC50 value of >4074 mg/kg dry weight and a 56-day NOEC of ≥4074 mg/kg dry weight have been determined for the effects of the test substance on mortality and reproduction and growth respectively of the earthworm, Eisenia andrei.

A 28-day LC50 value of 813 mg/kg dry weight and a 28 day IC50 value of 767 mg/kg dry weight have been determined for the effects of the test substance on mortality and reproduction of the springtail, Folsomia candida. A NOEC of 377 mg/kg dry weight has been determined by the reviewer on the basis of a visual examination of the data for both mortality and reproduction.

A 14-day IC50 value of 209 mg/kg dry weight has been determined for the effects of the test substance on root dry mass of Barley,Hordeum vulgare. IC50/EC50 values for effects on seedling emergence, root and shoot length and shoot dry mass determined in the same test were ≥248 mg/kg dry weight. 14-day EC50 values of >4054 mg/kg dry weight have been determined for the effects of the test substance on seedling emergence, root and shoot length and root and shoot dry mass of Red Clover, Trifolium pratense. NOECs were not determined in the tests.

The D5 terrestrial studies are considered to be non-standard; they have been conducted by spiking surrogate biosolids mixed into natural soil rather than by direct spiking of soil.

It is not necessary to base a PNECsoil on these data as the PNEC derived for the registered substance by equilibrium partitioning is considerably lower and is therefore appropriately protective for use in the chemical safety assessment.

Further information is given in a supporting report (PFA, 2015i) attached in Section 13 of the IUCLID 5 dossier.