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Screening Assessment and Testing Strategy for octamethylcyclotetrasiloxane (D4, CAS 556 -67 -2)

The registration substance, D4, falls within soil hazard category 3 as defined in REACH R.7; high absorption (log Kow>5) but no indication that the substance is very toxic to aquatic organisms.

An OECD TG 216 soil microorganism has been conducted with the registration substance in accordance with ECHA decision number TPE-D-2114422498-44-01/F. An OECD TG 222 earthworm reproduction test is also required and is currently in progress; the earthworm study has been delayed due to difficulties encountered with survival of earthworm populations (under control and test conditions). Until the results of the OECD 222 earthworm study are available, the chemical safety assessment cannot be finalised and PNECs cannot be derived from test data with the registration substance. The need for further terrestrial toxicity tests (OECD TG 208) will also be reviewed once the results of the OECD 222 study are available.

The OECD 222 study is expected to commence in September 2021, once a new worm population has been age-synchronised at the test facility.

Interim approach to terrestrial hazard assessment

Until these data become available, PNECsoil has been calculated from PNECfreshwater on the basis of the equilibrium partitioning method (EPM), using aquatic toxicity data for D4. Effects were seen during the aquatic tests with D4, whereas no effects were seen in terrestrial tests with D5. Therefore, deriving the PNECsoil for D4 based on EPM represents a worst case, as soil toxicity data are available for D5 which indicate that EPM could be over-precautionary.