Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

No test data are available with tetradecamethylhexasiloxane (L6, CAS 107-52-8).

 

Testing for toxicity to terrestrial organisms with soil micro-organisms and a stability test under OECD 222 (earthworm reproduction test) conditions have been carried out with Octamethyltrisiloxane (L3, CAS 107-51-7), and an integrated test strategy of soil stability and ecotoxicity testing in accordance with standard guidelines is planned for several structurally analogous siloxanes, members of the same analogue group as L6.

 

The tests with L3 have demonstrated that there was significant loss of test item from the test system, very early on during the tests, even though efforts had been taken to minimise losses through volatility. The studies indicate that L3 is too volatile to maintain adequate concentrations in the test system.

The high Henry's Law Constant of L6 indicates that similar experimental difficulties would be expected if terrestrial tests were attempted with L6. This conclusion will be revisited in future when the currently ongoing studies with other siloxanes are complete.

In the interim, the approach described below has been applied.

Tetradecamethylhexasiloxane (CAS 107-52-8) is a member of the 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.

The registrant 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. Testing for toxicity to terrestrial organisms (earthworm reproduction test, OECD 222; terrestrial plant test, OECD 208) is proposed for the related test substance dodecamethylpentasiloxane (L5, CAS 141-63-9), pending demonstration of adequate stability in the test soil.

Effects on soil microorganisms are not anticipated. In aquatic toxicity testing, activated sludge (sewage treatment plant micro-organisms) do not appear to be affected by siloxanes. However, some further testing with soil-specific species (again, subject to demonstration of adequate stability in the test system) is considered to be useful as further validation. Toxicity to soil microorganisms studies are planned for the related test substance dodecamethylpentasiloxane (L5, CAS 141-63-9, EC 205-492-2). The registrant plans to read across the results of this study to the registration substance. Should no toxicity be observed in studies with D5 (CAS 541-02-6) and another analogue group member, L3 (CAS 107-51-7), no further microbial assays with siloxanes will be proposed.

The approach will be reconsidered once the relevant stability and toxicity studies are complete.

The registrant plans to read across the results of the earthworm reproduction test and terrestrial plant test with L5 to the registration substance.

The testing endpoints and methods are discussed further in PFA 2014i.

Until these data become available, there are no unacceptable risks for the soil compartment.

PNECsoilfor the registration substance has been derived based on read across from D5, which has similar physicochemical properties to L6; the risk characterisation ratio (RCR) based on PNECsoilis <1.

Justification for planned and interim read-across is given in Section 7.0.The read-across is considered to be reliability 2 and the data are considered to be suitable for deriving an interim PNECsoilfor the registered substance.The testing with D5 has been carried out with species that are representative of three taxonomic groups; earthworms, springtails and plants.

·        A 28-day LC50value 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 LC50value of 813 mg/kg dry weight and a 28 day IC50value 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 IC50value 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/EC50values 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 EC50values 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.The registered substance and the surrogate substance share similar physicochemical properties but are not close structural analogues (linear and cyclic siloxanes respectively).However the studies are considered to be suitable to derive an interim hazard and risk assessment under REACH.