3,3-bis[(dimethylvinylsilyl)oxy]-1,1,5,5-tetramethyl-1,5-divinyltrisiloxane

Endpoint summary

Additional information

An OECD TG 222 earthworm reproduction test is available for the registration substance. 56-day NOEC, EC₁₀ and EC₅₀ values of ≥1000, >1000 and >1000 mg/kg dwt respectively, have been determined for the effects on the reproduction of Eisenia fetida, based on nominal concentrations. 28-day NOEC and LC₅₀ values of ≥1000 and >1000 mg/kg dwt have been determined for the survival and growth (as weight) of Eisenia fetida, based on nominal concentrations. These results are equivalent to ≥556, >556 and >556 mg/kg dwt respectively, when normalised to 2% organic carbon content.

An OECD TG 216 soil microorganisms (nitrogen transformation) is available for the registration substance. 28-day EC₅₀, EC₁₀ and NOEC values of >100, >100 and ≥100 mg/kg dry weight have been determined for the effects of the test substance on the nitrogen formation rate of soil microorganisms, based on nominal concentrations. These values are equivalent to >357, >357 and ≥357 mg/kg dry weight when normalised to 2% organic carbon content.

Approach to Chemical Safety Assessment

Acute aquatic toxicity data are available with ViM4Q. The data show no acute effects at or above the limit of solubility of the substance.

ViM4Q is highly adsorptive (log K_ow/K_oc >5) and is likely to be very persistent in soil. ViM4Q is, therefore, assigned to soil Hazard Category 3, in accordance with REACH Guidance Chapter R.7c, because there is indication that the substance is highly adsorptive in soil but there is no evidence of toxicity in aquatic tests.

For Hazard Category 3 substances, the approach for screening assessment is to conduct a PEC x 10/PNECscreen based on the equilibrium partitioning method (EPM) and to conduct a confirmatory long-term soil test with the most sensitive organism group as indicated from aquatic toxicity data.

As there were no effects observed with aquatic organisms, there is an absence of a clear indication of selective toxicity. An earthworm reproduction test under OECD TG 222 has therefore been carried out, in compliance with the guidance. In addition, a soil microorganism toxicity test under OECD TG 216 has also been carried out.

No effects on soil organisms were observed in these tests at the highest concentrations tested (1000 mg/kg dwt and 100 mg/kg dwt, respectively).

It is not possible to derive a robust PNEC for the purposes of a soil screening assessment from acute aquatic toxicity testing because no effects were observed in the aquatic studies and no PNECaquatic has been derived. The screening assessment based on EPM cannot therefore be conducted. However, the requirement to conduct an OECD TG 208 terrestrial plant test in addition to the long-term earthworm test and the soil microorganisms test is waived for the following reasons:

•       The predominant exposure pathway for plants is through uptake via the roots of dissolved test substance present in the pore water. ViM4Q has such low solubility that the majority of the substance will be sorbed to the organic carbon in the soil and only very minimal amounts will be dissolved in the pore water and, thus, available for plant uptake.

•       The substance has a predicted log K_ow of 9.0. It is known that high log K_ow values limit the toxicity of a substance by limiting its bioavailability. This is true for substances acting by non-polar narcosis such as neutral organics.

•       REACH Guidance Chapter R.7c states that for strongly adsorbing or binding substances soil-dwelling organisms that feed on soil particles (e.g. earthworms) are most relevant. In addition, it is stated that for strongly adsorbing or binding substances, preference should be given to test designs and test organisms that cover exposure via ingestion or strong soil particle contact, as this is likely the most relevant exposure route for such substances.

•       Earthworms are the most relevant species for terrestrial exposure. A long-term test with earthworms has been conducted and no effects were observed.

Since the aquatic and terrestrial data available for ViM4Q all show no effects at the highest concentrations tested, in accordance with ECHA guidance, these tests are adequate for terrestrial risk characterisation and no further terrestrial toxicity tests are required. Therefore, the requirement for an OECD TG 208 study with the registration substance is waived.