Reaction mass of 1,1,1,5,5,5-hexamethyl-3-phenyl-3-((trimethylsilyl)oxy)trisiloxane and 1,1,1,7,7,7-hexamethyl-3,5-diphenyl-3,5-bis[(trimethylsilyl)oxy]tetrasiloxane and 1,1,1,9,9,9-hexamethyl-3,5,7-triphenyl-3,5,7-tris((trimethylsilyl)oxy)pentasiloxane

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 EC₂₅ and EC₅₀ values of >100 mg/kg dwt were reported for the effects on the nitrate formation rate of soil microorganisms, based on nominal concentrations. Nitrate formation rates were significantly reduced in all treatment groups compared to the control, which gives a 28-day LOEC of 1.2 mg/kg dwt. However, a dose response relationship was not observed, suggesting the effects to be due to a non-toxic mechanism. The EC₂₅, EC₅₀ and LOEC values are equivalent to >400, >400 and 4.8 mg/kg dwt when normalised to 2% organic carbon.

Approach to Chemical Safety Assessment

The terrestrial testing strategy and chemical safety assessment for phenyl silsesquioxanes (EC No. 939-487-8) is based on a Weight-of-Evidence (WoE) approach.

 

REACH Guidance Chapter R.7c, Section R.7.11.5.3, states that ‘it will normally not be possible to derive a robust PNEC for the purposes of a soil screening assessment from acute aquatic toxicity testing showing no effect. This is particularly true for poorly soluble substances. Where the water solubility is <1 mg/l, the absence of acute toxicity can be discounted as reliable indicator for potential effects on soil organisms due to the low exposures in the test. The absence of chronic or long-term effects in aquatic organisms up to the substance solubility limit, or of acute effects within the solubility range above 10 mg/l can be used as part of a Weight-of-Evidence argument to modify/waive the data requirements of Annex IX and X’.

 

REACH Guidance Chapter R.7c, Section R.7.11.5.3, further states that ‘where there is no toxicity L(E)C₅₀ in the standard acute aquatic toxicity tests at >10 mg/l, or no effects in chronic toxicity at the limit of water solubility, or the screening assessment based on EPM shows no concern, then a single short-term soil test on a suitable species would be adequate to meet the requirements of Annex IX. The soil PNEC would be derived by application of appropriate assessment factors to the aquatic data and the soil short-term data, and the lowest value taken. Where the substance is highly adsorptive, e.g. where the log K_ow/K_oc >5, and/or the substance is very persistent in soil, this single test should be a long-term test. Substances with a half-life >180 days are considered to be very persistent in soil. This persistence would be assumed in the absence of specific soil data, unless the substance is readily degradable. The choice of test (invertebrate / plant / micro-organism) would be based on all the information available, but in the absence of a clear indication of selective toxicity, an invertebrate (earthworm or collembolan) test is preferred.’

 

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

 

Phenyl silsesquioxanes is highly adsorptive (log K_ow/K_oc >5) and is likely to be very persistent in soil, therefore a long-term soil test has been conducted. 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).

Since the aquatic and terrestrial data available for phenyl silsesquioxanes 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.