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Description of key information

In accordance with REACH Annex XI, Section 3, there is no need to further investigate the effects of the silanol hydrolysis product dimethylsilanediol in short- or long-term terrestrial toxicity studies because exposure of terrestrial organisms to dimethylsilanediol is absent or not significant (RCR << 1). No chronic effects were observed in a study testing the long-term toxicity of the silanol hydrolysis product, dimethylsilanediol, on the respiration rate and nitrogen transformation of soil microflora (90-day NOEC ≥ 300 mg/kg soil dw). Furthermore, the hazard assessment based on acute and chronic aquatic toxicity studies showed no hazard (all acute aquatic effect values, i.e. E(L)C50, for fish, daphnia and algae were > 100 mg/L; 21-day NOEC in daphnia ≥ 12.6 mg/L; 72 -h NOErC ≥ 118 mg/L in algae). The substance is well soluble and thus increased toxicity in other long term tests is unlikely.

Therefore the risk is already adequately controlled and further testing is not justifiable.

Additional information

The hydrolysis half-life of the registration substance is < 0.6 h at pH 7 and 25 °C. Therefore, the hazard assessment for the terrestrial compartments is based on the silanol hydrolysis product dimethylsilanediol. The other hydrolysis product, methanol, is known for its absence of environmental toxicity (OECD SIDS, 2004).

 

In accordance with REACH Annex XI, Section 3, there is no need to further investigate the effects of the silanol hydrolysis product dimethylsilanediol in short- or long-term terrestrial toxicity studies because exposure of terrestrial organisms to dimethylsilanediol is absent or not significant (RCR << 1). No chronic effects were observed in a study testing the long-term toxicity of the silanol hydrolysis product, dimethylsilanediol, on the respiration rate and nitrogen transformation of soil microflora (90-day NOEC ≥ 300 mg/kg soil dw). Furthermore, the hazard assessment based on acute and chronic aquatic toxicity studies showed no hazard (all acute aquatic effect values, i.e. E(L)C50, for fish, daphnia and algae were > 100 mg/L; 21-day NOEC in daphnia ≥ 12.6 mg/L; 72-h NOErC ≥ 118 mg/L in algae). The substance is well soluble and thus increased toxicity in other long term tests is unlikely.

Therefore the risk is already adequately controlled and further testing is not justifiable.

In addition, testing for toxicity to terrestrial organisms is not considered necessary because:

- The substance is used under highly controlled conditions and therefore, exposure of the terrestrial compartment is low.

- The silanol hydrolysis product is not readily biodegradable but has a low potential for bioaccumulation (log Kow < 3.0) and there is no reason to expect any specific meachanism of toxicity beyond narcosis.

- A data set for acute and chronic toxicity to aquatic species, and a long-term toxicity study on soil microflora, are available for the silanol hydrolysis product. No effects were observed up to the highest concentrations tested in the acute and chronic aquatic studies, and chronic soil microflora study. The occurrence of more severe toxic effects in the terrestrial compartment that were not expressed in these studies are considered unlikely.  

- A PNEC soil was calculated by the equilibrium partitioning method and has been derived for the purpose of the chemical safety assessment. The risk characterisation ratios are below 1.

Overall, it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further testing is not considered necessary. Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6 and Chapters 7, 9 and 10 of the Chemical Safety Report.

References:

OECD SIDS, 2004: SIDS Initial Assessment Report for Methanol, SIAM 19, Berlin, Germany, 19-22 October 2004, Methanol, CAS 67-56-1