Dichloro(diphenyl)silane

Endpoint summary

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 diphenylsilanediol in short- or long-term terrestrial toxicity studies because exposure of terrestrial organisms to diphenylsilanediol is absent or not significant (RCR << 1). Furthermore, the hazard assessment based on acute aquatic toxicity studies showed only a moderate hazard (lowest acute aquatic effect value, the ErC50 for algae was 9.0 mg/L). The substance is well soluble and thus increased toxicity in 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 approximately 10 sec at pH 7 and 1.5 °C. Therefore, the hazard assessment for the terrestrial compartments is based on the silanol hydrolysis product diphenylsilanediol. The other hydrolysis product, hydrochloric acid,readily dissociates in water into hydrated protons and chloride anions. Thus, it is ionised and neutralisation depends on the buffer capacity of the receiving water. Toxicity only occurs when the buffering capacity of the receiving water is exceeded and pH values fall below pH 6. The pH in rivers and lakes fluctuates within a natural range. The natural pH range in aquatic systems is generally not expected to be perturbed to a relevant extent by anthropogenic emissions when appropriate risk control measures are in place. Variations in effect values of experimental studies can largely be explained by variations in the buffer capacity of the test media (OECD, 2002).

 

In accordance with REACH Annex XI, Section 3, there is no need to further investigate the effects of the silanol hydrolysis product diphenylsilanediol in short- or long-term terrestrial toxicity studies because exposure of terrestrial organisms to diphenylsilanediol is absent or not significant (RCR << 1). Furthermore, the hazard assessment based on acute aquatic toxicity studies showed a moderate hazard (lowest acute aquatic effect value, the ErC50 for algae was 9.0 mg/L). The substance is well soluble and thus increased toxicity in 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 and 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 short-term toxicity to aquatic species is available for the silanol hydrolysis product. Low effects were observed for the short-term fish or aquatic invertebrate studies up to arithmetic mean measured concentrations of 39 and 24 mg/L, respectively. Lower effects were seen in the toxicity study with algae (ErC50 (72 h) = 9 mg/L) and the result from this test was used to derive aquatic PNECs. The occurrence of more severe toxic effects in the terrestrial compartment that were not expressed in the aquatic studies are considered unlikely.  

- Aquatic PNECs were calculated by use of the lowest LC/EC50 in the short-term aquatic toxicity studies (ErC50 = 9 mg/L (algae)) and the appropriate assessment factor 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.