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Short-term toxicity to aquatic invertebrates

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Description of key information

A measured 48 hour EC50 value of >117 mg/l, and NOEC of 117 mg/l (highest concentration tested in both cases), have been determined for the effects of dimethylsilanediol (CAS 1066-42-8) on mobility of Daphnia magna. The results are read across for the purpose of chemical safety assessment of 2,2,4,4,6,6-hexamethylcyclotrisilazane (CAS 1009-93-4), which in view of the very rapid hydrolysis, focuses on its hydrolysis products, dimethylsilanediol and ammonia/ammonium ions.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
117 mg/L

Additional information

2,2,4,4,6,6-Hexamethylcyclotrisilazane hydrolyses very rapidly in water to give dimethylsilanediol and ammonia/ammonium ions. There are no reliable short-term invertebrate toxicity data available for 2,2,4,4,6,6-hexamethylcyclotrisilazane (CAS 1009-93-4), therefore good quality data for dimethylsilanediol (CAS 1066-42-8) have been read across. Dimethylsilanediol (CAS 1066-42-8) is not susceptible to further hydrolysis under the conditions of the study. The other hydrolysis product is ammonia/ammonium ions.

Reliable short-term test results are available for ammonia sourced from the Environment Agency Proposed EQS for Water Framework Directive Annex VIII Substances: Ammonia (un-ionized) 2007. A 96 h LC50 of 0.16 mg unionised mg NH3/L has been reported for short-term toxicity of ammonia to aquatic invertebrates.