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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Short-term toxicity to algae: 72 hour ErC50 >118 mg/l and NOEC 118 mg/l (highest concentration tested) (OECD 201), read-across from the silanol hydrolysis product of the registration substance, dimethylsilanediol (CAS 1066-42-8).

Key value for chemical safety assessment

EC50/LC50 for freshwater algae:
118 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 algal inhibition data available for 2,2,4,4,6,6-hexamethylcyclotrisilazane (CAS 1009-93-4), therefore good quality data for its silanol hydrolysis product, dimethylsilanediol (CAS 1066-42-8) have been read across. The other hydrolysis product of the registration substance is ammonia/ammonium ions.

A 72 hour ErC50 value of >118 mg/l and NOEC of 118 mg/l (highest concentration tested) have been determined for the effects of dimethylsilanediol (CAS 1066-42-8) on growth rate and biomass of Pseudokirchneriella subcapitata.

Refer to the discussion in the Section 6 endpoint summary for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.

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 five day EC50 of 2.0 mg NH3/L, and a 14 day LOEC of 3.0 mg NH3/L has been reported for toxicity of ammonia to algae.