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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Toxicity to microorganisms: ASRI NOEC 32 mg/l (OECD 209), based on read-across from a structurally-related substance.

Key value for chemical safety assessment

Additional information

No data are available for the submission substance, 2,4,6,8.10-penta methylcyclopentasiloxane.

However, the substance is predicted to hydrolyse rapidly to methylsilanediol, which is then expected to hydrolyse further to methylsilanetriol .

Therefore, good quality data for the structurally-related substance dichloro(methyl)silane (CAS 75-54-7), have been read across.

Dichloro(methyl)silane and methylsilanediol are within an analogue group of substances that exhibit some evidence of toxicity to microorganisms. Dichloro(methyl)silane hydrolyses very rapidly to methylsilanediol ,and then more slowly to methylsilanetriol.

The ultimate hydrolysis product of the registration substance (methylsilanetriol) is not within this analogue group, as it does not have a Si-H bond. Methylsilanetriol is, however, within an analogue group of substances that exhibit no evidence of toxicity to microorganisms. The intermediate hydrolysis product of the registration substance (methylsilanediol) is more relevant to the WWTP exposure than the triol, given the typical residence time in a WWTP (personal communication) and represents a worst-case for toxicity to microoganisms.

It is therefore considered valid to read-across the results for dichloro(methyl)silane, as a worse case, to fill the data gap for the registered substance.

Additional information is given in a supporting report (PFA, 2013k) attached in Section 13 of the IUCLID 5 dossier.

An ASRI EC50 of 160 mg/l and a NOEC of 32 mg/l for toxicity to microorganisms were determinedfor dichloro(methyl)silane. It is likely that the inhibition was influenced by the low pH levels at the higher loading rates, but the pH at the NOEC was 7, and therefore the NOEC is considered the most useful and representative result.

The study is considered to be reliability 1 (reliable without restrictions); the read across of the result is considered to be reliability 2 (reliable with restrictions).