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Trichloro(4-methylphenyl)silane (CAS 701-35-9) hydrolyses rapidly (<1 min at pH 4-9 and 1.5 °C) in water and humid environments to the corresponding hydrolysis products (4-methylphenyl)silanetriol and hydrochloric acid. The ECHA guidance R.16 states that “for substances where hydrolytic DT50 is less than 12 h, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself” (ECHA, 2016). TGD (EC, 2003) and ECHA guidance R.16 (ECHA, 2016) also suggest that when the hydrolysis half-life is less than 12 h, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity testing.

Experimental data on the toxicity of trichloro(4-methylphenyl)silane (CAS 701-35-9) to aquatic organisms are not available. Thus the toxicity of the substance to aquatic invertebrates and algae was assessed using read across data from the structurally similar substance trichloro(phenyl)silane (CAS 98-13-5). The substances share very similar silanol hydrolysis products (i.e. (4-methylphenyl)silanetriol and phenylsilanetriol, respectively). The other hydrolysis product is in both cases hydrochloric acid. Both substances will hydrolyse within the timescale of an aquatic toxicity test. Further information on the read across approach can be found in the attached justification in the respective target entry and in the overall justification for grouping of substances attached in IUCLID Section 13.

The available aquatic studies with the analogue substance were all conducted according to the appropriate OECD guidelines and GLP standards. The results showed no adverse effects to aquatic organisms. The short term toxicity study (OECD 202) with Daphnia magna resulted in an EC50 (48 h) of > 100 mg/L (nominal) and no influence of the analogue substance on the growth rate of the freshwater algae species Pseudokirchneriella subcapitata (OECD guideline 201) was recorded (ErC50 (72 h) > 100 mg/L and NOErC (72 h) ≥ 100 mg/L).

On this basis, no adverse effects are anticipated by the target substance to aquatic organisms.


EC (2003). European Union Technical Guidance Document on Risk Assessment for New and Existing Substances, Part II, European Chemicals Bureau, 2003.

ECHA (2016). REACH Guidance on Information Requirements and Chemical Safety Assessment Chapter R16: Environmental Exposure Estimation Version: 3.0 February 2016.

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