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Classification & Labelling & PBT assessment

PBT assessment

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Administrative data

PBT assessment: overall result

PBT status:
the substance is not PBT / vPvB

The PBT Assessment is based on the criteria set out in the “Guidance on information requirements and chemical safety assessment, Chapter R.11: PBT Assessment” (ECHA, 2017).



Persistence Assessment

The registered substance triethoxy(methyl)silane (CAS No. 2031-67-6) is expected to hydrolyse rapidly (DT50 = 5.5 h) in contact with water to methylsilanetriol (CAS No. 2445-53-6) and ethanol (CAS No. 64-17-5).

A reliable ready biodegradation study is available for the structurally-analogous substance triacetoxyethylsilane (CAS No. 17689 -77 -9), which hydrolyses into the structurally related silanol hydrolysis product ethylsilanetriol and to the non-silanol hydrolysis product acetic acid.

A biodegradation rate of 74% in 21 d (DOC removal) was determined in a reliable study conducted according to the standard test guideline (EU C.4-A) and in compliance with GLP. However, once the biodegradation of the alkoxy/acetoxy groups are accounted for, the corrected % biodegradation resulted in -1%.  Thus, there is no evidence of any significant biodegradation of the silanol hydrolysis product.


In conclusion, the non-silanol hydrolysis products ethanol and acetic acid are readily biodegradable and therefore not persistent. The silanol hydrolysis products ethylsilanetriol and methylsilanetriol are not expected to biodegrade to any significant extent.  Thus, the silanol hydrolysis product of the registered substance meets the screening criteria for persistence and the substance is concluded to be “vP (and P)”.



Bioaccumulation Assessment

Triethoxy(methyl)silane is expected to hydrolyse rapidly in contact with water to methylsilanetriol and ethanol (half-life approximately 5.5 hours at 20-25°C and pH 7). Therefore, the parent substance will not bioaccumulate. The hydrolysis products methylsilanetriol and ethanol have low log Kow values (<3) and, therefore, are not likely to bioaccumulate either. Therefore, the substance does not meet the criteria for bioaccumulation; it is not B and not vB.


Toxicity Assessment

The substance is not considered as T for the environment, since the lowest measured EC50for the substance was >500 mg/l and the lowest predicted EC50for the hydrolysis product was 2115 mg/l. Both do not meet the screening criteria for T for the environment (EC/LC50 <0.1 mg/l). The substance is not classified for specific target organ toxicity, carcinogenicity, mutagenicity or reproductive and developmental toxicity in mammals. The criteria for “T” based on mammalian effects are therefore not met.


Summary and overall Conclusions on PBT or vPvB Properties

The substance is expected to hydrolyse very rapidly in the presence of water into a silanol and alcohol hydrolysis product. The alcohol hydrolysis product is readily biodegradable but the silanol hydrolysis product is not expected to biodegrade to a significant extent and may persist in the environment. However, the silanol hydrolysis product does not meet the criteria for B and T. Therefore, the registered substance is concluded to be “not PBT/vPvB”.