Trimethoxy(2,4,4-trimethylpentyl)silane

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Data waiving:

other justification

Justification for data waiving:

other:

Transformation products:

yes

Remarks:

Degradation is principally expected via abiotic transformation (aqueous). The transformation products expected are those identified in IUCLID section 1.10 "transformation of the registered substance", the environmental hazard assessment is based on those.

No.:

#1

No.:

#2

Description of key information

The simulation test in soil as well as the identification of degradation products do not need to be conducted as:

- in accordance with Column 2 of REACH Annex IX, the chemical safety assessment according to Annex I indicates that this is not necessary,

and

- in accordance with Section 3 of REACH Annex XI, exposure of the aquatic/sediment compartment is not significant.

Additional information

The soil simulation test and identification of degradation products do not need to be conducted as:

- in accordance with Column 2 of REACH Annex IX, the chemical safety assessment according to Annex I indicates that this is not necessary, and

- in accordance with Section 3 of REACH Annex XI, exposure of the soil compartment is not significant. 

Many organosilicon compounds hydrolyse rapidly to a silanol and a by-product such as ethanol, methanol or HCl. For most organosilicon compounds, little or no degradation is observed in ready biodegradation studies once degradation of any readily biodegradable hydrolysis by-product is accounted for. This is supported by a small number of simulation studies that show limited biodegradation. Therefore, most organosilicon compounds either meet the criteria for persistence or produce transformation products that may meet the criteria for persistence based on currently available data. The available evidence regarding biodegradation and persistence of organosilicon compounds is summarised in an attached document in Section 13 (PFA 2021).

The registered substance is ‘not readily biodegradable’ based on read-across from a structural analogue. The registered substance hydrolyses rapidly in the environment (DT50 = 5.7 h at pH 7 and 20-25 °C, QSAR), forming (2,4,4-trimethylpentyl)silanetriol and methanol (CAS No. 67-56-1). Thus, the environmental fate assessment is based on the hydrolysis products (2,4,4-trimethylpentyl)silanetriol and methanol rather than the parent substance. The exposure assessment and risk characterisation is carried out for the silanol hydrolysis product of the substance on the basis that it is not biodegradable. Risk characterisation ratios are below 1. The alcohol hydrolysis product, methanol, is readily biodegradable and has a low log Pow of -0.82 to -0.64 (OECD SIDS, 2004), and thus is negligible for the assessment. Therefore, further testing for biodegradation would not affect the outcome of the environmental risk characterisation.

Since degradation of the registration substance is expected to be principally via abiotic transformation under the aqueous conditions of a degradation simulation study, the transformation products expected in the environment are (2,4,4-trimethylpentyl)silanetriol and methanol. The silanol hydrolysis product of the registered substance is considered to be not B based on its low log Pow of 0.9 (QSAR), which demonstrates a low potential for adsorption to sediment and soil. Therefore, further testing for persistence is not necessary and would not affect the overall outcome of the PBT/vPvB assessment.

The chemical safety assessment does not indicate any need to investigate further the degradation of the substance, or either of its hydrolysis products, at the present time. 

References:

OECD SIDS, 2004a. Ethanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.

OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications. 

PFA (2021): Background to persistence assessment of organosilicon compounds, PFA.923.001.001, February 2021