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Environmental fate & pathways

Biodegradation in soil

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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 the abiotic degradation study (IUCLID 5.1.2), and the environmental hazard assessment is based on those.
No.:
#1
No.:
#2

Description of key 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.

Key value for chemical safety assessment

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 registered substance is ‘not readily biodegradable’ based on read-across from a structural analogue. The registration substance hydrolyses (DT50 = 0.4 h) to phenylsilanetriol and methanol. 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 non-silanol hydrolysis product, methanol, is readily biodegradable. 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 those identified as the hydrolysis products in Section 5.1.2 of the IUCLID.

 

The silanol hydrolysis product of the registered substance is considered to be not B based on its low log Kow of -0.021. Therefore, further testing for persistence 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.

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