Diphenylsilanediol

Biodegradation in water: screening tests

Description of key information

Biodegradation in water (screening tests): 0% in 28 days (OECD TG 310), read-across from a structurally related substance. 

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

There are no reliable ready biodegradation data available for diphenylsilanediol (CAS 947-42-2), therefore good quality data for the structurally-related substance, trichloro(phenyl)silane (CAS 98-13-5), have been read across. Trichloro(phenyl)silane very rapidly hydrolyses to the silanol hydrolysis product phenylsilanetriol, which is structurally similar to the registration substance diphenylsilanediol. The other hydrolysis product is hydrogen chloride. Hydrogen chloride is inorganic and biodegradation is not relevant.

Trichloro(phenyl)silane (CAS 98-13-5) and diphenylsilanediol (CAS 947-42-2) are within an analogue group of substances within which, in general, there is no evidence of any significant biodegradation (once hydrolysis and subsequent biodegradation of alkoxy/acetoxy groups where present has been taken into account).

This analogue group for the ready biodegradability endpoint consists of a number of sub-classes of substances (based on structure/functionality) with different main codes (used to represent the different sub-classes). However, read-across is carried out between substances with the same main code in most cases.

The table below presents ready biodegradation data for substances within the sub-class of III-22 (chlorosilanes, siloxanes, silanes and alkoxysilanes etc with aryl functionality in side chain after any very rapid hydrolysis has been accounted for).

Trichloro(phenyl)silane (CAS 98-13-5) and diphenylsilanediol (CAS 947-42-2) are members of this sub-class.

It is therefore considered valid to read-across the results for trichloro(phenyl)silane (CAS 98-13-5) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13 of the IUCLID 5 dossier.

Table: Ready biodegradation data available for substances within the relevant sub-class III-22 of chemicals

CAS	Name	Main code	Readily biodegradable? Yes/no	Result: Biodegradation after 28 days (%)	Guideline	Test type	PFA Klimisch code	Result: Biodeg (%)	Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for[1]
052301-18-5	Tris[(1-methylethenyl)oxy]phenylsilane	III-22	Yes	96%	MITI	BOD	1a	96	36
None47	p-(trihydroxysilyl)styrene	III-22	No	26% BOD; 29% TOC; 100% HPLC	OECD 301C	BOD/DOC	1a	29	2
166255-23-8	4,6-Bis(Carbonylphenyl)-2(3(Triethoxysilyl)propyl)-1,3-Phenylenbisphenylmethanon OR ?	III-22	No	5%	OECD 301D	BOD	1a	5	-16
017890-10-7	Benzenamine, N-[(dimethoxymethylsilyl)methyl]-	III-22	yes but not meeting 10-day window	59-63%	OECD 301F	BOD	1a	63	43
250783-08-5	3-[(4'-acetoxy-3'-methoxyphenyl)propyl]trimethoxysilane	III-22	No	30%	OECD 301D	BOD	1a	30	10
None1	3-(3-Chloro-4-fluorophenyl)propyldimethylchlorosilane	III-22C	No	8%	OECD 301B	CO2	1a	8	-10
000098-13-5	Trichloro(phenyl)silane	III-22C	No	0% after 60d	OECD 310 and ISO Guideline 14593	CO2	1a	0	0

[1]The negative values in this column are where the biodegradation rate observed in the test is less than that expected assuming only alkoxy/acetoxy parts biodegrade. This could be due to low solubility of parent substance or low rates of hydrolysis. These values should in effect be considered as zero.

In the study with trichloro(phenyl)silane, 0% biodegradation was observed in 28 days.

Trichloro(phenyl)silane hydrolyses very rapidly to phenylsilanetriol and was used in the test as parent substance on the understanding that it would hydrolyse rapidly to produce the silanol.

The study was conducted according to OECD TG 310 and is considered to be reliable. This is selected as the key study.

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

Reference:

PFA, 2013f, Peter Fisk Associates, Biodegradation Main Analogue Group report, PFA.300.005.007