Dichloro(dimethyl)silane

Biodegradation in water: screening tests

Description of key information

Biodegradation in water (screening tests): 0% in 28 days (OECD 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 ready biodegradation data available for dichloro(dimethyl)silane, therefore good quality data for the structurally-related substance, trimethylsilanol (CAS 1066-40-6), have been read across. The silanol hydrolysis product of dichloro(dimethyl)silane is structurally similar to trimethylsilanol. The other hydrolysis product of dichloro(dimethyl)silane is hydrogen chloride. Hydrogen chloride is inorganic and biodegradation is not relevant.

Dichloro(dimethyl)silane and trimethylsilanol 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 has been taken into account.

This analogue group for the ready biodegradability endpoint consists of a number of sub-classes (based on structure/functionality) of substances 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 I-2 of Alkoxysilanes, silanols, acetoxysilanes and chlorosilanes, etc, where the Si part is of low-biological reactivity, once any hydrolysis is accounted for.Dichloro(dimethyl)silane (CAS 75 -78 -5) and trimethylsilanol (CAS 1066 -40 -6) are members of this sub-class.

It is therefore considered valid to read-across the results for trimethylsilanol 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.

Ready biodegradation data available for substances within the relevant sub-class I-2 of chemicals

CAS	Name	Main code	Readily biodegradable? Yes/no	Result: Biodegradation after 28 days (%)	Guideline	Reliability	Corrected % biodegradation once alkoxy/acetoxy biodegradation is accounted for[1]
001066-40-6	Hydroxytrimethylsilane	I-2	No	0%	OECD 310 and ISO Guideline N 14593	1a	0
013154-25-1	Chlorotri(3-methyl-propyl)silane	I-2-M-C	No	0%	OECD 301B	1a	0
139147-73-2	Silane, dichlorodicyclopentyl-	I-2-D-C	No	0.80%	OECD 301D	2b	1
000098-12-4	Cyclohexyltrichlorosilane	I-2-D-C	No	0%	OECD 301C	1a	0
000124-70-9	Dichloro(methyl)(vinyl)silane	I-2-D-C	No	-6.78%	OECD 301 A	1a	0
017865-32-6	Cyclohexyldimethoxymethylsilane	I-2-D-Me-H	No	15-17%	OECD 301D	1a	-5
126990-35-0	Dicyclopentyldimethoxysilane	I-2-D-Me-M	No	12%	OECD 301C	1	-5
None46	t-butoxycyclopentyldimethoxysilane	I-2-D-Me-M	No	15% BOD; 25% TOC; 100% GC	OECD 301C	1a	7
017689-77-9	Triacetoxyethylsilane	I-2-T-A	Yes	74% in 21 days	EC C4-A	1a	-1
017980-47-1	Triethoxyisobutylsilane	I-2-T-Et-H	Yes	75%	OECD 301D	1a	15
002943-75-1	Triethoxyoctylsilane	I-2-T-Et-M	No	31.50%	OECD 301D	1a	-11
035435-21-3	Triethoxy(2,4,4-trimethylpentyl)silane	I-2-T-Et-M	No	13%	OECD310	1a	-30
016415-13-7	Triethoxyhexadecylsilane	I-2-T-Et-S	No	43% by BOD; 74% by HPLC	MITI	1c	16
001067-25-0	Trimethoxypropylsilane	I-2-T-Me-H	No	54%	Annex V C4-A	1a	4
087135-01-1	1,6-Bis(trimethoxysilyl)hexane	I-2-T-Me-H	yes but not meeting 10-day window	74%	OECD 301B	1a	24
None45	Mixture of 1,1- and 1,2-bis(trimethoxysilyl)ethane	I-2-T-Me-H	Yes	93% BOD; 78% TOC; 100% GC (ethanol?)	"Biodegradation study of chemical substances by microorganisms and the like"[2]	1a	18
018395-30-7	Trimethoxy(2-methylpropyl)silane	I-2-T-Me-H	No	36 - 47%	OECD 301B	1a	4
002768-02-7	Trimethoxyvinylsilane	I-2-T-Me-H	No	51%	OECD 301F	1a	-9
142877-45-0	Silane, trimethoxy(1,1,2-trimethylpropyl)-	I-2-T-Me-S	No	31%	OECD 301D	1a	-2

[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.

 

[2]Stipulated in "Testing Method for New Chemical Substances etc." (Kanhogyo No.5, Yakuhatsu 615, 49Kikyoku No.392, July 13, 1974 )

In the study with trimethylsilanol (CAS 1066 -40 -6), 0% biodegradation was observed in 28 days.

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

The study is considered to be reliability 1 (reliable without restrictions); the 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