Isobutyldimethoxymethylsilane

Biodegradation in water: screening tests

Description of key information

Biodegradation in water (screening tests):36% in 28 days (9.97 mg/l) and 47% in 28 days (20.1 mg/l) % in 28 days (OECD 301B), read-across from a structurally related substance. No significant biodegradation of the silanol hydrolysis product is expected.

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 isobutyl(dimethoxy)methylsilane (CAS 18293-82-8), therefore good quality data for the structurally-related substance, isobutyl(trimethoxy)silane (CAS 18395-30-7), have been read across. Both substances hydrolyse rapidly, and extensive or complete hydrolysis in the course of the 28-day ready biodegradation study is to be expected. Both have structurally similar silanol hydrolysis products, isobutyl(methyl)silanediol and (2-methylpropyl)silanetriol, respectively. The other hydrolysis product of both substances is methanol. Methanol is readily biodegradable (OECD 2004). Isobutyl(dimethoxy)methylsilane (CAS 18293-82-8) and isobutyl(trimethoxy)silane (CAS 18395-30-7) 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 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 I-2 of Alkoxysilanes, silanols, acetoxysilanes and chlorosilanes with Si part of low-biological reactivity, once any hydrolysis is accounted for. Isobutyl(dimethoxy)methylsilane (CAS 18293-82-8) and isobutyl(trimethoxy)silane (CAS 18395-30-7) are members of this sub-class. It is therefore considered valid to read-across the results for isobutyl(trimethoxy)silane (CAS 18395-30-7) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013f) attached in Section 13.

Table: Ready biodegradation data 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	Test type	Klimisch code	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	CO2	1	0
013154-25-1	Chlorotri(3-methyl-propyl)silane	I-2-M-C	No	0%	OECD 301B	CO2	1	0
139147-73-2	Silane, dichlorodicyclopentyl-	I-2-D-C	No	0.80%	OECD 301D	BOD	2	1
000098-12-4	Cyclohexyltrichlorosilane	I-2-D-C	No	0%	OECD 301C	BOD	1	0
000124-70-9	Dichloro(methyl)(vinyl)silane	I-2-D-C	No	-6.78% (0%)	OECD 301 A	DOC	1	0
017865-32-6	Cyclohexyldimethoxymethylsilane	I-2-D-Me-H	No	15-17%	OECD 301D	BOD	1	-5
126990-35-0	Dicyclopentyldimethoxysilane	I-2-D-Me-M	No	12%	OECD 301C	BOD	1	-5
None46	t-butoxycyclopentyldimethoxysilane	I-2-D-Me-M	No	15% BOD; 25% TOC; 100% GC	OECD 301C	BOD/DOC	1	7
017689-77-9	Triacetoxyethylsilane	I-2-T-A	Yes	74% in 21 days	EC C4-A	DOC	1	-1
017980-47-1	Triethoxyisobutylsilane	I-2-T-Et-M	Yes	75%	OECD 301D	BOD	1	15
002943-75-1	Triethoxyoctylsilane	I-2-T-Et-M	No	31.50%	OECD 301D	BOD	1	-11
035435-21-3	Triethoxy(2,4,4-trimethylpentyl)silane	I-2-T-Et-M	No	13%	OECD310	CO2	1	-30
016415-13-7	Triethoxyhexadecylsilane	I-2-T-Et-S	No	43% by BOD; 74% by HPLC	MITI	BOD	1	16
001067-25-0	Trimethoxypropylsilane	I-2-T-Me-H	No	54%	Annex V C4-A	DOC	1	4
087135-01-1	1,6-Bis(trimethoxysilyl)hexane	I-2-T-Me-H	yes but not meeting 10-day window	74%	OECD 301B	CO2	1	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 microorganismsand the like"[2]	BOD/DOC	1	18
018395-30-7	Isobutyl(trimethoxy)silane	I-2-T-Me-H	No	36 - 47%	OECD 301B	CO2	1	4
002768-02-7	Trimethoxyvinylsilane	I-2-T-Me-H	No	51%	OECD 301F	BOD	1	-9
142877-45-0	Silane, trimethoxy(1,1,2-trimethylpropyl)-	I-2-T-Me-S	No	31%	OECD 301D	BOD	1	-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 isobutyl(trimethoxy)silane (CAS 18395-30-7), the substance attained 36% and 47% biodegradation in 28 days at 9.97 mg/l and 20.1 mg/l, respectively.

Isobutyl(trimethoxy)silane (CAS 18395-30-7) hydrolyses within the timescale of the ready biodegradation study to(2 -methylpropyl)silanetrioland methanol.The biodegradation observed in the study is attributable to the biodegradation of the methanol hydrolysis product. Methanol is readily biodegradable (OECD, 2004). No significant biodegradation is expected for the silanol hydrolysis product.

The study was conducted according to OECD 301B and is considered to be 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).

References:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1.

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