Potassium methylsilanetriolate

Biodegradation in water: screening tests

Description of key information

Biodegradation in water, screening tests: 0% in 28 days (read-across from an analogous/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 potassium methylsilanetriolate (CAS 31795-24-1), therefore good quality data for the structurally-related substance, trimethylsilanol (CAS 1066-40-6), have been read across. Potassium methylsilanetriolate and trimethylsilanol are within an analogue group of substances which,in general,exhibit no evidence of any significant biodegradation of silanol hydrolysis products of the organosilicon substances in the group. 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. Trimethylsilanol attained 0% biodegradation in 28 days.

Potassium methylsilanetriolate dissociates completely into potassium and methylsilanetriolate ions in aqueous solution. The substance as sold is only stable at high pH (pH >12). When the pH is reduced, the concentration of the non-ionised form (methylsilanetriol) increases. The first pKa of methylsilanetriol is approximately 10. At pH 9.0 and below, the substance is no longer in the ionised form and methylsilanetriol predominates. Methylsilanetriol undergoes reversible condensation reactions in solution to give siloxane dimers, linear and cyclic oligomers. The overall rate and extent of condensation is dependent on the amount of substance present (the nominal loading), temperature, pH of the system and what else is present in the solution. Under conditions relevant for the environment (close to neutral pH and low concentration), the neutral monomer (methylsilanetriol) predominates (>99%). The dimers and oligomers are expected to be less biodegradable than the monomer. Therefore, read-across from trimethylsilanol, which is a close structural analogue of methylsilanetriol, is considered to be appropriate.

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 etc. Potassium methylsilanetriolate (CAS 31795-24-1) and trimethylsilanol (CAS 1066-40-6) are members of this sub-class.

It is therefore considered valid to read-across the results for trimethylsilanol (CAS 1066-40-6) 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 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]
1066-40-6	Hydroxytrimethylsilane	I-2	No	0%	OECD 310 and ISO Guideline N 14593	1a	0
13154-25-1	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
98-12-4	Cyclohexyltrichlorosilane	I-2-D-C	No	0%	OECD 301C	1a	0
124-70-9	Dichloro(methyl)(vinyl)silane	I-2-D-C	No	-6.78%	OECD 301 A	1a	0
17865-32-6	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
17689-77-9	Triacetoxyethylsilane	I-2-T-A	Yes	74% in 21 days	EC C4-A	1a	-1
17980-47-1	Triethoxyisobutylsilane	I-2-T-Et-H	Yes	75%	OECD 301D	1a	15
2943-75-1	Triethoxyoctylsilane	I-2-T-Et-M	No	31.50%	OECD 301D	1a	-11
35435-21-3	Triethoxy(2,4,4-trimethylpentyl)silane	I-2-T-Et-M	No	13%	OECD310	1a	-30
16415-13-7	Triethoxyhexadecylsilane	I-2-T-Et-S	No	43% by BOD; 74% by HPLC	MITI	1c	16
1067-25-0	Trimethoxypropylsilane	I-2-T-Me-H	No	54%	Annex V C4-A	1a	4
87135-01-1	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 bymicroorganisms and the like"[2]	1a	18
18395-30-7	Trimethoxy(2-methylpropyl)silane	I-2-T-Me-H	No	36 - 47%	OECD 301B	1a	4
2768-02-7	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 ISO Guideline N 14593 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).