1,1,1,3,3,3-hexamethyldisilazane

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1991-12-09 to 1991-12-10

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

The study was conducted according to an appropriate standard method and in compliance with GLP but full details are not available

Qualifier:

according to guideline

Guideline:

ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Direct addition

Concentration inoculum 6 g/l TS

Test organisms (species):

activated sludge

Details on inoculum:

- Source: Laboratory treatment plant (taken 06/12/1991)

- Pretreatment: None

Limit test:

no

Remarks on exposure duration:

Not specified Guideline says 30 min to 3hr

Nominal and measured concentrations:

1000, 1800, 3200, 5600, 10000 mg/l

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

6 670 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: test duration not specified. However, it was conducted in accordance with OECD 209, which requires a time of 30 minutes to 3 hours

Results with reference substance (positive control):

The validity of the study guide was reviewed using a graphical analysis of the reference substance.

Test substance concentration (mg/l)	Respiration rate (mg O2/l/h)	% Inhibition respiration rate
1000	39.0	0.0
1800	39.0	0.0
3200	34.0	5.6
5600	21.0	41.7
10000	8.6	76.1

 

Conclusions:

An EC50 value of 6670 mg/l (nominal) for toxicity to microorganisms (respiration rate) was determined in a reliable study conducted according to an appropriate standard method and in compliance with GLP but full details are not available.

Description of key information

EC₅₀ 6670 mg/l (nominal) (respiration rate) (ISO 8192), silanol hydrolysis product, trimethylsilanol (CAS 1066-40-6).

Key value for chemical safety assessment

EC50 for microorganisms:

6 670 mg/L

Additional information

There are no reliable microorganism toxicity data available for hexamethyldisilazane (CAS 999-97-3). Therefore good quality data for the silanol hydrolysis product, trimethylsilanol (CAS 1066-40-6), have been presented.

Trimethylsilanol is within an analogue group of substances within which, in general, there is no evidence of significant toxicity to microorganisms.

The table below presents microorganism toxicity data available for substances containing alkoxysilanes (methoxy and ethoxy), silanols, acetoxysilanes and chlorosilanes. Trimethylsilanol (hydroxytrimethylsilane) is a member of this group.

Hexamethyldisilazane itself is in a different analogue group (nitrogen attached to Si) but it is not appropriate to consider data for this analogue group as the data available are for substances with non-Si hydrolysis products that are amino alkyl substances, which is not the case for hexamethyldisilazane.

Additional information is given in a supporting report (PFA, 2013j) attached in Section 13.

Table: Microorganism toxicity data relevant to the submission substance

CAS	Name	Main code	Guideline Number	Test method	Species	Reliability	Duration	Result: E(I)C50 (mg/l)	Result: NOEC (or EC10/ EC20) (mg/l)
1066-40-6	Hydroxytrimethylsilane	I-2	OECD 209 and ISO 1892	ASRI		2	Uncertain	6670
31795-24-1	Potassium methylsilanetriolate	I-2	OECD 209	ASRI		1	3 h		EC10 >100 mg/l
139147-73-2	Silane, dichlorodicyclopentyl-	I-2-D-C	OECD 209	ASRI		1	3 hr	>100
124-70-9	Dichloro(methyl)(vinyl)silane	I-2-D-C	OECD 209	ASRI		1	3hr	>100 mg/l
126990-35-0	Dicyclopentyldimethoxysilane	I-2-D-Me-M	OECD 209/EU C11/Huls AG method (WOE)	ASRI/ASRI/oxygen consumption P. putida (WOE)		1/1/2 (WOE)	3hr; 3hr; 3hr (WOE)	>water solubility; >water solubility; >water solubility (WOE)
1000-50-6	Butylchlorodimethylsilane	I-2-M-C	88/302/EC	ASRI		1	3h	>340
13154-25-1	Chlorotri(3-methyl-propyl)silane	I-2-M-C	OECD 209	ASRI		2	3 hr	>1000 (nominal, parent)	100 (nominal, parent)
5894-60-0	Trichloro(hexadecyl)silane	I-2-T-C	OECD 209	ASRI		1	3h	>1000	≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate
75-94-5	Trichloro(vinyl)silane	I-2-T-C	OECD 209	ASRI		1	3hr	>100 mg/l
1185-55-3	Trimethoxy(methyl)silane	I-2-T-Et-H	OECD 209	ASRI		1	3hr	>100 mg/l	EC10 >100 mg/l
17980-47-1	Triethoxyisobutylsilane	I-2-T-Et-M	OECD 209	ASRI		1	3h	>1000mg/l	≥1000 mg/l
2943-75-1	Triethoxyoctylsilane	I-2-T-Et-M	OECD 209	ASRI		1	3 hr	>1000	≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate
16068-37-4	4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane	I-2-T-Et-M	DIN 38 412, Part 8 (Pseudomonas cell multiplication inhibition test)	growth inhibition test	P. putida	1	16 h	>8000 mg/l	8000 mg/l
35435-21-3	Triethoxy(2,4,4-trimethylpentyl)silane	I-2-T-Et-M	OECD 209	ASRI		1	3hr	>100 mg/l
87135-01-1	1,6-Bis(trimethoxysilyl)hexane	I-2-T-Me-H	OECD 209	ASRI		1	3h	>1000 mg/l
16415-12-6	Hexadecyltrimethoxysilane	I-2-T-Me-H	OECD 209	ASRI		1	3 hr	>1000	Nitrification control indicated no heterotrophic inhibition of respiration rate.
142877-45-0	Silane, trimethoxy(1,1,2-trimethylpropyl)-	I-2-T-Me-S	OECD 209	ASRI		1	3 hr	>1000	≥1000 mg/l

In the study with trimethylsilanol,an EC₅₀ value of 6670 mg/l (nominal) for toxicity to microorganisms (respiration rate) was determined in a reliable study conducted according to an appropriate standard method and in compliance with GLP but full details are not available.

The other hydrolysis product of 1,1,1,3,3,3-hexamethyldisilazane is ammonia. Typical levels of free ammonia in municipal sewage treatment plants range from ca. 12-50 mg/l in the sewage treatment plant collection system (Lehr, Jay; Keeley, Jack; Lehr, Janet Water Encyclopedia, Volumes 1-5. (section 1.4.49). John Wiley & Sons.). For the registration substance, the predicted environmental concentrations of the hydrolysis product ammonia in a sewage treatment plant are negligible compared to this typical level (CSR Section 9). No PNECstp is derived for ammonia: this is discussed further in CSR Section 10.

An IC₅₀ value of 1700 mg/l was reported in secondary literature (Union Carbide) for the registered substance. However, the original reference was not available for review and the reliability of this result is not assignable.