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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Toxicity to microorganisms: EC50 6670 mg/l (nominal) (respiration rate) read-across from the silanol hydrolysis product trimethylsilanol

Key value for chemical safety assessment

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 read across.

Trimethylsilanol is within an analogue group of substances within which, in general, there is no evidence of significant toxicity to microorganisms. Hexamethyldisilazane itself is in a different analogue group (nitrogen attached to Si (main code II-3 -1)), 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.

The table below presents microorganism toxicity data available for substances within the sub-class (based on structure/functionality) with main-code (used to represent the different sub-classes) I-2 of alkoxysilanes (methoxy and ethoxy), silanols, acetoxysilanes and chlorosilanes. Trimethylsilanol (hydroxytrimethylsilane) is a member of this sub-class.

Additional information is given in a supporting report (PFA, 2013j) attached in Section 13 of the IUCLID 5 dossier.

Microorganism toxicity data available for substances within the relevant sub-class I-2 of chemicals

CAS

Name

Main code

Guideline Number

Test method

Species

Reliability

Duration

Result: E(I)C50 (mg/l)

Result: NOEC (or EC10/ EC20) (mg/l)

001066-40-6

Hydroxytrimethylsilane

I-2

OECD 209 and ISO 1892

ASRI

 

2

Uncertain

6670

 

031795-24-1

Potassium methylsilanetriolate

I-2

OECD 209

ASRI

 

1a

3 h

 

EC10 >100 mg/l

139147-73-2

Silane, dichlorodicyclopentyl-

I-2-D-C

OECD 209

ASRI

 

1a

3 hr

>100

 

000124-70-9

Dichloro(methyl)(vinyl)silane

I-2-D-C

OECD 209

ASRI

 

1a

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)

 

1a/1a/2c (WOE)

3hr; 3hr; 3hr (WOE)

>water solubility; >water solubility; >water solubility (WOE)

 

001000-50-6

Butylchlorodimethylsilane

I-2-M-C

88/302/EC

ASRI

 

1a

3h

>340

 

013154-25-1

Chlorotri(3-methyl-propyl)silane

I-2-M-C

OECD 209

ASRI

 

2b

3 hr

>1000 (nominal, parent)

100 (nominal, parent)

005894-60-0

Trichloro(hexadecyl)silane

I-2-T-C

OECD 209

ASRI

 

1a

3h

>1000

≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate

000075-94-5

Trichloro(vinyl)silane

I-2-T-C

OECD 209

ASRI

 

1a

3hr

>100 mg/l

 

001185-55-3

Trimethoxy(methyl)silane

I-2-T-Et-H

OECD 209

ASRI

 

1a

3hr

>100 mg/l

EC10 >100 mg/l

017980-47-1

Triethoxyisobutylsilane

I-2-T-Et-M

OECD 209

ASRI

 

1a

3h

>1000mg/l

≥1000 mg/l

002943-75-1

Triethoxyoctylsilane

I-2-T-Et-M

OECD 209

ASRI

 

1a

3 hr

>1000

1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate

016068-37-4

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

1c

16 h

>8000 mg/l

8000 mg/l

035435-21-3

Triethoxy(2,4,4-trimethylpentyl)silane

I-2-T-Et-M

OECD 209

ASRI

 

1a

3hr

>100 mg/l

 

087135-01-1

1,6-Bis(trimethoxysilyl)hexane

I-2-T-Me-H

OECD 209

ASRI

 

1a

3h

>1000 mg/l

 

016415-12-6

Hexadecyltrimethoxysilane

I-2-T-Me-H

OECD 209

ASRI

 

1a

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

 

1a

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 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 is reported in secondary literature (Union Carbide) for the hexamethyldisilazane. However, the original reference was not available for review and the reliability of this result is not assignable.