tert-butylchlorodimethylsilane

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

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: EC Guideline 88/302/EC

GLP compliance:

yes

Analytical monitoring:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Preparation of the inoculum: Activated sludge (approximately 5 l) collected from Marl-ost sewage treatment plant was processed the day of sampling and used. The mud was allowed to settle once and centrifuged at 2000 min-1 three times.

Content of suspended solids: 3.93 g/l (activated sludge). This level gives a concentration of 1.57 g/l in the test medium.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Post exposure observation period:

Oxygen consumption measured over a period of 8 minutes.

Test temperature:

18.0 to 20.7°C

Nominal and measured concentrations:

90.8, 131.4, 173.8, 266.6, 341.4 mg/l (nominal).

Reference substance (positive control):

yes

Remarks:

3, 5 Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 340 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The difference between control 1 and 2 is 2.4% and thus does not exceed the 15% maximum value specified by the guideline.

Results with reference substance (positive control):

EC50 of reference substance was 5.0 mg/l, and thus within the range 5 - 30 mg/l as specified by the guideline.

Table 1: Controls, reference substance (3, 5-dichlorophenol) and test substance: oxygen consumption and percentage inhibition of the respiration rate.

Flask	Oxygen consumption (mg O2/l/hr)	% Inhibition respiration rate
Control (1)	30.83	-
Control (2)	30.08	-
Test substance (341.4 mg/l)	25.95	14.8
Test substance (266.6 mg/l)	28.35	6.9
Test substance (173.8 mg/l)	27.38	10.1
Test substance (131.4 mg/l)	27.92	8.3
Test substance (90.8 mg/l)	28.20	7.4
Reference substance (5 mg/l)	15.32	49.7
Reference substance (15 mg/l)	7.20	76.4
Reference substance (30 mg/l)	3.78	87.6

 

Conclusions:

An activated sludge respiration inhibition 3 hr EC50 value of >340 mg/l was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Toxicity to microorganisms: ASRI 3 hr EC₅₀ >340 mg/l (loading rate) (OECD 209), read-across from a structurally-related substance. The EC₅₀ is equivalent to >298 mg/l when expressed in terms of the silanol hydrolysis product of the tested substance.

Additional information

There are no reliable microorganism toxicity data available for tert-butyl(chloro)dimethylsilane (CAS No. 18162-48-6), therefore good quality data for the analogous substance, butyl(chloro)dimethylsilane (CAS No. 1000-50-6), have been read across. The registration substance, tert-butyl(chloro)dimethylsilane, hydrolyses very rapidly in contact with water to form tert-butyl(dimethyl)silanol and hydrochloric acid. The read-across substance, butyl(chloro)dimethylsilane also hydrolyses very rapidly in contact with water to form butyl(dimethyl)silanol and hydrochloric acid. Both substances hydrolyse very rapidly and share the same structurally similar silanol hydrolysis products; tert-butyl(dimethyl)silanol and butyl(dimethyl)silanol. In view of the very rapid hydrolysis, it is the silanol hydrolysis product that is relevant for environmental risk assessment.

Hydrochloric acid is not expected to have adverse effects on microorganisms in a sewage treatment plant, where the pH is maintained within a favourable range.

tert-Butyl(chloro)dimethylsilane (CAS No. 18162-48-6) and butyl(chloro)dimethylsilane (CAS No. 1000-50-6) are within an analogue group of substances within which, in general, there is no evidence of significant toxicity to microorganisms.

This analogue group for the toxicity to microorganisms 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 microorganism toxicity data for substances within the sub-class I-2. tert-Butyl(chloro)dimethylsilane (CAS No. 18162-48-6) and butyl(chloro)dimethylsilane (CAS No. 1000-50-6)

are members of this sub-class.

It is therefore considered valid to read-across the results for butyl(chloro)dimethylsilane (CAS No. 1000-50-6) to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013j) attached in Section 13.

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

CAS	Name	Result: E(I)C50 (mg/l)	Result: NOEC (or EC10/ EC20) (mg/l)	Guideline	Test method	Species	Duration	Reliability
1066-40-6	Hydroxytrimethylsilane	6670		OECD 209 and ISO 1892	ASRI		uncertain	2
31795-24-1	Potassium methylsilanetriolate		EC10 >100 mg/l	OECD 209	ASRI		3 h	1
139147-73-2	Silane, dichlorodicyclopentyl-	>100		OECD 209	ASRI		3 h	1
124-70-9	Dichloro(methyl)(vinyl)silane	>100 mg/l	EC10 >100 mg/l	OECD 209	ASRI		3 h	1
126990-35-0	Dicyclopentyldimethoxysilane	>water solubility; >water solubility; >water solubility (WOE)		OECD 209/EU C11/Huls AG method (WOE)	ASRI/ASRI/oxygen consumptionP. putida(WOE)		3 h; 3h; 3h (WOE)	1/1/2 -don't use to derive PNEC* (WOE)
1000-50-6	Butylchlorodimethylsilane	>340		88/302/EC	ASRI		3h	1
13154-25-1	Chlorotri(3-methyl-propyl)silane	>1000 (nominal, parent)	100 (nominal, parent)	OECD 209	ASRI		3 h	2
005894-60-0	Trichloro(hexadecyl)silane	>1000	≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate	OECD 209	ASRI		3h	1
75-94-5	Trichloro(vinyl)silane		>100 mg/l	OECD 209	ASRI		3hr	1
1185-55-3	Trimethoxy(methyl)silane	>100 mg/l	EC10 >100 mg/l	OECD 209	ASRI		3hr	1
17980-47-1	Triethoxyisobutylsilane	>1000mg/l	≥1000 mg/l	OECD 209	ASRI		3h	1
2943-75-1	Triethoxyoctylsilane	>1000	≥1000 mg/l Nitrification control indicated no heterotrophic inhibition of respiration rate	OECD 209	ASRI		3 h	1
16068-37-4	4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane	>8000 mg/l	8000 mg/l	DIN 38 412, Part 8 (Pseudomonas cell multiplication inhibition test)	growth inhibition test	P. putida	16 h	1
35435-21-3	Triethoxy(2,4,4-trimethylpentyl)silane	>100 mg/l		OECD 209	ASRI		3hr	1
87135-01-1	1,6-Bis(trimethoxysilyl)hexane	>1000 mg/l		OECD 209	ASRI		3h	1
87135-01-1	1,6-Bis(trimethoxysilyl)hexane	>1000 mg/l		OECD 209	ASRI		3h	1
16415-12-6	Hexadecyltrimethoxysilane	>1000	Nitrification control indicated no heterotrophic inhibition of respiration rate.	OECD 209	ASRI		3 h	1
18395-30-7	Trimethoxy(2-methylpropyl)silane		EC10 1.3 ml/l	Huls AG method	oxygen consumption	P. putida	5.8 h	2 -don't use to derive PNEC*
2768-02-7	Trimethoxyvinylsilane		EC10 1.1 ml/l	Huls AG method	oxygen consumption	P. putida	5 h	2 -don't use to derive PNEC*
142877-45-0	Silane, trimethoxy(1,1,2-trimethylpropyl)-	>1000	≥1000 mg/l	OECD 209	ASRI		3 hr	1

  * Emulsifier nonylphenol ethoxylate propoxylate used. Results should be used with caution. Also, reference substance not used

In the study with butyl(chloro)dimethylsilane (CAS No. 1000-50-6), an activated sludge respiration inhibition 3h EC₅₀ value of >340 mg/l (loading rate) was determined in a reliable study conducted according to an appropriate test protocol and in compliance with GLP. This indicates that the test substance was not toxic to waste water (activated sludge) bacteria at a loading rate of 340 mg/l. The results may be expressed in terms of concentration of the hydrolysis product of the tested substance, butyl(dimethyl)silanol, by applying a molecular weight correction: (MW of silanol = 132.28/ MW of parent = 150.73) * >340 = >298 mg/l.

Reference:

PFA, 2013j, Peter Fisk Associates, STP Microorganism toxicity Main Analogue Group report, PFA.300.003.006