Dichlorocyclohexylmethylsilane

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:

1997-05-12 to 1997-08-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

Aqueous emulsions were stirred for 30 minutes at room temperature in the dark to reach the practically achievable maximum concentration of dissolved test substance up to the limit of solubility, and in case of an excess of test substance, to reach the saturation equilibrium.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

Aerobic activated sludge from a domestic waste water treatment plant (ARA Ergolz II, Fullinsdorf/ Switzerland).
The sludge was washed by centrifugation, the supernatant liquid phase decanted, the solid material resuspended in tap water and again centrifuged. This procedure was repeated twice. An aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet sludge to its dry weight determined. Based on this ratio calculated, aliquot of washed sludge suspension were made up with Soerensen buffer (pH 7), to obtain a concentration equivalent to 2 g dry weight basis per litre. To this mixture, 50 ml synthetic sewage feed per litre was added daily starting four days prior to use, and the sludge was kept at room temperature under continuous aeration until use. Immediately before use, the dry weight of activated sludge was determined to be 5.2 g/l, and diluted with tap water to a dry weight of 4 g/l. The pH was adjusted to 7.8 with 0.5 mol/l sulfuric acid.

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

22°C

pH:

8.3 - 8.5

Dissolved oxygen:

During aeration the oxygen concentration did not drop below 4.0 mg O2/l and was at least 6.5 mg O2/l prior to measurement of oxygen consumption.

Nominal and measured concentrations:

Nominal concentrations 6, 12, 24, 50, 100 mg/l.

Details on test conditions:

TEST SYSTEM
- Test vessel: 1000 ml brown glass flasks. Filled to 500 ml final volume.

- Aeration: Aeration using compressed air at an air-flow rate of approximately one litre per minute.

- No. of vessels per concentration (replicates): 5 test substance, 4 reference substance

- No. of vessels per control (replicates): 2

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : After exactly three hours incubation, the first flask (inoculum control flask 1) was taken for measurement of the oxygen consumption over a period of up to ten minutes. Thereafter, the oxygen consumption was measured in the rest of the test flask in 10 minute intervals. For measurement of respiration rate the samples were transferred into Winkler flasks. The reduction of the oxygen concentration was measured with an oxygen electrode and was continuously recorded by means of a curve for up to about ten minutes. During measurement, the samples were not aerated but continuously stirred on a magnetic stirrer. The apparatus used for oxygen measurements was the WTW OXI 539 meter.

Reference substance (positive control):

yes

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Results with reference substance (positive control):

EC50 19.6 mg/l. Therefore it is in the range of 5 to 30 mg/l recommended by the test guideline, thus confirming suitability of the activated sludge.

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

Flask	Nominal concentration (mg/l)	Oxygen consumption (mg O2/l/min)	% Inhibition respiration rate
Control 1	0	0.935	-
Control 2	0	1.004	-
Mean		0.970
Test substance	100	0.976	-0.7
Test substance	50	1.061	-9.4
Test substance	24	0.979	-1.0
Test substance	12	1.029	-6.1
Test substance	6	1.066	-10.0
Reference substance 1	100	0.094	90.3
Reference substance 2	32	0.198	79.6
Reference substance 3	10	0.778	19.8
Reference substance 4	3.2	0.975	-0.6

 

Validity criteria fulfilled:

yes

Conclusions:

An activated sludge respiration inhibition 3hr EC50 value of >100 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 100 mg/l.

Description of key information

Toxicity to microorganisms: ASRI 3 hour EC50 >100 mg/L (loading rate) (OECD 209), read-across from a structurally-related substance.

Key value for chemical safety assessment

EC50 for microorganisms:

100 mg/L

Additional information

There are no microorganism toxicity data available for dichloro(cyclohexyl)methylsilane (CAS 5578-42-7), therefore good quality data for the structurally-related substance dicyclopentyldichlorosilane (CAS 139147-73-2), have been read across. Both substances hydrolyse very rapidly to structurally-related hydrolysis products, cyclohexyl(methyl)silanediol and dicyclopentylsilanediol respectively. The other hydrolysis product is hydrochloric acid for both substance. 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.

Dichloro(cyclohexyl)methylsilane (CAS 5578-42-7) and dicyclopentyldichlorosilane (CAS 139147-73-2) are within a group of substances within which in general, there is no evidence of significant toxicity to microorganisms. This group consists of substances containing a number of different functional groups but specific read-across is between substances with similar functionality.

Table 7.4.2 presents microorganism toxicity data available for substances relevant to dichloro(cyclohexyl)methylsilane. It is considered valid to read-across the results for dicyclopentyldichlorosilane (CAS 139147-73-2) to fill the data gap for the registered substance since the source and target substances generate structurally analogous silanol hydrolysis products.

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

Table: Microorganism toxicity data for relevant substances

CAS	Name	Result: E(I)C50 (mg/l)	Result: NOEC (or EC10/ EC20) (mg/l)	Guideline	Test method	Species	Duration	Klimisch code
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
5894-60-0	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		3h	1
1185-55-3	Trimethoxy(methyl)silane	>100 mg/l	EC10 >100 mg/l	OECD 209	ASRI		3h	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		3h	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 h	1

 

In the study with dicyclopentyldichlorosilane (CAS 139147-73-2), an activated sludge respiration inhibition 3 hour EC₅₀ value of >100 mg/L was reported.

Reference:

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