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Toxicity to microorganisms

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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:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes
Analytical monitoring:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The synthetic sewage feed (16 ml) and an adequate amount of the test substance loading were mixed and made up to 250 ml with Milli-RO water in a 1 litre bottle. The pH was determined. Thereafter 250 ml activated sludge was added. This was the start of the test. The mixture was then aerated during the contact time, using a pipette as an aeration device.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Preparation of inoculum for exposure: Coarsely sieved then washed and diluted with ISO medium.

- Amount suspended solids: 3.0 g/l of sludge, as used for the test
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Post exposure observation period:
Oxygen consumption measured and recorded for approximately 10 minutes.After the 3-hour contact time the oxygen consumption was recorded for a period approximately 10 minutes. However, a longer measuring and recording period was allowed. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer.
Determination of oxygen was performed with oxygen probes connected to a BlueBox, a multichannel measuring and controlling system.
Test temperature:
18.7 - 22.0°C
pH:
The pH in all test series, before addition of sludge remained within the range of 7.5 ± 0.5 (7.3-7.5). After the 3 hour exposure period the pH increased to a maximum of 8.2.
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: All glass bottles/vessels.
- Aeration: Clean, oil-free air.

- No. of vessels per concentration (replicates): Loading rates of 10, 100 and 1000 mg/l. The highest loading rate was tested in triplicate, lower loading rates consisted of one replicate.

- No. of vessels per control (replicates): Blank control: three replicates. Also, abiotic control and the highest loading rate with a nitrification inhibitor were tested.

- No. of vessels per reference (replicates): Three concentrations, each one replicate.


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q) (Millipore Corp., Bedford, Mass., USA).

OTHER TEST CONDITIONS
- Adjustment of pH: At a loading rate of 100 and 1000 mg/l a significant pH effect was noted. Since, it is preferred that test solutions have a neutral pH, the pH was adjusted to pH 7.5 ± 0.5 with 1 N NaOH. According to the information of the sponsor, there was no indication that chemical properties of the test substance were changed with pH adjustment (this has been done in former tests with other chlorosilanes).

Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
There was no oxygen uptake from abiotic processes and the results at 1000 mg/l with a nitrification inhibitor showed that the heterotrophic inhibition of the respiration rate was in general comparable to the total inhibition.
Results with reference substance (positive control):
- Results with reference substance valid? Yes. The EC50 of 3,5-dichlorophenol was in the accepted range of 2 to 25 mg/l for total respiration. The controls oxygen uptake rate exceeded 20 mg oxygen per one gram of activated sludge (dry weight of suspended solids) in an hour. The coefficient of variation of oxygen uptake in control replicates did not exceed 30% at the end of the definitive test.

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 rate

(mg O2/l/hr)

% Inhibition

respiration rate

C1

0

59

-

C2

0

57

-

C3

0

42

-

Mean

53

-

SD

9

 

Coefficient of variation (%)

18

 

 

C-N1 (with ATU)

7.5

27

7.5

 

T1

10

45

15

T2

100

57

-8

T3 (mean of three replicates)

1000

50

4

 

T3 (abiotic)

1000

1

98

T3 (with ATU)

1000

33

18

 

Reference substance

5

36

32

Reference substance

12

20

62

Reference substance

30

17

68

Validity criteria fulfilled:
yes
Conclusions:
An EC50 of >1000 mg/l and a NOEC of >=1000 mg/l for toxicity to microorganisms were 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 hour EC50 >1000 mg/L (loading rate) and NOEC >=1000 mg/L (loading rate), based on read-across from a structurally-related substance.

Key value for chemical safety assessment

Additional information

There are no microorganism toxicity data available for ltrichloro(octyl)silane, therefore good quality data for the structurally-related substance trichloro(hexadecyl)silane (CAS 5894-60-0), have been read across. Both substances hydrolyse very rapidly to structurally-related hydrolysis products, octylsilanetriol and hexadecylsilanetriol respectively. The other hydrolysis product for both substances is hydrochloric acid. 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.

Trichloro(octyl)silane and trichloro(hexadecyl)silane are within a wider 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 trichloro(octyl)silane. It is considered valid to read-across the results for trichloro(hexadecyl)silane (CAS 5894-60-0) 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 7.4.2: Microorganism toxicity data for other relevant substances

CAS

Name

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

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

Guideline Number

Test method

Species

Duration

Reliability

1000-50-6

Butylchlorodimethylsilane

>340

 

88/302/EC

ASRI

 

3h

1

1066-40-6

Hydroxytrimethylsilane

6670

 

OECD 209 and ISO 1892

ASRI

 

Uncertain

1

1185-55-3

Trimethoxy(methyl)silane

>100

 

OECD 209

ASRI

 

3hr

1

31795-24-1

Potassium methylsilanetriolate

>100

 

OECD 209

ASRI

 

3 h

1

87135-01-1

1,6-Bis(trimethoxysilyl)hexane

>1000

 

OECD 209

ASRI

 

3h

1

17980-47-1

Triethoxyisobutylsilane

>1000

≥1000

OECD 209

ASRI

 

3h

1

5894-60-0

Trichloro(hexadecyl)silane

>1000

≥1000

OECD 209

ASRI

 

3h

1

16415-12-6

Hexadecyltrimethoxysilane

>1000

 

OECD 209

ASRI

 

3 hr

1

2943-75-1

Triethoxyoctylsilane

>1000

 

OECD 209

ASRI

 

3 hr

1

35435-21-3

Triethoxy(2,4,4-trimethylpentyl)silane

>100

 

OECD 209

ASRI

 

3hr

1

18395-30-7

Trimethoxy(2-methylpropyl)silane

 

EC10 1.3 ml/l

Huls AG method

oxygen consumption

P putida

5.8 h

2

142877-45-0

Silane, trimethoxy(1,1,2-trimethylpropyl)-

>1000

≥1000

OECD 209

ASRI

 

3 hr

1

13154-25-1

Chlorotri(3-methyl-propyl)silane

>1000

100

OECD 209

ASRI

 

3 hr

2

126990-35-0

Dicyclopentyldimethoxysilane

>water solubility

 

OECD 209//EU C11/Huls AG method (WOE)

ASRI/ASRI/

oxygen consumption

P. putida

3 hr

1/1/2

139147-73-2

Silane, dichlorodicyclopentyl-

>100

 

OECD 209

ASRI

 

3 hr

1

124-70-9

Dichloro(methyl)(vinyl)silane

>100 mg/l

 

OECD 209

ASRI

 

3hr

1

75-94-5

Trichloro(vinyl)silane

>100 mg/l

 

OECD 209

ASRI

 

3hr

1

1067-53-4

Tris(2-methoxyethoxy)vinylsilane

 

EC10 > 2 ml/L

Huls AG method

oxygen consumption

P. putida

5 h

2

2768-02-7

Trimethoxyvinylsilane

 

EC10 1.1 ml/l

Huls AG method

oxygen consumption

P putida

5 h

2


In the study with trichloro(hexadecyl)silane, an activated sludge respiration inhibition, 3 hour EC50 value of >1000 mg/L (loading rate) and a NOEC value of >=1000 mg/L (loading rate) were determined in a reliable study conducted according to an appropriate test method and in compliance with GLP.

Reference:

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