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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
2009-11-12 to 2009-12-16
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP. The study is considered to be reliability 1 (reliable without restrictions); the read across of the result is considered to be reliability 2 (reliable with restrictions).
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: Known volume of test substance, Milli-RO water, synthetic sewage feed (16 ml) and activated sludge (200 ml) were mixed and made up to 500 ml with Milli-RO water in a 1 litre bottle.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Preparation of inoculum for exposure: Coarsely sieved then washed by centrifuging at 1000 g for 10 minutes and supernatant decanted and replced with ISO-medium. Washing step performed three times.

- Amount suspended solids: 4.0 g/l
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.
Test temperature:
Experiment 1: between 19.4 and 20.0°C; Experiment 2: between 18.5 and 19.4°C.
pH:
Experiment 1: between 6.8 and 6.9; Experiment 2: between 2.0 and 7.2.
Dissolved oxygen:
Oxygen concentration at start (=~ mg O2/l). Experiment 1: 6.2 to 6.7; Experiment 2: 7.7 to 9.6.
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: All glass, approximately 300 ml oxygen bottles and 1 litre test bottles.
- Aeration: Strong aeration with clean, oil-free air.

- No. of vessels per concentration (replicates): Experiment 1: Loading rate tested in duplicate. Experiment 2: Five loading rates.

- No. of vessels per control (replicates): Experiment 1 and 2. Control vessels in duplicate at beginning and end of each series (test substance and reference substance).

- No. of vessels per reference (replicates): Experiment 1 and 2. Three concentrations.


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.).

OTHER TEST CONDITIONS
- Adjustment of pH: None

Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
160 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
32 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
25% inhibition of respiration rate of the sludge was recorded at 100 mg/l, therefore a second experiment was performed with a range of loading rates (10 to 1000 mg/l). The inhibition at a loading rate of 100 mg/l was slightly lower in the second experiment than in the first experiment. No significant inhibition was recorded at and below a loading rate of 32 mg/l. Almost complete inhibition was recorded at and above a loading rate of 320 mg/l. It is likely that the inhibition was influenced by the low pH levels at the higher loading rates, which dropped to pH 3.5 and pH 2.0 at 320 and 100 mg/l respectively (pH at 100 mg/l was 6.8 - 6.9 in both experiments).
Results with reference substance (positive control):
- Results with reference substance valid? Yes. The 3-hr EC50 was in the accepted range of 5-30 mg/l (7.7 mg/l in Experiment 1; 6.1 mg/l in Experiment 2.)

Table 1: Experiment 1. Controls (C) and Dichloro(methyl)silane (T): pH, oxygen concentration, oxygen consumption and percentage inhibition of the respiration rate.

Flask

Loading rate (mg/l)

Oxygen conc. At the start (=~ mg/O2/l)

Oxygen consumption

(mg O2/l/h)

% Inhibition

respiration rate

pH

Cstart T

0

6.9

60

-

7.5

Cend T

0

6.4

68

-

7.4

 

∆13%

 

 

T1

100

6.2

48

25

6.9

T2

100

6.7

48

25

6.8

 

Table 2: Experiment 2. Controls (C) and Dichloro(methyl)silane (T): pH, oxygen concentration, oxygen consumption and percentage inhibition of the respiration rate.

Flask

Loading rate (mg/l)

Oxygen conc. At the start (=~ mg/O2/l)

Oxygen consumption

(mg O2/l/h)

% Inhibition

respiration rate

pH

Cstart T

0

8.1

40

-

7.2

Cend T

0

7.9

43

-

7.1

 

∆8%

 

 

T1

10

7.7

41

1

7.2

T2

32

7.7

39

6

7.0

T3

100

7.8

37

11

6.8

T4

320

9.3

1

98

3.5

T5

1000

9.6

0

100

2.0

 

 

Validity criteria fulfilled:
yes
Conclusions:
An EC50 of 160 mg/l and a NOEC of 32 mg/l for toxicity to microorganisms were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP. It is likely that the inhibition was influenced by the low pH levels at the higher loading rates, but the pH at the NOEC was 7, and therefore the NOEC is considered the most useful and representative result.

Description of key information

No toxicity to STP microorganisms is to be expected

Key value for chemical safety assessment

Additional information

There are no microorganism toxicity data available fortriethoxysilane; therefore, good quality data for the structurally-related substance,dichloro(methyl)silane (CAS No. 75-54-7), have been read across. Both substances hydrolyse to structurally-related silanol hydrolysis products, dimethylsilanetriol andsilanetriol, respectively. It is therefore considered valid to read-across the results for dichloro(methyl)silane (CAS No. 75-54-7) to fill the data gap for the registered substance.

Triethoxysilane and dichloro(methyl)silaneare within a wideranalogue group than the triethoxysilanes analogue group discussed in Section 1.4. Substances within this wider analogue group, in general, exhibit no evidence of significant toxicity to microorganisms.

This wider analogue group for the toxicity to microorganisms endpoint consists of a number of sub-classes of substances. Read-across is carried out between substances with the same sub-class in most cases but in this case the read across substance dichloro(methyl)silaneis part of the sub-class dichlorosilanes structural class (I-2-D-C) and the registered substance is part of the sub-class (I-2-T-Et-H) buth sub classes are included in the wider analogue group explained in thesupporting report (PFA, 2013j) attached in Section 13 of the IUCLID 5 dossier.

Table 7.4.2 presents microorganism toxicity data available for substances within the sub-class (I-2) of alkoxysilanes, silanols, acetoxysilanes and chlorosilanes, etc, where the Si part is of low-biological reactivity, once any hydrolysis is accounted for.

 

Table7.4.2 Microorganism toxicity data available for substances within sub-class (I-2) of chemicals

CAS

Name

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

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

Guideline Number

Test method

Species

Duration

Reliability

001000-50-6

Butylchlorodimethylsilane

>340

 

88/302/EC

ASRI

 

3h

1a

001066-40-6

Hydroxytrimethylsilane

6670

 

OECD 209 and ISO 1892

ASRI

 

Uncertain

1a

001185-55-3

Trimethoxy(methyl)silane

>100

 

OECD 209

ASRI

 

3hr

1a

031795-24-1

Potassium methylsilanetriolate

>100

 

OECD 209

ASRI

 

3 h

1a

087135-01-1

1,6-Bis(trimethoxysilyl)hexane

>1000

 

OECD 209

ASRI

 

3h

1a

017980-47-1

Triethoxyisobutylsilane

>1000

≥1000

OECD 209

ASRI

 

3h

1a

005894-60-0

Trichloro(hexadecyl)silane

>1000

≥1000

OECD 209

ASRI

 

3h

1a

016415-12-6

Hexadecyltrimethoxysilane

>1000

 

OECD 209

ASRI

 

3 hr

1a

002943-75-1

Triethoxyoctylsilane

>1000

 

OECD 209

ASRI

 

3 hr

1a

016068-37-4

4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane

>8000

8000

DIN 38 412, Part 8 (Pseudomonascell multiplication inhibition test)

growth inhibition test

P. putida

16 h

1c

035435-21-3

Triethoxy(2,4,4-trimethylpentyl)silane

>100

 

OECD 209

ASRI

 

3hr

1a

018395-30-7

Trimethoxy(2-methylpropyl)silane

 

EC10 1.3 ml/l

Huls AG method

oxygen consumption

P. putida

5.8 h

2c -don't use to derive PNEC

142877-45-0

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

>1000

≥1000

OECD 209

ASRI

 

3 hr

1a

013154-25-1

Chlorotri(3-methyl-propyl)silane

>1000

100

OECD 209

ASRI

 

3 hr

2b

126990-35-0

Dicyclopentyldimethoxysilane

>water solubility

 

Weight of evidence of three studies: OECD 209//EU C11/Huls AG method (WOE)

ASRI/ASRI/oxygen consumption P. putida

 

3 hr

1a/1a/2c

139147-73-2

Silane, dichlorodicyclopentyl-

>100

 

OECD 209

ASRI

 

3 hr

1a

000124-70-9

Dichloro(methyl)(vinyl)silane

>100 mg/l

 

OECD 209

ASRI

 

3hr

1a

000075-94-5

Trichloro(vinyl)silane

>100 mg/l

 

OECD 209

ASRI

 

3hr

1a

001067-53-4

Tris(2-methoxyethoxy)vinylsilane

 

EC10 > 2 ml/L

Huls AG method

oxygen consumption

P. putida

5 h

2c -don't use to derive PNEC

002768-02-7

Trimethoxyvinylsilane

 

EC10 1.1 ml/l

Huls AG method

oxygen consumption

P. putida

5 h

2c -don't use to derive PNEC

000075-54-7

Dichloro(methyl)silane

160 mg/l

NOEC of 32 mg/l

OECD 209

ASRI

 

3 h

1a

 

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

An EC50of 160 mg/l and a NOEC of 32 mg/l for toxicity to microorganisms were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test, Desmares-Koopmans 2009). It is likely that the inhibition was influenced by the low pH levels at the higher loading rates, but the pH at the NOEC was 7, and therefore the NOEC is considered the most useful and representative result.The study is considered to be reliability 1 (reliable without restrictions); the read across of the result is considered to be reliability 2 (reliable with restrictions).

It is likely that the test organisms were exposed to the hydrolysis products of the substance. As silanetriol will break down further into inorganic, naturally occurring substances such as silica and silica acid and shows no toxicity it is more appropriate to base the hazard assessment on the other hydrolysis product ethanol. Therefore, the environmental hazard assessment, including toxicity to microorganisms due to water and moisture being present, is based on the properties of the hydrolysis product, ethanol.

PNEC is therefore based on an EC50 of 5800 mg/l for Paramecium caudatum for ethanol (SIDS ethanol, 2004).