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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
Study period:
2009-09-03 to 2009-09-03
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
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
53 µl of the 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: The sludge was coarsely sieved to remove large particles. The sludge was then washed by centrifuging at 1000 g for 10 minutes. The supernatant was decanted and replaced with ISO-medium. The washing step was performed three times. The pH was 7.7 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic sewage feed was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

- Initial biomass concentration: 3.8 g/L
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Post exposure observation period:
Oxygen consumption was measured and recorded for approximately 10 minutes.
Test temperature:
19.9-20.3°C
pH:
8.2 to 8.3
Nominal and measured concentrations:
100 mg/l (loading rate). Performance of a limit concentration at 100 mg/l is acceptable, because 100 mg/l exceeds the expected concentration in a Sewage Treatment Plant.
Details on test conditions:
Test vessel:
- Material, size, headspace, fill volume: glass, 300ml oxygen bottles, 1L test bottles

- Aeration: continuous

- No. of vessels per concentration (replicates): two

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

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)


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
After the 3-hour contact time, a well mixed sample of the contents of the reaction mixture was poured into a 300 ml oxygen bottle, and the flask was sealed with an oxygen electrode connected to a recorder, forcing the air out of the vessel. WTW inolab Oxi 730 supplied with a WTW CellOx 325 oxygen electrode, electrolyte type ELY/G

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 100 mg/L only, tested in duplicate

- Justification for using less concentrations than requested by guideline: No significant inhibition of respiration rate of the sludge was recorded for the test substance at a loading rate of 100 mg/L in both replicates and therefore no further testing was required.
Reference substance (positive control):
yes
Remarks:
(3,5-Dichlorophenol)
Key result
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
The two controls had a difference in respiration rate of 6%, which is less than the 15% limit required by the guideline for a valid study.
Results with reference substance (positive control):
A positive control test with 3, 5-dichlorophenol yielded an EC50 of 8.7 mg/L, which is within the accepted range of 5 to 30 mg/l required by the guideline for a valid study.

Table 1: Results of the activated sludge respiration inhibition test

Test sample

Loading rate (mg/l)

Oxygen conc. at start (mg O2/l)

Oxygen consumption (mg O2/l/h)

% Inhibition

respiration rate

pH

 

 

Initial control

0

7.3

34

-

8.3

Final control

0

6.5

32

-

8.2

Trimethoxy(methyl)silane replicate (1)

100

7.1

33

0

8.3

Trimethoxy(methyl)silane replicate (2)

100

7.1

31

6

8.3

 

 

3,5-dichlorophenol

5

-

-

38

-

12

-

-

59

-

30

-

-

72

-

 

 

Validity criteria fulfilled:
yes
Conclusions:
An activated sludge respiration inhibition 3hr EC10 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.

Description of key information

Toxicity to microorganisms: ASRI 3 hour EC10 >100 mg/L (loading rate) (OECD 209), read-across from a structurally-related substance.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
100 mg/L

Additional information

There are no reliable microorganism toxicity data available for trichloro(propyl)silane (CAS 141-57-1), therefore good quality data for the analogous substance, trimethoxy(methyl)silane (CAS 1185-55-3), have been read across. The submission substance, trichloro(propyl)silane, hydrolyses very rapidly in contact with water to form propylsilanetriol and hydrochloric acid. The read-across substance, trimethoxy(methyl)silane hydrolyses rapidly in contact with water to form methylsilanetriol and methanol. Both substances hydrolyse rapidly and share the same structurally similar silanol hydrolysis products; propylsilanetriol and methylsilanetriol respectively. In view of the very rapid hydrolysis, it is the silanol hydrolysis product that is relevant for environmental risk assessment.

Methanol does not have adverse effects on microorganisms (OECD 2004).

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(propyl)silane (CAS 141-57-1) and trimethoxy(methyl)silane (CAS 1185-55-3) 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 of substances containing a number of different functional groups but specific read-across is between substances with similar functionality.

The table below presents microorganism toxicity data for substances relevant to trichloro(propyl)silane (CAS 141-57-1).

It is considered valid to read-across the results for trimethoxy(methyl)silane (CAS 1185-55-3) 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

124-70-9

Dichloro(methyl)(vinyl)silane

>100 mg/l

EC10 >100 mg/l

OECD 209

ASRI

 

3 h

1

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 hr

2

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

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

 

In the study with trimethoxy(methyl)silane (CAS No. 1185-55-3), an activated sludge respiration inhibition 3h EC10value of >100 mg/L was reported.

References:

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18-20 October 2004, Methanol, CAS 67-56-1

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