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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:
2009-09-04 to 2009-09-04
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
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- 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: the sludge was coarsely sieved then washed

- 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. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer.
Test temperature:
18.9-19.8°C
pH:
8.2
Details on test conditions:
TEST SYSTEM

- Test vessel:

- Material, size, headspace, fill volume: glass, 300ml oxygen bottles, 1L test bottles

- Aeration: continuous during the 3 hour test period

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

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

- Biomass loading rate: 100 mg/L


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

- Justification for using less concentrations than requested by guideline: Performance of a limit concentration at 100 mg/l is acceptable, because 100 mg/l exceeds the expected concentration in a Sewage Treatment Plant.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
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
Details on results:
The two controls had a difference in respiration rate of 0%, 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 7.2 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

7.2

34

-

8.4

Final control

0

7.0

34

-

8.3

3-(triethoxysilyl)propiononitrile replicate (1)

100

5.4

47

-38 (a)

8.2

3-(triethoxysilyl)propiononitrile replicate (2)

100

5.4

47

-38 (a)

8.2

 

 

3,5-dichlorophenol

5

-

-

43

-

12

-

-

61

-

30

-

-

67

-

 

Note: (a) A negative value indicates stimulation of the respiration rate of the sludge

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: 3 hour EC50 >100 mg/L (activated sludge respiration inhibition, OECD 209) for analogous substance 3-(triethoxysilyl)propiononitrile.

Key value for chemical safety assessment

Additional information

There are no microorganism toxicity data available for 3-(trimethoxysilyl)propiononitrile, therefore, good quality data for the analogous substance 3-(triethoxysilyl)propiononitrile (CAS 919-31-3) have been read across. Both substances share a common hydrolysis product, 3-(trihydroxysilyl)propiononitrile, and are also expected to hydrolyse to some extent within the timescale of the test. The other hydrolysis products are methanol and ethanol respectively.

Methanol and ethanol do not have adverse effects on microorganisms.

Both 3-(trimethoxysilyl)propiononitrile and 3-(triethoxysilyl)propiononitrile are within an analogue group of substances that 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.

The table below presents microorganism toxicity data available for substances within the sub-class of chlorosilanes, siloxanes, silanes and alkoxysilanes etc, with nitrile functional group(s) in side chain after any very rapid hydrolysis has been accounted for.

3-(Trimethoxysilyl)propiononitrile and 3-(triethoxysilyl)propiononitrile are members of this sub-class.

It is therefore considered valid to read-across the results for 3-(triethoxysilyl)propiononitrile to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013) attached in Section 13.

Table: Microorganism toxicity data available for organosilane substances with nitrile functional group

CAS

Name

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

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

Guideline Number

Test method

Species

Duration

Reliability

919-31-3

3-(Triethoxysilyl)propiononitrile

>100

 

 OECD 209

ASRI

 

3 hours

1

 

An activated sludge respiration inhibition 3hr EC50 value of >100 mg/L (loading rate) was determined for 3-(triethoxysilyl)propiononitrile.