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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:
27 January 2012 - 27 January 2012
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: This study has been performed according to OECD and/or EC guidelines and according to GLP principles
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Deviations:
no
Qualifier:
according to
Guideline:
ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
The batch of Tetramethyldivinyldisiloxane tested was a clear colourless liquid with a purity of 98.021±0.002% (n=3). Since Tetramethyldivinyldisiloxane may have the potential to be volatile (information obtained by the sponsor), the test substance was pipetted below the surface of Milli-RO-water (200 ml, tap water purified by reverse osmosis) and stirred briefly to mix (5 minutes) in closed dark brown bottles. The initial loading rates were 2.5 times the final loading rate. Subsequently, 16 ml synthetic medium, 250 ml sludge and Milli-RO water up to 500 ml were added resulting in the required loading rates. Optimal contact between the test substance and test organisms was ensured applying continuous aeration and stirring.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105°C to determine the amount of suspended solids (3.0 g/l of sludge, as used for the test). The pH was 7.9 on the day of testing. The batch of sludge was used one day after collection; therefore 50 ml of synthetic medium was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Post exposure observation period:
After the 3-hour contact time, the oxygen consumption was recorded for a period of approximately 10 minutes. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer. The pH and temperature were determined in the remaining part of the reaction mixture.
Test temperature:
Between 18.5 and 21.8°C
pH:
Before addition of sludge : 7.6 - 7.7.
After the 3 hour exposure period : 7.4 - 8.5.
Dissolved oxygen:
The oxygen concentration at the start of measurements was at least 7.1 mg O2/l.

Oxygen consumption:
Controls: 42 mg O2/l h (mean value).
Tetramethyldivinyldisiloxane 10 mg/l: 45 mg O2/l h.
Tetramethyldivinyldisiloxane 100 mg/l: 52 mg O2/l h.
Tetramethyldivinyldisiloxane 1000 mg/l: 50 mg O2/l h (mean value).
Nominal and measured concentrations:
Nominal loading rates: 10, 100 and 1000 mg/l.
Details on test conditions:
TEST SYSTEM
- Type (delete if not applicable): open
- Material, size, headspace, fill volume: All glass
- Aeration: During exposure with clean, oil-free air
- No. of vessels per concentration (replicates): 1 for 10 and 100 mg/l and 3 for 1000 mg/l
- No. of vessels per control (replicates): 6
- Biomass loading rate: 1.5 g/l suspended solids in final test mixture

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Tap-water purified by reverse osmosis (Milli-RO
EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : The respiration rate from each vessel, in mg O2/l/hr, was calculated from the linear part of the respiration curve, which was generally between 2 and 7 mg O2/l.

TEST CONCENTRATIONS
- Test concentrations: combined limit/range-finding test at 10, 100 and 1000 mg/l (loading rates).
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
(loading rate)
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
(loading rate)
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
In the combined limit/range-finding test no inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg Tetramethyldivinyldisiloxane per litre.

There was no significant oxygen uptake from abiotic processes and the results at 1000 mg/l with a nitrification inhibitor showed no heterotrophic inhibition of the respiration rate.

Results with reference substance (positive control):
The EC50 of 3,5-dichlorophenol was in the accepted range of 2 to 25 mg/l for total respiration (7.6 mg/l).
Reported statistics and error estimates:
ECx
For the reference substance the percentage inhibition was plotted against the logarithm of the concentrations and the EC50 was determined using linear regression analysis.

For Tetramethyldivinyldisiloxane no EC50 could be calculated because the test substance proved to be non-toxic (EC50 > a loading rate of 1000 mg/l).

NOEC estimation
No statistical analysis of the data was performed as no inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg Tetramethyldivinyldisiloxane per litre.
Validity criteria fulfilled:
yes
Conclusions:
A 3 hour ASRI EC50 value of >1000mg/l and NOEC value of ≥ 1000 mg/l 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: 3 hour ASRI EC50 >1000 mg/l; NOEC ≥1000 mg/l.

Key value for chemical safety assessment

Additional information

A 3 hour ASRI EC50 value of >1000 mg/l and NOEC value of ≥1000 mg/l were determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP (Desmares-Koopmans, 2012).