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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:
22 March 2007
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Study has been performed according to OECD and/or EU guidelines and according to GLP principles.
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
see below
Qualifier:
according to
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Deviations:
yes
Remarks:
see below
Qualifier:
according to
Guideline:
ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)
Deviations:
not applicable
Principles of method if other than guideline:
Deviation:
The amount of suspended solids in the sludge was just above the range given in the Protocol (4 g/l ± 10%). Evaluation: This did not affect the respiration rate of the sludge, given the results of the control vessels. The study integrity was not adversely affected by this deviation.
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
not required
Vehicle:
no
Details on test solutions:
Since the test substance was sufficiently soluble, a stock solution of 500 mg/l was prepared by adding 125.4 mg test substance to 250 ml of Milli-RO water (tap water purified by reverse osmosis). A magnetic stirring period of 10 minutes was used to accelerate dissolution and to ensure homogeneity. Volumes of the stock solution corresponding to the test concentration were then added to the test media.
A concentration of 100 mg/l, corresponding to 100 ml of the prepared stock solution in 500 ml final volume, was tested in duplicate.
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 (4.47 g/l of sludge, as used for the test). The pH was 7.2 on the day of sampling and 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.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Post exposure observation period:
After the exposure period, oxygen consumption was measured and recorded for approximately 10 minutes. Measurement of pH.

Hardness:
Not applicable.
Test temperature:
18.7 - 19.6 °C
pH:
8.0 - 8.2

Dissolved oxygen:
Oxygen consumption was measured and recorded for approximately 10 minutes. 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 2.5 and 6.5 mg O2/l.
Salinity:
Not applicable
Nominal and measured concentrations:
Loading rate of 100 mg/l

Details on test conditions:
TEST SYSTEM
- Test vessel: All glass, approximately 300 ml oxygen bottles and 1 litre test bottles.
- Type (delete if not applicable): open
- Aeration: continuously with clean, oil-free air
- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates):Two controls without test substance were tested in each test series, one at the start and one at the end.
- Biomass loading rate: 200 ml activated sludge (4.47 g/l suspended solids) in 500 ml final volume

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Milli-RO / Milli-Q 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) : 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 2.5 and 6.5 mg O2/l.
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
Key result
Duration:
3 h
Dose descriptor:
NOEC
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:
No significant inhibition of respiration rate of the sludge was recorded at 100 mg Ditetrahydrofurylpropane per litre. The duplicate measurement confirmed the result of the first measurement (negative values of inhibition were recorded). Therefore, no further testing was needed.
Results with reference substance (positive control):
The EC50 of 3,5-dichlorophenol was in the accepted range of 5-30 mg/l (8.8 mg/l).

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this present test, Ditetrahydrofurylpropane was not toxic to waste water (activated sludge) bacteria at a concentration of 100 mg/l.

Description of key information

A study was conducted according to OECD 209. No significant inhibition of respiration rate of the sludge was recorded at 100 mg Ditetrahydrofurylpropane per litre (NOEC). The duplicate measurement confirmed the result of the first measurement (negative values of inhibition were recorded).

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
100 mg/L

Additional information

Under the conditions of this present test, Ditetrahydrofurylpropane was not toxic to waste water (activated sludge) bacteria at a concentration of 100 mg/L (NOEC). The EC50 was > 100 mg/L.