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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:
Jun 06 - Dec 02, 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
Version / remarks:
July, 2010
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
The test substance was insufficiently soluble to permit addition via aqueous solution. Individually weighed quantities of test substance were added directly to the appropriate test vessels.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
The activated sludge inoculum was collected from the sludge return line at Pool or Burley Menston sewage treatment works (West Yorkshire, UK), which has a predominantly domestic catchment. The point of collection was to ensure that the activated sludge sample was relatively free of exogenous material.
Preparation and Maintenance
The sludge was transported to the test facility in a closed container with an adequate headspace to prevent the sample becoming anoxic. On arrival at the test facility, the sludge was aerated with a compressed air supply delivered through a suitable distribution device.
The suspended solids concentration was determined gravimetrically following homogenisation and adjusted using dechlorinated tap water to 3 g/L (± 0.3 g/L). The sludge was maintained at 20 ± 2°C with aeration. During storage it was maintained at 20 ± 2°C and fed with synthetic sewage concentrate at a rate of 50 mL/L.
An activated sludge sample that provided the test inoculum for the range-finder test was collected on 7 June 2016, the activated sludge sample that provided the test inoculum for the definitive limit test was collected on 20 July 2016.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
20 ± 2°C
pH:
7.01 - 7.25
Dissolved oxygen:
saturated
Nominal and measured concentrations:
Range Finder: 1, 10, 100 and 1000 mg/L
Definitive Limit: 1, 10, 100 and 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: ca 250 mL glass conical flask
- Type (delete if not applicable): open
- Aeration:compressed air supply
- No. of vessels per concentration (replicates): range finder: 2, definitive: 3
- No. of vessels per control (replicates): range finder: 1, definitive: 1
- No. of vessels per vehicle control (replicates): range finder: 4, definitive: 1
- Sludge concentration (weight of dry solids per volume): 3 g/L
- Weight of dry solids per volume of reaction mixture per unit of time:
- Nutrients provided for bacteria: no
- Nitrification inhibitor used (delete if not applicable): N-allylthiourea
- Biomass loading rate:
TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated tap water
- Particulate matter:
OTHER TEST CONDITIONS
- Adjustment of pH: yes

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
TEST CONCENTRATIONS
- Spacing factor for test concentrations: 10
- Justification for using fewer concentrations than requested by guideline: n.a.
- Range finding study yes
- Test concentrations: 1, 10, 100, 1000 mg/L
- Results used to determine the conditions for the definitive study: range finding results
Reference substance (positive control):
yes
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
1 000 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
1 000 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
inhibition of heterotrophic respiration
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
1 000 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
inhibition of respiration due to nitrification
Results with reference substance (positive control):
3,5-DCP:
Total Respiration: 10.1 mg/L
Nitrification Respiration: 3.3 mg/L
Validity criteria fulfilled:
yes
Conclusions:
There was no statistically significant inhibition of respiration observed during the test. The EC50 for the test item was greater than 1000 mg/L under these test conditions.
The NOEC value was determined to be 1000 mg/L, the highest concentration tested.

Description of key information

OECD 209 study (Reliability 1): NOEC = 1000 mg/L

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information