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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: According to the OECD activated sludge, respiration inhibition test, limited information on test substance review artcile, non-GLP.
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
GLP compliance:
not specified
Analytical monitoring:
not specified
Details on sampling:
- Concentrations: 0.5 to 5.0 g/L
- Sampling method: Stock solutions of the test chemicals were prepared in deionized water prior to inhibition testing.
- Sample storage conditions before analysis: Fresh stock solution was prepared as required and stored for not more than two days at 5℃.
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Stock solutions (0.5 to 5.0 g/L) of the test chemicals were prepared in deionized water prior to inhibition testing.
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): deionized water

No additional data
Test organisms (species):
activated sludge
Details on inoculum:
- Laboratory culture: On return to the laboratory, the solids were allowed to settle and the waste liquor was discarded.
- Method of cultivation: The solids were then transferred into a 9 L laboratory-scale, semi-continuous activated sludge cylider and diluted to approximately 8.5 L with deionized water. The system was initially mixed by aerating at a rate of approximately 0.5 L/min, and the concentration of mixed liquor suspended solids was determined by gravimetric analysis. The solids were then allowed to settle in the cylinder and the upper layer of waste liquor was discarded. The activated sludge was washed three times with appropriate volumes of deionized water. After washing, the system was adjusted to contain 4000±400 mg of mixed liquor suspended solids per liter. The system was then aerated continuously at a rate of 0.5 L/min and incubated at ambient temperature (21℃). The system was supplemented daily with 50 mL of a synthetic sewage stock solution per liter of activated sludge.

No additional data
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Post exposure observation period:
None stated
Hardness:
None stated
Test temperature:
21℃
pH:
7.5±0.5
Dissolved oxygen:
None stated
Salinity:
None stated
Nominal and measured concentrations:
None stated
Details on test conditions:
TEST SYSTEM
- Test vessel: 1 L bottle
- Material, size, headspace, fill volume: 1 L bottle
- Aeration: 0.5-1.0 L/min
- Renewal rate of test solution (frequency/flow rate): Reaction mixtures were typically prepared at 15 minute intervals.

OTHER TEST CONDITIONS
- Adjustment of pH: Prior to inhibition testing, the activated sludge system was adjusted to pH 7.5±0.5 by the addition of H3PO4.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): IC50 values and effects of pH on the respiration rate of activated sludge

No additional data
Reference substance (positive control):
yes
Remarks:
3.5-dichlorophenol
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
740 mg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
O2
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: Graphic analysis
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
757 mg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
O2
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: Moving average Analysis
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
759.3 mg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
O2
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: Probit transformation Analysis 95% CL 707.9-814.7 mg/L
Details on results:
No information provided
Results with reference substance (positive control):
- Results with reference substance valid? Yes
- Relevant effect levels: IC50: 12.2 mg/L, Variance: 18%
Reported statistics and error estimates:
No information provided
Validity criteria fulfilled:
yes
Conclusions:
The IC50 of the test substance is 759 mg/L based on probit analysis of the data.
Executive summary:

This activated sludge respiration inhibition test was conducted according to OECD 209 guideline.

The IC50 of the test substance is 759 mg/L based on probit analysis of the data.

Description of key information

The inhibition of activated sludge bacteria was investigated in a study equivalent to an OECD 209 study. IC50 of 759 mg/L was derived for inhibition to activated sludge respiration.

Key value for chemical safety assessment

EC50 for microorganisms:
759 mg/L

Additional information

Other data were poorly reported and/or on non-standard species.