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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:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
The test water used for the test was deionized reverse osmosis water containing less than 1 mg/L Dissolved Organic Carbon (DOC).
Synthetic Sewage
A synthetic sewage of the following composition, was added to each test vessel to act as a respiratory substrate:
16 g Peptone
11 g Meat extract
3 g Urea
0.7 g NaCl
0.4 g CaCl2.2H2O
0.2 g MgSO4.7H2O
2.8 g K2HPO4
dissolved in a final volume of 1 liter of water with the aid of ultrasonication.
In the range-finding test, the pH of the synthetic sewage stock used to feed the activated sewage sludge was pH 7.2 and the pH of the synthetic sewage stock used for the range-finding test was pH 7.2. The pH values were measured using a Hach HQ40d Flexi handheld meter.
Test organisms (species):
activated sludge
Details on inoculum:
A mixed population of activated sewage sludge micro-organisms was obtained on 19 June 2017 from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK which treats predominantly domestic sewage.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 - 22 C
pH:
7-8
Dissolved oxygen:
5.4-6.0 mg/l
Details on test conditions:
At time "0" 16 mL of synthetic sewage was diluted to 250 mL with water and 250 mL of inoculum added in a 500 mL conical flask (first control). The mixture was aerated with clean, oil-free compressed air via narrow bore glass tubes at a rate of 0.5 to 1.0 liter per minute. Thereafter, at 15 minute intervals the procedure was repeated for the second control followed by the reference item vessels with appropriate amounts of the reference item being added.
Finally two further control vessels were prepared.
The test was conducted under normal laboratory lighting in a temperature controlled room at measured temperatures of between 20 and 22 ºC.
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
> 10 - < 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 100 - < 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Details on results:
No statistically significant toxic effects were shown at the test concentration of 10 mg/L, however statistically significant toxic effects were shown at the test concentrations of 100 and 1000 mg/L.
It was considered unnecessary and unrealistic to test at concentrations in excess of 1000 mg/L.
Results with reference substance (positive control):

The validation criterion for the reference item EC50 value was also satisfied (EC50=6.8 mg/l which is within defined limit 5.2-9.0 mg/l).
Validity criteria fulfilled:
yes
Conclusions:
The effect of the test item on the respiration of activated sewage sludge gave a 3-Hour EC50 value of between 100 and 1000 mg/L. The No Observed Effect Concentration (NOEC) was less than 100 mg/L. It was considered unnecessary and unrealistic to test at concentrations in excess of 1000 mg/L.
Executive summary:

The effect of the test item on the respiration of activated sewage sludge gave a 3-Hour EC50 value of between 100 and 1000 mg/L. The No Observed Effect Concentration (NOEC) was less than 100 mg/L. It was considered unnecessary and unrealistic to test at concentrations in excess of 1000 mg/L.

Description of key information

The effect of the test item on the respiration of activated sewage sludge gave a 3-Hour EC50 value of between 100 and 1000 mg/L. The No Observed Effect Concentration (NOEC) was less than 100 mg/L. It was considered unnecessary and unrealistic to test at concentrations in excess of 1000 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L
EC10 or NOEC for microorganisms:
10 mg/L

Additional information