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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:
From 2014-10-23 to 2014-10-31
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
Version / remarks:
Adopted 22 July, 2010
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
- Purity: 100 %
- Lot No.: KNC110310
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: 5.0008 g test item was weighed, dissolved and made up to 500 mL with deionized water. The concentration of the stock solution was 10 g/L.
- Controls: Blank controls were run at the beginning and end of the test with six replicates.
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Preparation of Inoculum:
Fresh activated sludge was collected from Jiangxinzhou city sewage plant before the test. Upon arrival at the laboratory, the sludge was rinsed with dechlorinated water. On the experiment day, 4 samples of 10 mL suspension of the inoculum were transferred to an evaporating dish and dried at 120 ℃ for 3 hours (±0.5 hour). The concentration of suspended solid was 9.28 g SS/L. 3 g SS/L of activated sludge suspended solid was prepared and continuously aerated at 20±2℃ until usage.
- Preparation of Synthetic Sewage Feed:
16.0041 g of peptone, 11.0430 g of beef extract, 3.0048 g of urea, 0.7050 g of NaCl, 0.4031 g of CaCl2∙2H2O, 0.09807 g of MgSO4 and 3.6747 g of K2HPO4∙3H2O were weighed and made up to 1 L with deionized water. The pH of synthetic sewage feed was adjusted to 7.5±0.5.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
20±2℃
Nominal and measured concentrations:
Nominal: 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 1000 mL Glass container filled with 500 mL mixture
- Aeration: yes, gas flow rate: 0.5 L/min- 1 L/min
- No. of vessels per concentration (replicates): 5
- No. of vessels per control (replicates): 6
- No. of vessels per abiotic control (replicates): 3
- Concentrations of activated sludge: 1500 mg SS/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Deionized water

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Details on termination of incubation: After an exposure of 3 hours, each of the samples was transferred into a 250 mL triangular flask to fulfill the flask. Magnetic stirrers were added and an oxygen electrode was inserted into the flask.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): The concentrations of dissolved oxygen were recorded for 10 min in the enclosed flask at the end of exposure.

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: 10, 100, 1000 mg/L
- Results used to determine the conditions for the definitive study:
At the end ofthe test, the percentage inhibitions for each concentration were 4.25 %, 5.88 %, 6.42 %, respectively. The test item had no abiotic oxygen consumption.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Details on results:
At the end ofthe test, the percentage inhibitions for each replicate ofthe test group were 6.74 %, 8.24 %, 5.99 %, 5.37 % and 6.12 %.
The coefficient of variation of oxygen uptake rate at the end of the limit test in blank control replicates was 1.53 %.
The blank controls oxygen uptake rate was 32.0 mg/ (h∙gSS).
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: The 3h-EC50 of the reference item to microorganisms from activated sludge was 10.370 mg/L, while the 95 % confidence limit was 8.607 mg/L ~ 12.212 mg/L
Reported statistics and error estimates:
Statistical software SPSS 17.0 was used for the calculation of EC50 and 95 % confidence limit for test item and reference item.
Validity criteria fulfilled:
yes
Conclusions:
According to the results of limit test, the 3 h-EC50 of the test item on aerobic microorganisms from activated sludge was greater than 1000 mg/L.
Executive summary:

The test was designed to determine the effect of the test item on the respiration rate of aerobic microorganisms in aerobic water environment according to OECD 209.

According to the results of range-finding test, the concentration of 1000 mg/L was designed for the limit test with blank control. Five replicates were made for the test groups while six replicates for the blank control group. Blank control group was run at the beginning and end of the test.

The result showed that the 3h-EC50 of the test item on aerobic microorganisms from activated sludge was greater than 1000 mg/L.

Description of key information

The effect of the test item on the respiration rate of aerobic microorganisms in aerobic water environment was determined according to OECD 209.

The result showed that the 3h-EC50 of the test item on aerobic microorganisms from activated sludge was greater than 1000 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L

Additional information