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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:
8th February 2012 to 9th February 2012
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
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
5, 50 and 500 mg test material (in triplicate) were each separately dispersed in approximately 200 mL of deionised reverse osmosis water and subjected to ultrasonication for 15 minutes followed by 24 hours of magnetic stirring. All test vessels were shielded from light during mixing. 16 mL synthetic sewage, 250 mL activated sewage sludge and water were added to a final volume of 500 mL to give three replicates at concentrations of 10, 100 and 1000 mg/L.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Activated sewage sludge from the aeration stage of a sewage treatment plant predominantly treating domestic sewage was maintained on continuous aeration at a temperature of approximately 21 ºC overnight prior to use. On the day of collection, 10 L of activated sewage sludge was fed 500 mL synthetic sewage sludge. The suspended solids was equal to 3 g/L prior to use.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 ± 2 ºC
pH:
7.2-8.2
Dissolved oxygen:
2.0-3.8 mg/L
Nominal and measured concentrations:
10, 100 and 1000 mg/L (as part of a range-finding study)
Details on test conditions:
TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionised reverse osmosis water containing <1 mg/L Dissolved Organic Carbon

TEST CONCENTRATIONS
- Test concentrations: 10, 100 and 1000 mg/L
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
Remarks:
respiration rate
Details on results:
No statistically significant toxic effects were seen at 10 mg/L but statistically significant toxic effects were seen at 100 and 1000 mg/L.
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: EC20 4 mg/L; EC50 11 mg/L; EC80 29 mg/L

Table 1: Oxygen consumption rates and percentage inhibition values

Nominal conc. (mg/L) Initial O2 reading (mg/L) Measurement period (min.) Final O2 reading (mg/L) O2 consumption (mg O2/L/hr) % inhibition
 Control R1 3.7   3  1.5  44.0  -
 Control R2 3.8  3  1.6  44.0  -
 Control R3  3.9  3  1.7  44.0  -
 Control R4  3.8  3  1.5  46.0  -
 Test material 10  3.8  3  1.5  46.0  [3]
  Test material 100  2.8  2  1.5  39.0  12
  Test material 1000 R1  4.1  4  1.8  34.5  22
  Test material 1000 R2  4.2  4  1.8  36.0  19
   Test material 1000 R3  4.6  4  2.2  36.0  19
 3,5-dichlorophenol 3.2  4.4  4  1.8  39.0  12
 3,5-dichlorophenol 10  6.6  10  3.0  21.6  51
 3,5-dichlorophenol 32  8.1  10  6.8  7.8.0  82
Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the test, the effect of the test material on the respiration of activated sewage sludge micro-organisms gave a 3 h EC50 of > 1000 mg/L.
Executive summary:

A GLP study was performed to assess the effect of propargite on the respiration of activated sewage sludge following standard guideline OECD 209. Activated sewage sludge was exposed to an aqueous dispersion of the test material at concentrations of 10, 100 and 1000 mg/L (three replicates for highest concentration) for a period of 3 hours at 20 ± 2 ºC with the addition of a synthetic sewage as a respiratory substrate. The rate of respiration was determined after 3 hours contact time and compared to a control and reference substance. The EC50 was determined to be >1000 mg/L. It was subsequently considered unnecessary to test at concentrations >1000 mg/L.

Description of key information

EC50 > 1000 mg/L; study conducted in accordance with OECD Guideline 209; Clarke, 2012

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L

Additional information

A GLP study was performed to assess the effect of propargite on the respiration of activated sewage sludge following standard guideline OECD 209. Activated sewage sludge was exposed to an aqueous dispersion of the test material at concentrations of 10, 100 and 1000 mg/L (three replicates for highest concentration) for a period of 3 hours at 20 ± 2 ºC with the addition of a synthetic sewage as a respiratory substrate. The rate of respiration was determined after 3 hours contact time and compared to a control and reference substance. The EC50 was determined to be >1000 mg/L. It was subsequently considered unnecessary to test at concentrations > 1000 mg/L.

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