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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:
28-11-1989
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP, well documented and valid.
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes
Analytical monitoring:
no
Vehicle:
yes
Details on test solutions:
The test substance is poorly soluble s in water and therefore was first dissolved in dichloromethane. The test substance in dichloromethane was added to silica gel (100-200 mesh) weighed in a petri-dish. The solvent was allowed to evaporate by placing the petri-dish in a hood for 3 hours, and the entire contents were then transferred to the test erlenmeyers. This method allowed a good contact between the activated sludge and the test substance. Although no toxicity of the silica gel was expected, a control with silica gel was added as well
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Secondary activated sludge was collected from the RZWI Nieuwgraaf in Duiven (1989.11.28). This activated sludge plant predominantly treats domestic wastewater. Prior to use, the activated sludge was diluted with tap water (1. 5x) and homogenized for two minutes in a lab blender 400. The activated sludge concentration in the incubation vessels was 0,6 g dry weight/litre.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
30 min
pH:
7.3-7.7
Nominal and measured concentrations:
62.5, 125, 250, 500, 1000 mg/L nominal
Details on test conditions:
The homogenized activated sludge was incubated in a shaking water bath (100 Hz, 20°C) for 30 minutes with various concentrations of the test compound and synthetic sewage.
Reference substance (positive control):
yes
Remarks:
3.5-dichlorophenol
Duration:
30 min
Dose descriptor:
EC10
Effect conc.:
500 - < 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:
The respiration rates of the activated sludge were measured in a Biological Oxygen Monitor YSI 5300 (Yellow Springs Instruments, Ohio, USA). The BOM consisted of a thermostated vessel with a magnetic stirrer and an oxygen electrode. The vessel is tightly closed by the electrode to measure the oxygen depletion. The volume of the vessel was 10 ml and the temperature in the vessel was 20°C.
Results with reference substance (positive control):
EC 50 ==> 5.0<10 mg/L

A slight inhibition of the respiration rate occurred at 500-1000 mg/L of bis (2,4-dichlorobenzoyl) peroxide/silicone oil onto silica gel. This result shows that the EC10 for activated sludge is 500-1000 mg/litre. This result cannot be interpreted as a normal EC value.

Validity criteria fulfilled:
yes
Conclusions:
Test is valid and well performed/documented. the result however has limitations. The EC10 is determined to be 500-1000 mg/L
Executive summary:

In order to predict effects of chemicals in the environment and in biological wastewater treatment plants, an activated sludge respiration inhibition test was performed. The test. substance was not soluble in water and therefore the activated sludge was exposed to bis (2,4-dichlorobenzoyl) peroxide/silicone oil adsorbed onto silica gel at various concentrations. By this exposure an effect was recorded at 500 and 1000 mg/L. The EC10 for activated sludge is 500-1000 mg/L

Description of key information

One OECD 209 study is available where the EC10 is > 500 mg/L (loading)

Key value for chemical safety assessment

EC50 for microorganisms:
500 mg/L

Additional information

In order to predict effects of chemicals in the environment and in biological wastewater treatment plants, an activated sludge respiration inhibition test was performed. The test. substance was not soluble in water and therefore the activated sludge was exposed to bis (2,4-dichlorobenzoyl) peroxide/silicone oil adsorbed onto silica gel at various concentrations. By this exposure an effect was recorded at 500 and 1000 mg/L. The EC10 for activated sludge is 500-1000 mg/L