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Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1985
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
Principles of method if other than guideline:
not relevant
GLP compliance:
not specified
Analytical monitoring:
yes
Remarks:
See abov
Vehicle:
not specified
Details on test solutions:
Stock solutions (0.5 to 5.0 g/L) of the test chemicals were prepared in deionized water prior to inhibition testing. When necessary, the stock solutions were adjusted to pH 7.5±0.5 by the addition of 1N H2SO 4 or IN NaOH as required. 3,5-Dichlorophenol was included as a reference compound in each inhibition test. Stock solutions were prepared by dissolving 0.5 g of 3,5-dichlorophenol in 10 mL of IN NaOH and diluting to 30 mL with deionized water. The solution was adjusted to pH 7.5±0.5 by the addition of 8 mL of 1N H2SO 4, and then diluted to a total volume of 1 liter with deionized water.
Test organisms (species):
activated sludge
Details on inoculum:
Activated sludge was obtained from a local municipal wastewater treatment plant on the day prior to the first day of each series of inhibition tests. For a few of the latter studies, activated sludge was also obtained from a local industrial wastewater treatment plant. On return to the laboratory, the solids were allowed to settle and the waste liquor was discarded. The solids were then transferred into a 9-1iter laboratory-scale, semicontinuous activated sludge cylinder and diluted to approximately 8.5 liters 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 (dry weight) per liter. The system was then aerated continuously at a rate of 0.5 L/min and incubated at ambient temperature (21°C).
The system was supplemented daily with 50 mL of a synthetic sewage stock solution per liter of activated sludge. The synthetic sewage stock solution was composed of, per liter:
Bacto-Peptone, 16.0 g; Bacto-Beef extract, 11.0 g; urea, 3.0 g; K2HPO4 , 28.0 g; MgSO4.7H20, 0.2 g; CaCI2.2H20 , 0.4 g; and NaCl, 0.7 g. Final pH of the stock solution was adjusted to pH 7.0 with H3PO 4. The synthetic sewage stock solution was similar to that described by the OECD with the exception that the level of K2HPO4 was increased to 28.0 g for increased buffering capacity. Fresh stock solution was prepared as required and stored for not more than two days at 5°C.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
180 min
Post exposure observation period:
no
Hardness:
No data
Test temperature:
21 oC
pH:
7.5 ± 0.5
Nominal and measured concentrations:
Nominal
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Key result
Duration:
180 min
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 on result:
other: Confidence interval: 593-697
Results with reference substance (positive control):
The results obtained with the reference item 3,5-dichlorophenol, showed an EC50 12.4 mg/L (180 min). The EC50 was within the 2 to 25 mg/L range, and it was considered acceptable for the test

No data

Validity criteria fulfilled:
yes
Conclusions:
180 min EC50 > 1000 mg/L (respiration rate)
Executive summary:

The test item was tested according to OECD Guideline no 209: Activated Sludge, Respiration Inhibition Test. The study was conducted according to GLP.

Resulting EC50 >1000 mg/L (180 min).

Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Justification for type of information:
Read-across toxicity studies on one closely structural and physicochemical related substance: Benzoic acid.
For further read-across justification se document attached in section 13
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
inhibition of total respiration
Validity criteria fulfilled:
yes
Conclusions:
Based on a read-across to benzoic acid, the EC50(activated sludge, 3hr) is derived at >1000 mg/L
Executive summary:

Based on a read-across to benzoic acid, the EC50(activated sludge, 3hr) is derived at >1000 mg/L

Description of key information

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L

Additional information

Based on a read-across to benzoic acid, the EC50(activated sludge, 3hr) is derived at >1000 mg/L