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EC number: 208-419-2
CAS number: 527-60-6
EXPRESSION OF RESULTS
Calculate the oxygen consumption rate (R) in mg/l h according to
R = (Q1 -Q2)/ ∆t x 60
Q1= is the oxygen concentration at the beginning of the linear phase
Q2= is the oxygen concentration at the end of the linear phase (mg/l)
∆t= is the time interval between these two measurements (min)
The specific respiration rate (Rs) is expressed as the amount of oxygen
consumed per g dry weight of sludges per hour (mg/gh) according to the
SS= is the concentration of suspended solids in the mixture (g/l)
Different indices of R which may be combinated are:
T=total respiration rate
A=rate due to abiotic processes
B=rate based on blank assays control (mean)
To calculate the percentage inhibition It (%) of total consumption at
each concentration of the test item will be used the following equation:
It = [1 -(Rt-Rta)/Rtb]x100%
Rta is equal to 0 if there will be not oxygen uptake in the preliminary
test in the abiotic control or if the test item don't have strong
- the blank controls oxygen uptake rate should not be less than 20
mg oxygen per one gram of activated sludge (dry weight of suspended
solids) in an hour.
- the coefficient of variation of oxygen uptake rate in control
replicates should not be more than 30% at the end of definitive test.
- EC50 of 3,5 Dichlorophenol must be lie in the range 2 mg/l and
25 mg/l for total respiration.
INTERPRETATION OF RESULTS
EC50 values including their associated 95% confidence limit were
calculated by EPA PROBIT program version 1.5.
Quality criteria of the test were satisfied:
-the blank controls oxygen uptake rate: 30.28 mg oxygen per one gram of
activated sludge in an hour.
-the coefficient of variation of oxygen uptake rate in control
-EC50 of the reference substance 3,5 -Dichlorophenol: 14.3 mg/l for
-pH synthetic sewage feed: 7.57
-pH reference substance stock solution: 7.28
-oxygen consumption rate for abiotic control: 0,50 mg/l h
Mean percent inhibition total respiration rate of the test item 2,4,6
-trimethylphenol is detailed in the following table:
Mean percent inhibition total respiration rate of the reference
substance is detailed in the following table:
The absence of inhibition of oxygen consumption by the Test item, tested
in the range finding test, demonstrate that a definitive test is
The aim of this study is to determine the effects of the test item 2,4,6
trimethylphenol on microorganism from activated sludge by measuring
their respiration rate, accordin to OECD 209:2010.
The respiration rates of activated sludge both in control, reference and
treatment groups have been measured in an enclosed cell containing an
oxygen electrode after a contact time of 3 hours at 20°C.
The obtained results, in compliance with assay validity criteria,
interpreted in accordance to OECD 209:2010, show that the EC50 value of
the test item 2,4,6 trimethylphenol after 3 hours results higher than
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