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EC number: 252-046-8
CAS number: 34455-29-3
Measurement Times and Specific Respiration Rates
Nominal conc. (mg/L)
Measurement time (minutes)
Specific respiration rate (Rs mg O2/gh)
Mean Rs (mg O2/gh)
Mean % inhibition
The data presented were calculated using unfounded values. Minor numerical differences may be observed in the respiration rate calculation if founded values are used to calculate the data. This minor discrepancy is not considered to be significant.
The Coefficient of variation for the control group was 16.3%.
study was to assess the effect of the test substance on the respiration
rate of activated sludge using the methods detailed in OECD Procedure
209 of the “Guidelines for Testing of Chemicals”: Activated Sludge,
Respiration Inhibition Test (carbon and ammonium oxidation), adopted 22
of activated sludge (suspended solids 1.6 g/L), fed with synthetic
sewage, were exposed to dilutions of the test substance for 3 hours.
Their rates of oxygen consumption were determined using oxygen
electrodes and were compared with those of two replicate controls that
contained activated sludge and synthetic sewage alone. The nominal the
test substance concentrations used in the study were 10, 100 and 1000
mg/L; a single replicate was tested at 10 mg/L and 100 mg/L and three
replicates at 1000 mg/L. The control consisted of two replicates. Single
replicates of the reference inhibitor 3,5-dichlorophenol (3,5-DCP) were
tested at 3, 10 and 32 mg/L, as a positive control.
mean specific respiration rate (Rs) of the control cultures incubated
alongside the test mixtures was 20 mg O2/gh with a coefficient of
variation (CV) of 16.3%. Sludge respiration rates were progressively
reduced in the presence of increasing concentrations of 3,5-DCP, with
24%, 50% and 81% inhibition obtained at 3, 10 and 32 mg/L respectively.
The EC50 of 3,5-DCP was approximately 10 mg/L and as such was
within the acceptable range of 2 to 25 mg/L. These results demonstrated
that the sample of activated sludge employed was sensitive to inhibition
and that the test was valid.
were insufficient replicates containing test substance for a credible
statistical analysis to be performed, however at the end of the
incubation period, levels of inhibition were 9%, 7% and 22% (mean) at
nominal test concentrations of 10, 100 and 1000 mg/L respectively, the
latter being considered significant. Therefore the test substance
notably inhibited the respiration rates of the samples of activated
sludge at a nominal concentration of 1000 mg/L. Based on these results
it can be assumed that the NOEC lies between 100 and 1000 mg/L and the EC50 can
be considered to be greater than the highest level tested, 1000 mg/L.
3-hour EC50 >1000 mg/L
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