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EC number: 211-402-2
CAS number: 643-79-8
A respiration inhibition test with
activated sludge according to OECD guideline 209 was carried out with
the test item o-phthalaldehyde. The test system was activated sludge
collected from a municipal sewage treatment plant, predominantly
receiving domestic sewage. The test was carried out under static
conditions with the nominal test item concentrations 1 / 3.1 / 9.8 / 31
/ 100 mg/L with and without allyl thiourea (ATU). The respiration rates
of the control, reference and test item replicates were measured after a
contact time of three hours, and the inhibitory effects of the test and
reference item were determined in comparison to the control respiration
rates. The coefficient of variation of the blank control respiration
rate (10 %) was lower than 30 %, while the respiration rate (43 mg/g/h)
was higher than 20 mg/g/h. The total (5.5 mg/L), heterotrophic (9.3
mg/L) and nitrification (1.8 mg/L) respiration values for the reference
item 3,5-dichlorophenol were between their respective ranges. All
validity criteria were met and therefore the data are considered valid.
The test substance o-phthalaldehyde
had a statistically significant effect on respiration observed during
the course of the study when compared to the blank control. ln the range
finding test there was significant inhibition at 100 mg/L and 1000 mg/L
from 71 to 99 % at all respiration values. From this test the definitive
rates were derived. As direct addition was utilised in the test media
preparations the total nominal values are used in the evaluation and no
further analytical evaluation was carried out. The determined EC50 value
of o-phthalaldehyde for total respiration was determined to be 76.6 mg/L
(95 % CI = 48.9–143.2 mg/L). For the endpoint organic carbon oxidation
(i.e. heterotrophic respiration) the EC50 was determined to be 33.0 mg/L
(95 % CI: 24.2–48.2 mg/L) and regarding ammonium oxidation (i.e.
nitrification) as 50 % was not reached, the EC50 value was determined to
be higher than the highest tested concentration of 100 mg/L, under these
test conditions. The respective no-observed effect concentration (NOEC)
values were 9.8 mg/L, 3.1 mg/L and 31.3 mg/L for total respiration,
heterotrophic respiration and nitrification; respectively.
Test organism: Activated sludge from
Test type: Static
Test item concentration in mg/L
ECX after 3 h of exposure
EC50 (95 % CI)
Reference item – 3,5-Dichlorophenol concentration (mg/L)
*The value of 50 % of nitriﬁcation respiration was not reached; therefore the EC50 is determined to be higher than the highest concentration tested.
Endpoint(s) effected: Total
respiration, organic carbon oxidation (heterotrophic), ammonium
In a 3-h activated sludge respiration
inhibition test according to OECD guideline 209 the toxicity of the test
item towards microorganisms was tested. All validity criteria were
fulfilled during testing. The determined ECx values are:
NOEC = 9.8 mg/L
EC50 = 76.6 mg/L (95 % CI: 48.9–143.2 mg/L)
NOEC = 3.1 mg/L
EC50 = 33.0 mg/L (95 % CI: 24.2–48.2 mg/L)
NOEC = 31.3 mg/L
EC50 > 100 mg/L
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