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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:
1999
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
Qualifier:
according to guideline
Guideline:
ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Test substance: Tetrahydra-imidaza-(4,5-d)-imidazol-2,5-dion.
Batch number: Intermediate product from partie 692.
Date of manufacturing: 27 July 1998.
Purity: 97,6 % resp. 109,3 % based an elementary analysis of carbon and nitrogen respectively.
Impurities: 0.024% urea and 0.02% water.
Analytical monitoring:
yes
Details on sampling:
Not specified.
Vehicle:
yes
Remarks:
Synthetic medium 8mL/vessel 100-fold concentrated OECD Medium.
Details on test solutions:
The highest concentration tested for the test substance was 1000mg/L.
The highest concentration tested for the reference substance was 100mg/L.
Test organisms (species):
activated sludge
Details on inoculum:
The inoculum waws washed, brought to a concentration of 5g/L dry substance and aerated for 24 hours. 50mL were added to a total volume of 250mL to obtain a concentration of 1g/L dry susbtance in the test.
Test type:
not specified
Water media type:
not specified
Limit test:
no
Total exposure duration:
30 min
Remarks on exposure duration:
Exposure was carried out in Erlenmeyer-vessels.
Post exposure observation period:
Observation was carried out 30 minutes post exposure to the test substance.
Hardness:
Not specified.
Test temperature:
20 ± 2 °C.
pH:
6.7-7.2.
Dissolved oxygen:
Oxygen concentration during aeration: >2.5mg/L.
Oxygen concentration immediately before measurement: >6.5mg/L.
Duration of the measurement of oxygen consumption: 6-10mins.
Salinity:
Not specified.
Conductivity:
Not specified.
Nominal and measured concentrations:
The nominal concentration was the highest concentration tested; 1000mg/L.
Details on test conditions:
The EC20 is regarded as a limit value tor possible toxic effects in wastewater treatment plants. The test concentration in biodegradation tests should not exceed the EC20. The EC-values are based an added nominal concentrations and not an analytically determined values. The nominai concentrations which indicate a respiration inhibition of 20, 50 and 80 % can be taken from the graph of the inhibition curve.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Key result
Duration:
30 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: negative
Details on results:
No significant inhibition of respiration was measured up to the highest tested concentration of 1000mg/L.

  EC20 mg/L EC50 mg/L EC 80 mg/L Highest concentration tested
Test Substance - - - 1000
Reference substance ca. 2 ca. 21 ca. 77 100
Validity criteria fulfilled:
yes
Conclusions:
No significant inhibition of respiration was measured up to the highest tested concentration of 1000mg/L. It can therefore be concluded that the test substance showed no signs of toxicity to micro-organisms.
Executive summary:

This study aimed to determine the inhibition of oxygen consumption by aerobic micro-organisms (activated sludge) by the test substance in the activated sludge respiration inhibition test. This was conducted according to Annex of EEC Directive 88/302/EEC (November 1987), and corresponding to OECD guideline 209 (1993) and ISO standard 8192 (1986). The test results were reported as effective concentrations, indicating a respiration inhibition of 20,50, and 80% compared to a control assay without the test substance.

The results showed that no significant inhibition of respiration was measured up to the highest tested concentration of 1000mg/L. Based on the results it can be concluded that the test substance is non-toxic to micro-organisms under EC 1272/2008, within the experimental conditions of this study.

Description of key information

A study was performed to assess the inhibitory effect of the test substance on the oxygen consumption rate of aerobic micro-organims (activated sludge) after short term exposure (30 minutes). This was conducted according to; Annex of EEC Directive 88/302/EEC (November 1987), and corresponding to OECD Guideline 209 (1993) and ISO 8192 (1986). The test results were reported as effective concentrations, indicating a respiration inhibition of 20,50, and 80% compared to a control assay without the test substance.

EC50 = >1000 mg/L (nominal)

EC10 = >1000 mg/L (nominal)

NOEC = >1000 mg/L (nominal)

The results showed that no significant inhibition of respiration was measured up to the highest tested concentration of 1000mg/L. Therefore based on the test results, the test substance is non-toxic to micro-organisms under EC 1272/2008.

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information