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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:
04 December 2007
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
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Molecular weight: 553.05
CAS Number: 15792-20-8
Description: Red powder
Batch: 070711
Purity: >96.4%
Test substance storage: At room temperature in the dark
Stability under storage conditions: Stable
Expiry date: 11 July 2011
Analytical monitoring:
no
Details on sampling:
Not applicable
Vehicle:
yes
Remarks:
Milli-RO water
Details on test solutions:
The batch of R507-2 was a red powder with a purity of at least 96.4%.

Under the conditions of the present test R507-2 was hardly soluble in water. Therefore, the test concentrations were prepared separately in Milli-RO water (tap water purified by reverse osmosis; Millipore Corp., Bedford, Mass., USA). Initial loading rates of 200 mg/I were stirred for 24 hours in the test bottles. Subsequently, synthetic sewage feed and sludge were added (see section 6.4) resulting in a loading rate of 100 mg/I. This loading rate was tested in duplicate. Optimal contact between the test substance and test medium was ensured applying continuous aeration and stirring.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Activated sludge obtained from a municipal sewage treatment plant: 'Waterschap de Maaskant', 's-Hertogenbosch, the Netherlands, receiving predominantly domestic sewage.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Post exposure observation period:
Not applicable
Hardness:
Not mentioned in study report
Test temperature:
18.1 to 18.5°C
pH:
8.2
Dissolved oxygen:
8.5-9.5 mg/L
Salinity:
Not applicable, as freshwater study
Nominal and measured concentrations:
100 mg/L loading rate
Details on test conditions:
Vessels: All glass, approximately 300 ml oxygen bottles and 1 litre test bottles.

Air supply: Clean, oil-free air

Performance of the test: Following the 24 hours of stirring, the synthetic sewage feed (16 ml) and the activated sludge
(200 ml) were added to the test substance mixture. Milli-RO water was added to provide a final volume of 500 ml with a final test substance loading of 100 mg/I. The mixture was aerated during the contact time, using a pipette as an aeration device.

After the 3-hour contact time, a well mixed sample of the contents was poured into a 300 ml oxygen bottle, and the flask was sealed with an oxygen electrode connected to a recorder, forcing the air out of the vessel. Oxygen consumption was measured and recorded for approximately 10 minutes. During measurement, the sample was not aerated but continuously stirred on a magnetic stirrer.
The pH and temperature were determined in the remaining part of the reaction mixture.

This procedure was repeated for the duplicate concentration. Two controls without test substance were tested in each test series, one at the start and one at the end.
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Details on results:
No inhibition of respiration rate of the sludge was recorded at 100 mg R507-2 per litre. The duplicate measurement confirmed the result of the first measurement (values of -1 and 5% inhibition only were recorded). Therefore, no further testing was needed.
Hence, the EC50 of R507-2 exceeded 100 mg/I (based on nominal concentrations).
Results with reference substance (positive control):
5 mg/L: 30% inhibition
12 mg/L: 65% inhibition
30 mg/L: 84% inhibition

Controls (C) and R507-2 (T): pH, oxygen concentration, oxygen consumption and percentage inhibition of the respiration rate

 

Flask

Loading rate (mg/I)

Oxygen cone. at the start (mg 02/l)

Oxygen consumption (mg 02/1/h)

% Inhibition respiration rate

pH

T1

100

9.0

50

-1*

8.2

T2

100

9.2

47

5

8.2

*A negative value indicates stimulation of the respiration rate of the sludge. This value is considered as not significant.

 

Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of this present test, R507-2 was not toxic to waste water (activated sludge) bacteria at a nominal concentration of 100 mg/I. Thus, the EC50 of R507-2 exceeded 100 mg/I (based on nominal concentrations).

Description of key information

Under the conditions of this present test, R507-2 was not toxic to waste water (activated sludge) bacteria at a nominal concentration of 100 mg/I.

Thus, the EC50 of R507-2 exceeded 100 mg/l (based on nominal concentrations).

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L

Additional information