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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
The study was performed according to OECD guideline 209 and GLP but with a substance analogue and the data are read across.
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
not required
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: test substance was added to test vessel from a stock solution
- Controls: 3,5 dichlorophenol was used as positive control
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Preparation of inoculum for exposure: acitvated sludge suspension was washed 3 tines with tap water, and sieved with a 1mm mesh, adjusted to 7.5 g/L dry weight and pre-aerated overnight.
- Initial biomass concentration: An aliquot was added to the test vessels to obatin a sludge concentration of 1.5 g/L dry substance.
Limit test:
no
Total exposure duration:
180 min
Post exposure observation period:
duration of measurement of oxygen consumption: 8-10 minutes
Test temperature:
18-22 degrees Celsius
pH:
pH 7.1-7.2 before addition of inoculum
pH 7.5 - 7.9 after incubation time
Dissolved oxygen:
oxygen concentration during aeration >2.5 mg/L
oxygen concentration immediately before measurement > 6.5 mg/L
Salinity:
not applicable
Nominal and measured concentrations:
nominal concentrations of test substance: 1000, 500, 250, 125, 62.4 mg/L
nominal concentrations of reference substance: 1, 10, 100 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: Erlenmeyer vessel (nominal volume 250mL)
- test volume: 250 ml
- Aeration: by pressure air during incubation
- No. of vessels per concentration (replicates): 1
- No. of vessels per Blank control (replicates): 2
- Biomass loading rate: 1.5 g/L dry substance per vessel
- Synthetic medium: 8 mL per vessel 100-fold concentrated OECD medium

OTHER TEST CONDITIONS
- Adjustment of pH: not necessary

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- after incubation, the mixtures were placed in closed oxygen measuring cells. A chart recorder was used for measuring oxygen respiration rates.
- duration of measurement of oxygen consumption: 8- 10 minutes
Duration:
180 min
Dose descriptor:
EC10
Effect conc.:
180 mg/L
Nominal / measured:
nominal
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
180 min
Dose descriptor:
other: EC20
Effect conc.:
590 mg/L
Nominal / measured:
nominal
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
180 min
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
180 min
Dose descriptor:
other: EC80
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Reported statistics and error estimates:
Probit analysis according to Finney
Validity criteria fulfilled:
yes
Conclusions:
EC50 > 1000 mg/L

Description of key information

No reliable study with ammonium nitrate is present. Based  on a reliable OECD 209 guideline study, an EC50 against activated sludge > 1000 mg/L was derived for sodium nitrate. The NOEC was determined to be 180 mg/L. The read-across rationale can be found in the target study record.

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
180 mg/L

Additional information

No reliable study with ammonium nitrate is present. However, in a reliable OECD 209 guideline study, the respiration rate of the predominatly domestic sludge was determined after exposure to 62.4, 125, 250, 500, 1000 mg/L sodium nitrate for three hours. No significant inhibition of respiration rate of the sludge was recorded at this dose level. The substance was not toxic to waste water (activated sludge) bacteria at 1000 mg/l. Therefore, no further testing was needed. Hence, the EC50 of sodium nitrate exceeded 1000 mg/l (based on nominal concentrations), the NOEC was determined to be 180 mg/L.

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