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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:
1988-11-30
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
It was used a settled sludge. The substance was not dissolved but distributed in the test medium. The sludge concentration in the test bottles was 2 g/L instead of 1.4 - 1.8 g/L.
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: stock solution: 20.8 rsp. 20.2 mg of the test substance were weighed and added to the test medium. The volume was adjusted to 200 mL with bidistilled water and aerated for 3 hours.
- Evidence of undissolved material (e.g. precipitate, surface film, etc):
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Preparation of inoculum for exposure: according to the method described in the guideline. Instead of a centrifuged sludge a settled sludge was used.
- Initial biomass concentration: 2.0 g/L
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Post exposure observation period:
none
Test temperature:
20 ± 2 °C
pH:
not determined
Nominal and measured concentrations:
104 and 101 mg/L (nominal)
Details on test conditions:
TEST SYSTEM
- Test vessel: BOD flasks with gas inlet
- Material, size, headspace, fill volume: 250 mL (size)
- Aeration: none during the test
- No. of vessels per concentration: 1
- No. of vessels per control: 1
- Biomass loading rate: 2 g/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated drinking water
16 g Peptone
11 g Meat extract
3.0 g Urea
0.7 g NaCl
0.4 g CaCl2 • 2 H2O
0.2 g MgSO4 • 7 H2O
2.8 g K2HPO4
per liter dechlorinated drinking water

OTHER TEST CONDITIONS
- Adjustment of pH: none

EFFECT PARAMETERS MEASURED: Oxygen consumption per hour in mg/liter

TEST CONCENTRATIONS
- Spacing factor for test concentrations: single dose in duplicate
- Justification for using less concentrations than requested by guideline: expected low toxicity of the test substance
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol at 32, 10, and 3.2 mg/L
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
Graphically determined
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: IC20
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
Graphically determined
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: IC80
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
Graphically determined
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
- Any observations that might cause a difference between measured and nominal values: none reported
- Effect concentrations exceeding solubility of substance in test medium: none reported
Results with reference substance (positive control):
- Results with reference substance valid: yes
- Relevant effect levels: IC50 12 mg/L, graphically determined

Description of key information

The inhibition of the degradation activity of activated sludge is not anticipated when tris(2,4-di-tert-butylphenyl)phosphite introduced in appropriate low concentrations.

Key value for chemical safety assessment

Additional information

The toxicity of tris(2,4-di-tert-butylphenyl)phosphite on microorganisms was tested in a limit test performed according to OECD guideline 209 [Ciba, 1988]. At the test concentration of about 100 mg/L no effect on the respiration rate of activated domestic sludge was measured.