Phosphoric acid, mixed esters with biphenyl-4,4'-diol and phenol

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

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)

Analytical monitoring:

not required

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test substance is poorly soluble in water. At test initiation, weights of the test substance were added directly to the test bottles followed by RO (reverse osmosis) water (284 mL).

- Controls: activated sludge and synthetic sewage alone

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Preparation of inoculum for exposure: A sample of activated sludge was obtained the day before the start of the test. The mixed liquor suspended solids (MLSS) content was determined, synthetic sewage (50 mL/L) was added and the mixture was aerated overnight.
- Pretreatment: none
- Initial biomass concentration: ca. 4.0 g MLSS/L

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20-21 °C

pH:

test start: 7.3-7.5
test end: 7.9-8.1

Dissolved oxygen:

6.2-7.7 mg O2/L (initial DO concentration in the cultures)

Nominal and measured concentrations:

10, 30, 100, 300, 1000 mg/L (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: 500 mL bottles fitted with an oxygen probe, a sinter to deliver air and a nitrogen gas nozzle
- Aeration: oil-free compressed air at 1 L/min
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4
- Biomass loading rate: 1.6 g/L (MLSS)

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: reverse osmosis (RO) water
- In order to suppress foaming, a silicone based antifoam agent was added to each culture at an amount of 0.2 mL/L.

OTHER TEST CONDITIONS
- Adjustment of pH: no

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : oxygen concentration after 3 hours contact time

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

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:

respiration rate

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3 h): 16 mg/L (95% confidence limits could not be calculated)

Reported statistics and error estimates:

For calculation of the NOEC, Williams' test for a monotonic trend (preceeded by the F1 approximate test for monotonicity of dose-response at the 1% level) was used to compare the increasing dose levels of test compound with the control.
EC values (and 95% confidence intervals) and no observed effect concentration (NOEC) were calculated using SAFEstat programme SAS Proc NLIN (SAS Institute, 2002).

The test substance did not significantly inhibit the respiration rates of the samples of activated sludge at any of the concentrations employed. One replicate at 1000 mg/L had a maximum inhibition of 12%. The mean respiration rates of the sludge exposed to the test substance were higher at all tested levels than that of the control rate. Consequently the EC50 for inhibition could not be calculated but must be >1000 mg/L, the highest concentration tested in this study. 

Validity criteria fulfilled:

yes

Remarks:

The specific respiration rates in the controls were ≥20 mgO2/gh and the coefficient of variation was ≤30%. The EC50 of 3,5-dichlorophenol was in the accepted range of 2-25 mg/L.

Description of key information

Toxicity to microorganisms: not toxic to microorganisms: inhibition of respiration rates <15% at 1000 mg/L, NOEC > 1000 mg/L (OECD 209, EU C.11)

Additional information

The EC10 for the test material is much higher than its water solubility and thus a NOEC and PNEC cannot be determined.