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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:
other: GLP guideline study
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test item was added directly on a weight basis. The requisite mass to reach the desired concentrations was applied on pieces of Teflon, which were subsequently added to the dilution water. To achieve a maximum dilution of the test item, the assay was stirred for 24 h.
- Controls: 6 inoculum blank, 1 abiotic control
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Fresh samples of activated sludge are withdrawn from a sewage treatment plant (Ruhrverband Kläranlage, Schmallenberg, Germany) mainly fed with municipal wastewater.
- Pretreatment: On return to the laboratory the sludge was left alone to settle and the supernatant was decanted. The sludge was wahsed one time with isotonic solution. A small amount of the sludge was weighed and dried. From this result a stock solution of activated sludge in tap water was prepared with a mixed liquor suspended solids level of 3.8 g dry mass sludge/liter. The sludge stock solution was fed with synthetic sewage feed and was incubated aerated overnight at 20 ± 2°C in the dark. The amount of food applied was 50 mL/L. after this preincubation, the activated sludge was adjusted on a mixed liquor suspended solids level of 3.8 g dry mass sludge/litre.
- Initial biomass concentration: 1.5 g/L
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20°C
pH:
at test end: 8.2 - 8.4
Nominal and measured concentrations:
Nominal test substance concentrations: 10, 100, 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 1 L Erlenmeyer flasks
- Material, size, headspace, fill volume: glass, 500 mL total volume
- Aeration: aerated (air flow 0.5 - 1 L/min) during incubation
- No. of vessels per concentration (replicates): 1 for 10 and 100 mg/L; 3 for 1000 mg/L
- No. of vessels per control (replicates): 6

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Deionized water, free from inhibitory concentrations of toxic substances (e.g. Cu2+ ions) was used.
- Intervals of water quality measurement: At the end of the test, the pH of each vessel was recorded. Incubation temperature was measured at test start and at test end.

OTHER TEST CONDITIONS
- Adjustment of pH: Before start, the pH was checked and buffered to the pH of 7.5 ± 0.5 using NaOH (1N) solution.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable): The microbial respiration rate (total oxygen uptake including heterotrophic and nitrifcation uptake) was measured after 3 h.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
other: EC20
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, result is in the accepted range of 2 to 25 mg/L
- Relevant effect levels: EC50 (3h) = 11 mg/L

There is no significant inhibition of bacterial respiration by Boron orthophosphate up to and including a concentration of 1000 mg/L.

Inhibition (%) of the respiration rate by the test item

Test item concentration [mg T/L]

10 mg/L

100 mg/L

1000 mg/L

0.7%

-16.0%

6.6%

Validity criteria fulfilled:
yes
Conclusions:
There is no significant inhibition of bacterial respiration by Boron orthophosphate up to and including a concentration of 1000 mg/L. The EC50 is > 1000 mg/L.

Description of key information

Key value for chemical safety assessment

Additional information

The influence of Boron orthophosphate (CAS 13308-51-5) on the respiration of activated sewage sludge was investigated in a static OECD 209 test under GLP conditions. Activated sewage sludge was exposed to an aqueous dispersion of the test item at nominal concentrations of 10, 100 and 1000 mg/L for a period of 3 hours. The effect of Boron orthophosphate on the respiration of activated sewage sludge gave a 3h- EC50 of greater than 1000 mg/L. The EC20 (3h) was determined to be ≥ 1000 mg/L (nominal). No significant inhibition of bacterial respiration by Boron orthophosphate up to and including a concentration of 1000 mg/L was observed.