Boron orthophosphate

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:

other: GLP guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

GLP compliance:

yes (incl. QA statement)

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Fresh samples of activated sludge are withdrawn from a sewage treatment plant (Ruhrverband Kläranlage, Schmallenberg, Germany) mainly fed with municipal wastewater.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.

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.