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Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
see analogue justifiaction attached to chapter 13
Reason / purpose:
read-across source
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 directly added to the test medium and subsequently stirred for 24 hours.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Fresh samples of activated sludge were taken from a sewage treatment plant (Ruhrverband Kläranlage, Schmallenberg, Germany) mainly fed with municipal wastewater.
- Pretreatment: the sludge was washed with isotonic solution. A stock solution of activated sludge in tap water was prepared with a mixed liquor suspended solids level of 4.6 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.
- 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 ± 2 °C.
pH:
8.1 - 8.2
Nominal and measured concentrations:
Nominal test substance concentrations: 10, 100, 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: Erlenmeyer flask, 1 L
- Material, fill volume: glass, 500 mL
- Aeration: yes
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 6 + 1 abiotic control


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: deionized water, free from inhibitory concentrations of toxic substances (e.g. Cu2+ ions)


OTHER TEST CONDITIONS
- Adjustment of pH: yes, buffered to 7.5 ± 0.5 using H2SO4 (50 g/L) solution.


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Microbial respiration rate (total oxygen uptake including heterotrophic and nitrification uptake)

TEST CONCENTRATIONS
- Range finding study
- Test concentrations: 1000 mg/L
- Results used to determine the conditions for the definitive study: EC50 > 1000 mg/L
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
Details on results:
No inhibition of the respiration rate was observed
Results with reference substance (positive control):
EC50: 2 - 25 mg/L.

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

Test item concentration

10 mg/L

100 mg/L

1000 mg/L

Inhibition

-14.1 %

-4.4 %

0.5 %

Validity criteria fulfilled:
yes
Conclusions:
There is no significant inhibition of bacterial respiration by Calcium bis(dihydrogenorthophosphate) up to and including a concentration of 1000 mg/L. The EC50 of the test item is > 1000 mg/L.

Description of key information

Key value for chemical safety assessment

Additional information

Experimental data on the toxicity of magnesium hydrogen orthophosphate (CAS 7757-86-0) to aquatic microorganisms are not available. The assessment was therefore based on studies conducted with the analogue substance calcium bis(dihydrogenorthophosphate) (CAS 7758-23-8) as part of a read across approach, which is in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5.

The effect of calcium bis(dihydrogenorthophosphate) on the respiration of activated sludge was tested in a study following OECD guideline 209. Activated sludge was exposed to nominal substance concentrations of 10, 100 and 1000 mg/L respectively. The oxygen consumption of the activated sludge was observed for 3 hours. An effect on the respiration rate of the activated sludge was not observed. At test termination an EC10> 1000 mg/L (nominal) was determined. Based on the read across data toxic effects of magnesium hydrogen orthophosphate to aquatic microorganisms are not expected.