Trimagnesium bis(orthophosphate)

Toxicity to microorganisms

Link to relevant study record(s)

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 justification attached to chapter 13

Reason / purpose for cross-reference:

read-across source

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 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.

Additional information

Experimental data on the toxicity of trimagnesium bis(orthophosphate) (CAS 7757-87-1) 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 trimagnesium bis(orthophosphate) to aquatic microorganisms are not expected.