Potassium phosphinate

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

Study period:

2009-07-27 till 2009-07-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: OECD guideline study in compliance to GLP standards.

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

yes

Remarks:

only one concentration was tested (limit test 1000 mg/L) Water solubility of the test substance is at least 5g/L

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

yes

Remarks:

in stead of a minimum of five concentrations, only one concentration was tested (limit test 1000 mg/L) Water solubility of the test substance is at least 5g/L

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Preparation of inoculum for exposure: The aerobic activated sludge from the wastewater treatment plant (ARA Ergolz II, Füllinsdorf / Switzerland) was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet to dry weight was calculated. Based on this ratio, an aliquot of washed sludge was suspended in tap water to obtain a concentration equivalent to 3 g dry material per liter.
- Pretreatment: Three days prior to use, the sludge was fed daily with 50 mL synthetic sewage feed per liter (composition is given in "other information on materials and methods") and was kept at room temperature under continuous aeration until use.
- Initial biomass concentration: 3.3 g/L dry weight
- pH of the activated sludge inoculum: 7.8

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

21°C

pH:

7.3 - 8.3

Dissolved oxygen:

8.1 - 9.4 mg 02/L

Nominal and measured concentrations:

Nominal concentration test substance: 1000 mg/L
Nominal concentration reference substance: 5, 16 and 50 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Material: 2000 mL glass beakers
- Aeration: continuously by intense stirring on magnetic stirrers to avoid possible foaming and/or stripping of the test item
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2
- Biomass loading rate: about 1.3 g dry material per liter test medium

TEST MEDIUM
- Preparation:
500.1 mg of the test substance was dissolved in 284 mL tap water by intense stirring for 5 minutes at room temperature. Afterwards 16 mL synthetic sewage feed and 200 mL activated sludge inoculum were added.
- Composition of test medium: as recommended in the guideline

EFFECT PARAMETERS MEASURED: oxygen consumption rate
- Methodology of measurement:
A well-mixed sample of each test medium was poured into a BOD-flask after incubation and was not further aerated. Then the dissolved oxygen concentration was measured and continuously recorded. During these measurements, the samples were continuously stirred on a magnetic stirrer. The oxygen consumption rate (in mg O2 L-1 minute-1) was determined from the linear part of the respiration curve in the range 6.5–2.5 mg O2/L. In case of very rapid oxygen consumption, the range used was below the limits indicated previously but always within the linear part of the respiration curve. In case of low oxygen consumption the rate was determined over a period of at least ten minutes.
- Measurement equipment: oxygen electrode (WTW TriOxmatic® 300) and an oxygen meter (WTW Oxi 539, Wissenschaftlich-Technische Werkstaetten WTW, Weilheim/Germany)

TEST CONCENTRATIONS
- Justification for using less concentrations than requested by guideline: based on EU testing guidelines A limit test was performed to demonstrate that the test item has no toxic effect on activated sludge up to the nominal test concentration of 1000 mg/L.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

>= 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Remarks on result:

other: no significant inhibitory effect

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

Remarks on result:

other: absence of toxic effect with limit test

Details on results:

The EC20, EC50 and EC80 (3 hours) could not be calculated but were clearly higher than 1000 mg/L

Results with reference substance (positive control):

- Results with reference substance are valid
- Relevant effect levels: EC50 (3h): 18 mg/L (95% confidence limits could not be calculated due to mathematical reasons)

Reported statistics and error estimates:

- Test substance: 3h EC20, EC50 and EC80 and their 95%-confidence limits could not be calculated because of the absence of a toxic effect
- Reference item: 3h EC50 was calculated by Probit Analysis

- Table 1: Detailed overview of the results obtained during the test as well as the influence of te test substance sodium hypophosphite and 3,the reference substance 5-Dichlorophenol on the oxygen consumption of activated sludge.

Vessel no.	Nominal concentration of test chemical (mg O2/L)	Oxygen consumption rate (mg O2L^-1min^-1)	Inhibition (%)	pH		Oxygen concentration (mg/L)
				start*	end*	start*	end*
Control A	0	1.505		7.6	8.3	8.6	8.5
Control B	0	1.333		7.7	8.2	8.5	8.8
Mean		1.419
Deviation (%)		11.5
Test item	1000	1.336	5.9	7.3	8.2	8.2	9.1
Reference item 1	5	1.553	-9.5	7.6	8.2	8.1	8.6
Reference item 2	16	0.770	45.7	7.6	8.3	8.6	8.8
Reference item 3	50	0.172	87.9	7.6	8.3	8.6	9.4

* Start and end of the 3h incubation period

- Controls: oxygen consumption rates of the two controls (run at the start and at the end of the test) differed by 12%.

Validity criteria fulfilled:

yes

Remarks:

see section overall remarks, attachments

Conclusions:

In the test conditions (limit test at 1000 mg/L) no toxic effects were observed. Thus the test substance has no significant inhibitory effect on the respiration rate of activated sludge.

Executive summary:

The authors tested the respiratory inhibition potential of sodium hypophosphite (CAS n° 10039-56-2) to activated sludge according to the EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test) and to the OECD guideline 209 (Activated Sludge, Respiration Inhibition Test). A 3h respiration inhibition limit test was performed with a nominal concentration of 1000 mg/L. In addition, two controls (at the start and end of the test) were tested in parallel with the test substance. Furthermore, in parellel 3,5-dichlorophenol (positive control) was tested at concentrations of 5, 16, and 50 mg/L.

Under these conditions no significant toxic effects were observed for the test substance and the results of the positive control confirmed suitability of the activated sludge and the method used. Hence, the EC10 (3h) of the test substance to activated sludge microorganisms was at least 1000 mg/L. The EC20, EC50, and EC80 (3h) could not be calculated but were clearly higher than 1000 mg/L.

Therefore, in the test conditions the test substance has no significant inhibitory effect on the respiration rate of activated sludge.

This study was performed according to OECD guidelines, in compliance to GLP standards (certificate included) and all validity criteria are fulfilled Hence the study can be consided as klimisch 1: reliable without restrictions.

Description of key information

Toxicity of sodium phosphinate to activated sludge microorganisms:
- EC10 (3h) >= 1000 mg/L (EU Method C.11 and OECD guideline 209)
- EC50 (3h) > 1000 mg/L (EU Method C.11 and OECD guideline 209)

By read-across, these results also apply to potassium phosphinate.

Additional information

A 3h respiration inhibition limit test was performed with a nominal concentration of 1000 mg/L of sodium phosphinate according to the EU Method C.11 and the OECD guideline 209 (Eisner, 2009).Two controls and a positive control (3,5 -dichlorophenol) were tested in parallel.

No significant toxic effects were observed and the results of the positive control confirmed suitability of the activated sludge and the method used. The EC10 (3h) of the test substance to activated sludge microorganisms was at least 1000 mg/L. The EC20, EC50, and EC80 (3h) could not be calculated but were clearly higher than 1000 mg/L. Therefore, sodium phosphinate has no significant inhibitory effect on the respiration rate of activated sludge and is thus not toxic to these microorganisms. By read-across, potassium phosphinate does not have any inhibitory effect either.