Phosphinic acid

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Reference 1

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: Guideline study according to guidelines OECD n° 209 and EU Method C.11 following GLP standards

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

The inoculum was handled as described in the guidelines (e.g. pretreatment, preparation etc.)

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Hardness:

No data

Test temperature:

19°C - 20°C

pH:

7.4 - 8.4

Dissolved oxygen:

7.9 - 9.0 mg O2/L

Nominal and measured concentrations:

Nominal test substance concentration: 1565 mg/L (equivalent to 1000 mg pure hypophosphorous acid per liter)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Material, size, headspace, fill volume: 2000-mL glass beakers
- Aeration: continuously aerated by intense stirring on magnetic stirrers
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2
- Sludge concentration: 2.7 g/L dry weight (corresponding to ~1.1 g dry material per liter test medium)


TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: tap water


OTHER TEST CONDITIONS
- Adjustment of pH: yes
pH of the activated sludge inoculum was adjusted from 8.8 to 7.1 with a diluted sulfuric acid solution
pH of the stock solution of the test substance was adjusted from pH 1.1 to 7.4 with about 15 mL of a 1M sodium hydroxide solution


EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Oxygen concentration at the start and end of the 3-hour incubation period


TEST CONCENTRATIONS
- Justification for using less concentrations than requested by guideline: limit test

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

>= 1 565 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.:

> 1 565 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

The test substance phosphinic acid had no significant inhibitory effect (≤15%) on the respiration rate of activated sludge after the 3h incubation period at the limit test concentration of 1565 mg/L (equivalent to 1000 mg pure phosphinic acid/L).

Results with reference substance (positive control):

- Results with reference substance are valid
- Relevant effect levels:
EC50 (3h) of the reference item 3,5-dichlorophenol: 14 mg/L (which is within the guideline-recommended range of 2-25 mg/L.)

Reported statistics and error estimates:

The 3h EC20, EC50 and EC80 values of the test substance phosphinic acid and their 95%-confidence limits could not be calculated because of the absence of a toxic effect. However, probit analysis was used for the results obtained for the reference substance.

- Oxygen consumption rates of the two controls differed by 3% (guideline recommendations: the two control respiration rates should be within 15% each other)

Table 1: Influence of phosphinic acid (Test Item) and 3.5 Dicholorophenol (Reference item) on the Oxygen consumption of Activated Sludge.

Vessel n°	Nominal concentration of test chemical (mg/L)	Oxygen consumption rate (mg O2 L-1 min-1)	Inhibition (%)	pH values		Oxygen concentration (mg O2/L)
Control
AB	00	1.0961.131		start 7.6 7.9	end8.4 8.4	start8.1 7.9	end8.38.9
Mean deviation (%)		1.114 3.2
Test Item
10	1565	1.096	1.6	7.8	8.3	8.0	8.7
Reference Item
1 23	51650	1.0910.4260.120	2.061.789.2	7.6 7.4 7.6	8.38.48.3	8.58.68.5	8.89.09.0

 

Validity criteria fulfilled:

yes

Remarks:

see overall remarks

Conclusions:

The authors tested the inhibitory effect of phosphinic acid on the respiration rate of aerobic wastewater microorganisms of activated sludge according to the OECD guideline n° 209 (Activated Sludge, Respiration Inhibition Test) and EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test). Under these test conditions phosphinic acid had no inhibitory effect on the respiration rate of activated sludge at a concentration of 1565 mg/L (equivalent to 1000 mg pure phosphinic acid per liter) after 3h of exposure (limit test).

Executive summary:

The authors tested the inhibitory effect of phosphinic acid (CAS n° 6303 -21 -5) on the respiration rate of aerobic wastewater microorganisms of activated sludge in a 3-hour respiration inhibition test according to the OECD Guideline for Testing of Chemicals, n° 209 (Activated Sludge, Respiration Inhibition Test) and the EU Commission Directive 88/302/EEC, Part C.11, Commission Regulation (EC) No. 440/2008, Part C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test). A limit test with a nominal test concentration of 1565 mg/L (equivalent to 1000 mg pure phosphinic acid per liter) was performed. In parallel two controls and three different concentrations of the reference substance 3,5-dichlorophenol (5, 16, and 50 mg/L) were tested. The results of these treatments confirmed suitability of the activated sludge and the method used. Under these test conditions phosphinic acid had no inhibitory effect on the respiration rate of activated sludge at a concentration of 1565 mg/L (equivalent to 1000 mg pure phosphinic acid per liter) after 3h of incubation (pH adjusted). Thus, the 3h NOEC (EC10) of phosphinic to activated sludge microorganisms was at least 1565 mg/L (equivalent to 1000 mg pure phosphinic acid per liter) after pH adjustment. This value might be higher but such concentrations were not tested. The 3h EC20, EC50, and EC80 could not be calculated but should clearly be higher than 1565 mg/L (equivalent to 1000 mg pure phosphinic acid per liter) after pH adjustment.

This study was performed following GLP standards (certificate included) and validity criteria were fulfilled. Hence this study is considered Reliable without restriction as it is a guideline study following GLP standards (Klimisch 1)

Reference 2

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

2009-07-27 till 2009-07-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

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 phosphinate 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:

The result of the toxicity to aquatic algae of the sodium phosphinate was used to determine the toxicity of phosphinic acid as it is commercially prepared as the result of pH adjustment of the sodium phosphinate (salt).
Therefore conclusions are the same:
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 data from sodium phosphinate are used to determine the respiratory inhibition potential of phosphinic acid as it is commercially prepared as the result of pH adjustment of the Sodium phosphinate salt. Therefore conclusions are the same.

The authors tested the respiratory inhibition potential of sodium phosphinate (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 sodium phosphinate has no significant inhibitory effect on the respiration rate of activated sludge. By read across approach, phosphinic acid is also assumed to have no significant inhibitory effect on 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

One key study is available on phosphinic acid and was performed according to standard guideline and GLP compliant.
Phosphinic acid had no inhibitory effect on the respiration rate of activated sludge at a concentration of 1565 mg/L (=1000 mg/L as pure substance) after 3h of incubation thus, the 3h NOEC (EC10) of phosphinic to activated sludge microorganisms was at least 1565 mg/L. 

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1 000 mg/L

Additional information

One key study on phosphinic acid and one supportive study on sodium phosphinate are available.

The key study tested the inhibitory effect of phosphinic acid on the respiration rate of aerobic wastewater microorganisms of activated sludge in a 3-hour respiration inhibition test according to the OECD 209 Guideline. A limit test with a nominal test concentration of 1565 mg/L (equivalent to 1000 mg/L as pure phosphinic acid) was performed. In parallel two controls and three different concentrations of the reference substance 3,5-dichlorophenol (5, 16, and 50 mg/L) were tested. Under these test conditions phosphinic acid had no inhibitory effect on the respiration rate of activated sludge.

The 3h EC50 and NOEC of phosphinic acid to activated sludge microorganisms was > 1565 mg/L and equal or above 1565 mg/L respectively after pH adjustment This study was performed following GLP standards (certificate included) and validity criteria were fulfilled.

One supportive study on sodium phosphinate is available.

Phosphinic acid is commercially prepared as the result of pH adjustment of the sodium phosphinate salt. The main assumption is that in aqueous solution the acid and the salt will be fully dissociated and the sodium cation is not significant in respect to toxicity on aquatic microorganisms which are expected to be related to the phosphinate anion. Hence the phosphinic acid properties can be directly read across from its salt, the sodium phosphinate.

The authors tested the respiratory inhibition potential of sodium phosphinate 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 parallel 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. This study was performed according to OECD guidelines, in compliance to GLP standards (certificate included) and all validity criteria are fulfilled

The result on sodium phosphinate are similar to those obtain on the phosphinic acid reinforcing the read across approach between these two substances for aquatic organisms.