Potassium phosphinate

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

February 2010 till April 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Guideline study (OECD 106) in compliance with GLP regulation (only determination of the organic carbon content of the soils is not performed under GLP)

Qualifier:

according to guideline

Guideline:

OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Only determination of the organic carbon content of the soils is not performed under GLP

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Test temperature:

20 +/- 2 °C

Details on study design: HPLC method:

EQUIPMENT & CONDITIONS
- Pump: High pressure gradient system, consisting of two Shimadzu LC 10AD pumps and a Shimadzu SLC System Controller
- Autosampler: CTC PAL, UV 2000 (254 nm)
- Injector washing procedure:
wash solvent 1 - water/methanol/formic acid (80:20:0.5 v/v)
wash solvent 2 - water/acetonitrile/methanol (10:45:45 v/v)
wash sequence - 2 x syringe, 2 x injection port with each solvent
- Injection volume:2 µL
- Stationary phase: Hypersil SAX (Thermo); 2.1 mm x 100 mm particle size 5 µm
- Back pressure: approximately 70 bar at t=0
- Divert valve setting:
LC flow to MS: 0.2 min - 4.9 min (typical settings)
back-up flow: 100 µL/min or eluent A
- Detection system: negative mode, with m/z 65.0 as precursor ion and m/z 63.0 as product ion

MOBILE PHASES
Eluent A: water/methanol (80:20 v/v)
Eluent B: water/methanol (80:20 v/v) + 20 mM ammonium citrate

Analytical monitoring:

yes

Details on sampling:

- Sampling after 24h, 48h and 7 days

Details on matrix:

COLLECTION AND STORAGE
- Geographic location (See table 1 in other information on material and methods)
- Collection and handling procedures: according to ISO 10381-6 (Soil Quality-Sampling-Guidance on the collection, handling and storage of soil for the assessment of microbial processes in the laboratory)
- Sampling depth (cm): top 30 cm layer
- Soil preparation: 2 mm sieved, air dried at room temperature and homogenized. Disaggregation at minimal force to changed as little as possible the original texture. Soil samples were pre-equilibrated with about 90% of the targeted volume of the aqueous phase (0.01M CaCl2 solution) by shaking for at least 24 hours at 20 °C prior to application of the test item

PROPERTIES
See table 1 in other information on material and methods

Details on test conditions:

TEST CONDITIONS
- pH: 6.7
- other:
Soil-to-solution ratio: 1:1 (10g/10mL)
Concentration: 10 µg/mL

TEST SYSTEM
- Type, size and further details on reaction vessel: sealed Teflon centrifuge tubes
- Number of reaction vessels/concentration: 2

Computational methods:

- Adsorption and desorption coefficients (Kd): calculation with commercially available Excel computer program
- Freundlich adsorption/desorption isotherms: Due to the overall low adsorption of hypophosphite, Freundlich isotherms were not determined

Type:

Koc

Value:

15

Temp.:

20 °C

Remarks on result:

other: Soil II

Type:

Koc

Value:

11

Temp.:

20 °C

Remarks on result:

other: Soil III

Type:

Koc

Value:

11

Temp.:

20 °C

Remarks on result:

other: Soil IV

Type:

Koc

Value:

3.7

Temp.:

20 °C

Remarks on result:

other: Soil V

Type:

Kd

Value:

0.31

Temp.:

20 °C

Remarks on result:

other: Soil II

Type:

Kd

Value:

0.15

Temp.:

20 °C

Remarks on result:

other: Soil III

Type:

Kd

Value:

0.11

Temp.:

20 °C

Remarks on result:

other: Soil IV

Type:

Kd

Value:

0.16

Temp.:

20 °C

Remarks on result:

other: Soil V

Details on results (HPLC method):

- Average retention data for test substance: retention time 2.9 min

Recovery of test material:

95-110%

Concentration of test substance at end of adsorption equilibration period:

No consistent adsorption was seen for soil I

Concentration of test substance at end of desorption equilibration period:

The amount of hypophosphite desorbed could only be determined in soil II
In the other soils, the apparent amounts desorbed were zero, a quantification was not possible due to the high background concentrations in the residual water

Sample no.:

#2

Duration:

48 h

% Adsorption:

24

Sample no.:

#3

Duration:

48 h

% Adsorption:

13

Sample no.:

#4

Duration:

48 h

% Adsorption:

10

Sample no.:

#5

Duration:

48 h

% Adsorption:

14

Sample no.:

#2

Duration:

48 h

% Desorption:

<= 24

Transformation products:

not specified

Details on results (Batch equilibrium method):

PRELIMINARY TEST
- Initial test substance concentration:
Preliminary test 1: 1000 µg/L
Preliminary test 2: 100µg/mL and 10µg/mL
- Other:
Fixed equilibration time of 24 h

MAIN TEST: PERFORMANCE
- Experimental conditions maintained throughout the study: No, pH of 6.7 measured for aqueous phase before contact with the soils. After contact, pH ranged between 5.6 and 7.4

Preliminary test 1:

- Soils: I, III and V

- Soil-to-aqueous phase ratios: 1/2 (5 g/10 mL), 1/5 (5 g/25 mL) and 1/20 (1 g/20 mL)

- Recovery of hypophosphite in supernatants: close to 100% of applied material, no adsorption found

Preliminary test 2:

- Soils: all five soils

- Soil-to-solution ratio: 1:2

- With a soil-to solution ratio of 1:2 and a test concentration of 10 µg/mL the highest percentage bound was found, namely an adsorption of 4-15%.

Control:

Recovery: 96 ± 2.7%

Validity criteria fulfilled:

not applicable

Conclusions:

Under the experimental conditions, independent of the soil characteristics, sodium hypophosphite adsorption was low, with Kd and Koc values of 0.3 mL/g and 15 mL/g, respectively, as measured in soil II, or below. The adsorption was strongest in soil II, an acidic slit loam with a pH of 5.3. Desorption could only be measured in soil II, where 24% of the adsorbed amount could be recovered after 48 h of desorption. Thus, adsorption was at least partially reversible in this soil.

Executive summary:

The adsorption/desorption potential of sodium hypophosphite was assessed using five soils and the batch equilibrium method according to the OECD guideline 106. The study was conducted in compliance with the principles of Good Laboratory Practice regulations on the monohydrated form of the test item as the anhydrous form is highly hygroscopic and difficult to handle without specific precautions.

The following soils were used: Attenschwiller (soil I, silt loam), Bretagne 1 (soil II, silt loam); Mechtildshausen (soil III, loam), Speyer 2.3 (soil IV, sandy loam), and Tilbury (soil V, clay). These soils showed a range of texture and pH, characteristics important for adsorption of inorganic anions. After two preliminary tests, the adsorption/desorption kinetics of hypophosphite were determined in all five soils after 24h, 48h and seven days of agitation using a soil-to-solution ratio of 1:1 (10 g/10 mL) with a hypophosphite concentration of 10 µg/mL (100 µg applied).

No consistent adsorption was seen for soil I at any time, the recovery of hypophosphite in the supernatant was 95-110%. For the other soils, a plateau was reached after 24-48 h, with no further increase for the seven day time point. After 48 hours of agitation, adsorption represented 24%, 13%, 10% and 14% for soils II to V, respectively. The K_d values amounted to 0.31, 0.15, 0.11 and 0.16 mL/g for soils II to V, respectively, with corresponding K_oc values of 15, 11, 11 and 3.7 mL/g, respectively. Due to the overall low adsorption of hypophosphite, Freundlich isotherms were not determined.

Desorption was investigated after 168 h of adsorption. The amount of hypophosphite desorbed could only be determined in soil II, where up to 24% of the adsorbed amount could be recovered within 48 h. In the other soils, the apparent amounts desorbed were zero, a quantification was not possible due to the high background concentrations in the residual water.

Therefore, under the experimental conditions, independent of the soil characteristics, sodium hypophosphite adsorption was low, with K_dand K_ocvalues of 0.3 mL/g and 15 mL/g, respectively, as measured in soil II, or below. The adsorption was strongest in soil II, an acidic slit loam with a pH of 5.3. Desorption could only be measured in soil II, where 24% of the adsorbed amount could be recovered after 48 h of desorption. Thus, adsorption was at least partially reversible in this soil.

 

 

Description of key information

Results on sodium phosphinate were as follows:

- Koc value (20°C): max 15 L/kg (OECD guideline 106)
- Kd value (20°C): max 0.31 L/kg (OECD guideline 106)
- Desorption (20°C): 0 - 25% of the adsorbed amount within 48h (OECD guideline 106)

These results are considered to apply on potassium phosphinate by read-across.

Key value for chemical safety assessment

Koc at 20 °C:

15

Additional information

One study is reported for this endpoint. This study assessed the adsorption/desorption potential of sodium phosphinate using five soils and the batch equilibrium method according to the OECD guideline 106. For one out of five tested soils no consistent adsorption was seen, while for the other four soils adsorption represented 10 to 24%. For these soils the K_d values ranged between 0.11 and 0.31 L/kg, with corresponding K_oc values ranging from 3.7 to 15 L/kg. Desorption could only be determined in one soil, where up to 25% of the adsorbed amount could be recovered within 48 h. In the other soils, the apparent amounts desorbed were zero (quantification not possible due to the high background concentrations in the residual water).

[LogKoc: 1.18]