Phosphonic acid, monoethyl ester, sodium salt (1:1)

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:

25 Aug - 12 Sep 2014

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2000

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

no

Analytical monitoring:

yes

Matrix no.:

#1

Matrix type:

loam

% Org. carbon:

6.54

pH:

7.28

CEC:

28.87 other: cmol/kg

Matrix no.:

#2

Matrix type:

silt loam

% Org. carbon:

1.36

pH:

4.6

CEC:

11.53 other: cmol/kg

Matrix no.:

#3

Matrix type:

silty clay loam

% Org. carbon:

5.36

pH:

6.81

CEC:

22.9 other: cmol/kg

Matrix no.:

#4

Matrix type:

silt loam

% Org. carbon:

1.39

pH:

7.84

CEC:

7.08 other: cmol/kg

Matrix no.:

#5

Matrix type:

silt loam

% Org. carbon:

6.85

pH:

7.96

CEC:

22.13 other: cmol/kg

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: the soils selected for this study are from Jilin (#1, 125.73°, 42.28°), Jiangxi (#2, 117.07°, 28.23°), Jiangsu (#3, 120.30°, 31.60°), Shandong (#4, 116.06°, 34.81°), Gansu (#5, 100.40°, 38.90°), China
- Collection procedures: soil samples were transported using containers and under temperature conditions which guarantee that the initial soil properties were not significantly altered.
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): The soils were air-dried at ambient temperature (20°C ~ 25 °C). The soils were sieved to a particle size 0.3 mm. The moisture content of each soil was determined on three aliquots with heating at 105 °C until there is no significant change in weight.

PROPERTIES
- Particle composition 2-0.05 mm: 5.36 (#1), 15.0 (#2), 19.76 (#3), 39.04 (#4), 11.96 (#5)
- Particle composition 0.05 - 0.002 mm: 61.6 (#1), 42.76 (#2), 74.08 (#3), 38.8 (#4), 73.2 (#5)
- Particle composition < 0.002 mm: 33.04 (#1), 42.24 (#2), 6.16 (#3), 22.16 (#4), 14.84 (#5)
- Al (%): 5.72 (#1, 7.87 (#2), 7.01 (#3), 5.56 (#4), 6.42 (#5)
- Fe (%): 2.72 (#1, 3.99 (#2), 3.36 (#3), 2.52 (#4), 3.54 (#5)

Details on test conditions:

TEST SYSTEM
- Amount of soil and water per treatment (if simulation test): 2 g of soil and 50 mL of aqueous phase, concentration of the test substance in the solution (50.0 mg/L)
- Soil-water ratio (if simulation test): 1:25
- Blank: In every experiment one blank was run. It consisted of the soil and 0.01 mol/L CaCl2 solution, without test substance, and of weight and volume, respectively, identical to those of the experiment
- Number of reaction vessels/concentration: at least in duplicate
- Other: The standard stock solution I of the test substance (1.00 x 10^4 mg/L) was prepared by dissolving 1.0198 g test substance into 100 mL deionized water

Sample No.:

#1

Duration:

24 h

Sample No.:

#2

Duration:

24 h

Sample no.:

#1

Duration:

48 h

Sample no.:

#2

Duration:

48 h

Computational methods:

- Adsorption and desorption coefficients (Kd): The distribution coefficient Kd was the ratio between the content of the substance in the soil phase and the mass concentration of the substance in the aqueous solution, under the test conditions, when adsorption equilibrium was reached. Kd = C s(ads)eq/C aq(ads)eq = m s(ads)eq/m aq(ads)eq * V0/m soil (cm3 g^-1), where C s(ads)eq= content of the substance adsorbed on the soil at adsorption equilibrium (µg g^-1); C aq(ads)eq = mass concentration of the substance in the aqueous phase at adsorption equilibrium (µg cm^-3); this concentration is analytically determined taking into account the values given by the blanks. m s(ads)eq = mass of the test substance adsorbed on the soil at adsorption equilibrium (µg); m aq(ads)eq = mass of the test substance in the solution at adsorption equilibrium (µg); m soil = quantity of the soil phase, expressed in dry mass of soil (g); V0 = initial volume ofthe aqueous phase in contact with the soil (cm3).
The relation between Aeq and Kd is given by: Kd = Aeq/100-Aeq * Vo/m soil (cm3 g^-1), where Aeq = percentage of adsorption at adsorption equilibrium, %.
- Freundlich adsorption and desorption coefficients: The Freundlich adsorption isotherms equation related the amount of the test substance adsorbed to the concentration of the test substance in solution at equilibrium. The data were treated as under "Adsorption" and, for each test tube, the content of the test substance adsorbed on the soil after the adsorption test (C s(ads)eq), elsewhere denoted as x/m) was calculated. It was assumed that equilibrium had been attained and that C s(ads)eq represented the equilibrium value:
- Slope of Freundlich adsorption/desorption isotherms:
- Adsorption coefficient per organic carbon (Koc): The organic carbon normalized adsorption coefficient Koc relates the distribution coefficient Kd to the content of organic carbon of the soil sample. Koc = Kd * 100/%OC (cm3 g^-1), where %OC = percentage of organic carbon in the soil sample (g g^-1).
- Regression coefficient of Freundlich equation
- Other:

Sample No.:

#1

Type:

Koc

Value:

613.9 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#2

Type:

Koc

Value:

9 216 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#3

Type:

Koc

Value:

2 683 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#4

Type:

Koc

Value:

7 140 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#5

Type:

Koc

Value:

621 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#1

Type:

Kd

Value:

40.1 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#2

Type:

Kd

Value:

124.9 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#3

Type:

Kd

Value:

143.8 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#4

Type:

Kd

Value:

99.2 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Sample No.:

#5

Type:

Kd

Value:

42.5 L/kg

Remarks on result:

other: appropriate adsorption equilibrium time is 24 h

Adsorption and desorption constants:

The test substance adsorption isotherms on #1 and #2 soils are preferably followed Freundlich adsorption equation, correlative coefficients all are more than 0.9. The Freundlich adsorption coefficient ( Kf ads) values in five soils are 18.0, 397, 78.7, 9.79 and 69.5 µg^1-1/n * (cm3)^1/n g^-1 respectively. The 1/n value for different soils is 0.688 to 1.092. Desorption isotherms experiment was performed in the three soils (#1, #3, #4). The correlative coefficient of the Freundlich desorption isotherms equation was also more than 0.9 for three soils, therefore it is believed that the model can describe the desorption behaviors of the test substance in these soils as reported here after. The results of desorption isotherms show that the Freundlich desorption coefficient ( Kf des) values in the five soils are 51.3, 45.7, 100, 4.83 and 40.0 µg^1-1/n * (cm3)^1/n g^-1 respectively and the 1/n value ranged from 0.765 to 1.020.

Transformation products:

not measured

Details on results (Batch equilibrium method):

PRELIMINARY TEST
- Selection of optimal soil/solution ratios: two soil types (#1 and #2) and three soil/solution ratios described as follows were tested, 1.) 50 g soil and 50 mL aqueous solution of the test substance (ratio 1/1); 2.) 10 g soil and 50 mL aqueous solution of the test substance (ratio 1/5); and 3.) 2 g soil and 50 mL aqueous solution of the test substance (ratio 1/25). One control sample with only the test substance in 0.01 mol/L CaCl2 solution (no soil) was subjected to precisely the same steps as the test systems, in order to check the stability of the test substance in CaCl2 solution and its possible adsorption on the surfaces of the test vessels. A blank run per soil with the same amount of soil and total volume of 50 mL 0.01 mol/L CaCl2 solutions (without test substance) were subjected to the same test procedure. Air-dried soil samples were equilibrated by shaking with a minimum volume of 49.75 mL of 0.01 mol/L CaCl2 overnight (12 h) before the day of the experiment. Afterwards, 0.25 mL of the stock solution (1.00 x 10^4 mg/L) of the test substance was added. Samples were collected sequentially over a 24 h period of mixing (in the test at 2, 4, 6, 10, 24 h). After centrifugation and filtration, the aqueous phase of the first tube was recovered as completely as possible and was measured after 2 h, that of the second tube after 4 h, that of the third after 8 h, etc. The percentage adsorption Ati was calculated at each time point (ti) on the basis of the nominal initial concentration and the measured concentration at the sampling time (ti), corrected for the value of the blank. Plots of the Ati, versus time were generated in order to estimate the achievement of equilibrium plateau. The Kd value at equilibrium was also calculated. Based on this Kd value, appropriate soil/solution ratios were selected from OECD 106 Guideline, so that the percentage adsorption reached above 20% and preferably > 50%.

The adsorption coefficient (Kd) values of test substance in # 1, 2, 3, 4, 5 soil are 40.1, 124.9, 143.8, 99.2 and 42.5 cm3 g^-1, respectively. And the Koc values of test substance are 613.9, 9216, 2683, 7140 and 621.0 cm3 g^-1 in above soils respectively. The appropriate desorption equilibrium time is 48 h, and the desorption capacity of test substance in # 1, 2, 3, 4, 5 soil are 7.07%, 7.04%, 4.39%, 15.4% and 14.6% respectively. The desorption coefficient (Kdes) values of test substance in # 1, 2, 3, 4, 5 soil are 335.1, 336.8, 552.7, 137.9 and 149.1 cm3 g^-1, respectively.

The recoveries of the test substance from the whole test procedure were 95.8%, 91.0%, 88.1%, 97.4% and 95.9% under the test concentration 50.0 mg/L.

Table 1. Adsorption data of preliminary test

Time (h)	Ati(%)
	#1			#2
	Ratio 1/25	Ratio 1/5	Ratio 1/1	Ratio 1/25	Ratio 1/5	Ratio 1/1
2	32.5	55.2	94.1	62.9	100	100
4	37.4	68.4	96.5	65.2	100	100
6	42.9	71.3	98.2	72.7	100	100
10	54.6	84.5	100	80.5	100	100
24	61.1	93.2	100	83.0	100	100

 

Table 2. Results of Adsorption Kinetics

Time (h)	Ati(%)
	#1 (1/5)	#2 (1/1)	#3 (1/5)	#4 (1/1)	#5 (1/5)
2	32.5	62.9	73.5	50.4	42.6
4	37.4	65.2	75.8	53.9	45.4
6	42.9	72.7	76.4	56.2	56.7
10	54.6	80.5	79.5	67.5	59.4
24	61.1	83.0	85.0	79.8	62.5
Kd(cm^3/g)	40.1	124.9	143.8	99.2	42.5
Koc(cm^3/ g)	613.9	9216	2683	7140	621.0

 

Table 3. Results of desorption kinetics

Time (h)	Dti(%)
	#1	#2	#3
2	5.32	5.17	2.03
4	5.41	5.39	2.15
6	5.60	5.54	2.21
10	5.75	5.87	2.92
24	6.42	6.01	3.58
48	7.07	7.04	4.39
Kdes(cm^3/ g)	335.1	336.8	552.7

 

Table 4. Adsorption Isotherms data

C0(mg/L)	#1		#2		#3		#4		#5
	Cadss (eq)	Cadsaq (eq)	Cadss (eq)	Cadsaq (eq)	Cadss (eq)	Cadsaq (eq)	Cadss (eq)	Cadsaq (eq)	Cadss (eq)	Cadsaq (eq)
10.0	90.1	6.47	247	0.32	131	4.86	93.5	6.28	106	5.83
50.0	765	20.1	1057	8.58	1077	7.56	537	28.6	783	19.3
100	588	77.0	2145	15.9	1302	48.7	311	87.6	1737	31.9
500	5740	275	11324	56.1	7593	201	6737	232	3069	380
1000	10823	576	21844	144	11266	556	11909	526	5952	767

 

Table 5. Results of Adsorption Isotherms

Soil	Freundlich adsorption equation	KFads (µg^1-1/n(cm^3)^1/ng-1)	1/n
#1	y = 0.991x +1.256, r^2= 0.905	18.0	0.991
#2	y = 0.747x + 2.599, r^2= 0.932	397	0.747
#3	y = 0.808x + 1.896, r^2= 0.860	78.7	0.808
#4	y =1.092x + 0.991, r^2= 0.846	9.79	1.092
#5	y = 0.688x + 1.842, r^2= 0.836	69.5	0.688

 

Table 6. Desorption Isotherms data

C0(mg/L)	#1		#2		#3		#4		#5
	Cdess (eq)	Cdesaq (eq)	Cdess (eq)	Cdesaq (eq)	Cdess (eq)	Cdesaq (eq)	Cdess (eq)	Cdesaq (eq)	Cdess (eq)	Cdesaq (eq)
10.0	16.7	0.25	9.8	0.08	25.0	0.22	3.20	0.50	17.4	0.76
50.0	143	1.99	40.5	1.78	207	1.68	18.9	2.55	139	3.50
100	90.7	5.26	80.0	5.73	234	5.20	7.50	4.86	322	5.00
500	991.6	30.6	439	13.6	1453	12.9	236.4	32.9	418	38.5
1000	1985.1	35.2	855	18.5	2159	18.5	408	68.0	877	61.3

 

Table 7. Results of Desorption Isotherms

Soil	Freundlich desorption equation	KFdes (µg^1-1/n(cm^3)^1/ng-1)	1/n
#1	y = 0.891X + 1.710, r^2= 0.915	51.3	0.891
#2	y = 0.767x + 1.660, r^2= 0.875	45.7	0.767
#3	y = 0.967x+2.000, r^2= 0.943	100	0.967
#4	y= 1.020 x+0.684, r^2= 0.903	4.83	1.020
#5	y = 0.765x + 1.602, r^2= 0.845	40.0	0.765

Table 8. Results of Mass Balance

Soil	M0(µg)	Me(µg)	Mde(µg)	Ms(µg)	Recovery (%)
#1	2.50	1.00	0.0995	1.295	95.8
#2	2.50	0.429	0.0890	1.758	91.0
#3	2.50	0.378	0.0840	1.740	88.1
#4	2.50	1.43	0.128	0.877	97.4
#5	2.50	0.965	0.175	1.257	95.8

 

Validity criteria fulfilled:

not applicable

Description of key information

K_oc = 613.9 - 9216 L/kg (OECD 106)

log K_oc = 2.79 - 3.96 (OECD 106)

Additional information

One GLP study on the adsorption/desorption according to OECD guideline 106 is available for Fosetyl-sodium. In this study the adsorption/desorption of the test substance was investigated in five types of soil with different pH, texture, and organic carbon contents sampled from JiLin (#1, loam), Jiangxi (#2, silt loam), Jiangsu (#3, silty clay loam), Shandong (#4, silt loam) and Ganshu (#5, silt loam) provinces of China.

The results show that optimal soil/aqueous ratio for five soils were 1: 25, and the appropriate adsorption equilibrium time was 24 h. The adsorption coefficient (K_d) values of the test substance in #1, #2, #3, #4, #5 soil are 40.1, 124.9, 143.8, 99.2 and 42.5 L/kg, respectively. And the K_oc values of test substance are 613.9, 9216, 2683, 7140 and 621.0 L/kg in the soils, respectively. The appropriate desorption equilibrium time was 48 h, and the desorption capacity of test substance in #1, #2, #3, #4, #5 soil were 7.07%, 7.04%, 4.39%, 15.4% and 14.6%, respectively. The desorption coefficient (K_des) values of test substance in #1, #2, #3, #4, #5 soil were 335.1, 336.8, 552.7, 137.9 and 149.1 L/kg, respectively. The test substance adsorption isotherms on #1 and #2 soils are preferably followed Freundlich adsorption equation correlative coefficients all are > 0.9. The Freundlich adsorption coefficient (K_F^ads) values in five soils are 18.0, 397, 78.7, 9.79 and 69.5 µg^1-1/n (cm³)^1/n g^-1, respectively. The 1/n value for different soils is 0.688 to 1.092. Desorption isotherms experiment was performed in the three soils (#1, #3, #4). The correlative coefficient of the Freundlich desorption isotherms equation was also > 0.9 for three soils, therefore it is believed that the model can describe the desorption behaviours of the test substance in these soils as reported hereafter. The results of desorption isotherms showed that the Freundlich desorption coefficient (K_F^des) values in the five soils were 51.3, 45.7, 100, 4.83 and 40.0 µg^1-1/n (cm³)^1/n g^-1, respectively and the 1/n value ranged from 0.765 to 1.020.

Based on the measured log Koc values ranging from 2.79 - 3.96, the registered substance shows a moderate sorption to the soil/sediment compartment.