Pirimiphos-methyl

Adsorption / desorption

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

adsorption / desorption, other

Remarks:

batch equilibrium method

Type of information:

experimental study

Adequacy of study:

key study

Study period:

08 Dec 1992 to 21 Dec 1992

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

not specified

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 ± 2

Analytical monitoring:

yes

Details on sampling:

All aqueous phases of the soil:water slurries were analysed for radiochemical content after the 24 hour adsorption and after 24 hours desorption.

Matrix no.:

#1

Matrix type:

loamy sand

% Clay:

11

% Silt:

5

% Sand:

84

% Org. carbon:

1.57

pH:

7.9

CEC:

9.4 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

loamy sand

% Clay:

11

% Silt:

7

% Sand:

82

% Org. carbon:

1.68

pH:

7.8

CEC:

6.5 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

loamy sand

% Clay:

12

% Silt:

6

% Sand:

82

% Org. carbon:

2.96

pH:

7.9

CEC:

13.6 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

sand

% Clay:

4

% Silt:

5

% Sand:

91

% Org. carbon:

0.29

pH:

5.5

CEC:

1.4 meq/100 g soil d.w.

Matrix no.:

#5

Matrix type:

silty clay loam

% Clay:

28

% Silt:

54

% Sand:

18

% Org. carbon:

1.63

pH:

4.9

CEC:

17.6 meq/100 g soil d.w.

Matrix no.:

#6

Matrix type:

sandy loam

% Clay:

18

% Silt:

22

% Sand:

60

% Org. carbon:

1.92

pH:

4.7

CEC:

10.8 meq/100 g soil d.w.

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: See Table 1 in 'Any other information on materials and methods incl. tables'
- Soil preparation: The soils were dried, then passed through a sieve (2mm mesh). Soils were irradiated (gamma) prior to use, in order to minimise degradation of the test substance during the study period. Approximately 500g of each soil was irradiated. The dose received was at least 25 KGys, which is sufficient to eliminate any living organisms within the soil.
- Storage: The Irradiated soil was stored In double wrapped polythene bags at 5 ± 4°C prior to use.

PROPERTIES
- Moisture content: The moisture contents of the air dried sells were determined by oven-drying a sample (approximately 20 g) of each soil at 107°C overnight.
- Properties: See Table 2 in 'Any other information on materials and methods incl. tables'

Details on test conditions:

TEST SYSTEM
- Preparation of soil Slurries see Table 3 in 'Any other information on materials and methods incl. tables'
- Soil solution ratio: 1g : 20 cm3 aqueous phase
- Number of reaction vessels/concentration: 2
- Test performed in closed vessels: The adsorption and desorption studies were carried out with amounts of alr dried soils equivalent to 1 g (oven dried weight) weighed directly into 50cm3 glass centrifuge tubes with self-seating stoppers. Prior to 14C-labelled test substance treatment, each soil sample was equllibrated overnight In 0.01M aqueous CaCl2 (approximately 19cm3) with continuous mixing on an endoverend shaker at approximately 1,300 revolutions per hour (rph) at 20 ± 2°C. All aqueous CaCl2 solutions used in this study were sterilised by autoclaving prior to use. The use of 0.01 M CaCl2 solution prevented dispersion of the clay colloids and simulated the salt concentration normally found In soils. Samples were also generated as treatment controls (containing no soil) to determine if the chemical adsorbed to the glass, and soil blanks (containing only soil and aqueous CaCl2 solution) to be used for background determinations in liquid scintillation counting (LSC).
- Method of preparation of test solution: Treatment solutions were prepared separately In volumetric flasks (25 cm3). The appropriate volumes of radlotabelled and unlabelled chemical stock solutions were added to the flasks such that when aliquots (1 cm3) of the prepared treatment solutions were added to the soil:water slurries the required concentration of the test substance in the aqueous phase would be achieved. All flasks were made up to volume with sterile aqueous CaCl2 solution (0.01 M) and each assessed by LSC to determine the actual concentrations of 14C-labelled test substance achieved. Methanol (2 - 4 cm3) was added to the treatment solution prior to making up to volume In order to ensure that the test substance remained In solution. However, It was considered that the addition of this amount of organic solvent would not affect the eventual equilibrium In the sotl:water slurries, because It would be less than 1 percent of the total volume In the aqueous phase. The soils were split into two sets of three and the equllibrations carried out on two separate occasions under the same conditions. A fresh treatment solution was prepared for each set of equilibrations.

- Equilibration of soil slurries(Adsorption stage): Duplicate soil slurries (for each treatment rate), pre.equilibrated with aqueous 0.01 M CaCl2 solution (approximately 19cm3) in glass centrifuge tubes (50cm3) were fortified with the test substance. Each fortification was in 1 cm3 0.01M CaCl2 solution, sufficient to achieve Initial aqueous phase solution concentrations of 0.04, 0.1, 0.2, 1.0 and 2.0 μg/cm3. The tubes containing the soil slurries were transferred to an end-over-end shaker and continuously mixed at approximately 1,300 revolutions per hour (rph) for 24 hours, at 20 ± 2°C.

- Equilibration of soil slurries(Desorption stage): Replicate pairs of tubes of all treatment rates were prepared, equilibrated, treated, reequilibrated and centrifuged as described in the adsorption stage. The tubes were then used for the single step desorption stage.

PRELIMINART STUDY
The preliminary "time of adsorption experiment" showed that the distribution of 14C-labelled test substance between the soil and the aqueous phase had appeared to reach equilibrium within 6 hours. In the definitive experiment a 24 hour equlllbratlon time for both the adsorption and desorption phases was used.

Duration:

24 h

Temp.:

20 °C

Remarks:

Nominally applied rates were 0.04, 0.1, 0.2, 1.0 and 2.0 μg/cm3

Duration:

24 h

Temp.:

20 °C

Key result

Sample No.:

#1

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

950 L/kg

pH:

7.9

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

1.57

Key result

Sample No.:

#2

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

1 500 L/kg

pH:

7.8

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

1.67

Key result

Sample No.:

#3

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

1 100 L/kg

pH:

7.9

Temp.:

20 °C

Matrix:

Loamy sand

% Org. carbon:

2.96

Key result

Sample No.:

#4

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

4 100 L/kg

pH:

5.5

Temp.:

20 °C

Matrix:

Sand

% Org. carbon:

0.29

Key result

Sample No.:

#5

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

8 500 L/kg

pH:

4.9

Temp.:

20 °C

Matrix:

Silty clay loam

% Org. carbon:

1.63

Key result

Sample No.:

#6

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

2 100 L/kg

pH:

4.7

Temp.:

20 °C

Matrix:

Sandy loam

% Org. carbon:

1.92

Sample No.:

#1

Phase system:

solids-water in soil

Type:

other: Koc- Desorption Freundlich Coefficients

Value:

1 300 L/kg

Temp.:

20 °C

pH:

7.9

Matrix:

Loamy sand

% Org. carbon:

1.57

Sample No.:

#2

Phase system:

solids-water in soil

Type:

other: Koc- Desorption Freundlich Coefficients

Value:

2 300 L/kg

Temp.:

20 °C

pH:

7.8

Matrix:

Loamy sand

% Org. carbon:

1.67

Sample No.:

#3

Phase system:

solids-water in soil

Type:

other: Koc- Desorption Freundlich Coefficients

Value:

1 500 L/kg

Temp.:

20 °C

pH:

7.9

Matrix:

Loamy sand

% Org. carbon:

2.96

Sample No.:

#4

Phase system:

solids-water in soil

Type:

other: Koc- Desorption Freundlich Coefficients

Value:

5 000 L/kg

Temp.:

20 °C

pH:

5.5

Matrix:

Sand

% Org. carbon:

0.29

Sample No.:

#5

Phase system:

solids-water in soil

Type:

other: Koc- Desorption Freundlich Coefficients

Value:

8 800 L/kg

Temp.:

20 °C

pH:

4.9

Matrix:

Silty clay loam

% Org. carbon:

1.63

Sample No.:

#6

Phase system:

solids-water in soil

Type:

other: Koc- Desorption Freundlich Coefficients

Value:

2 600 L/kg

Temp.:

20 °C

pH:

4.7

Matrix:

Sandy loam

% Org. carbon:

1.92

Adsorption and desorption constants:

See Table 11 - Table 14 in 'Any other information on results incl. tables'.

Recovery of test material:

Table 4 - Table 8 in 'Any other information on results incl. tables'.
- Recovery of Radioactivity: Recoveries of radioactivity from the samples assessed averaged 93% of that nominally applied and were generally greater than 90%. These recoveries therefore show a good relationship between radiolabeled material applied and that recovered.

Concentration of test substance at end of adsorption equilibration period:

See Table 9 in 'Any other information on results incl. tables'.

Concentration of test substance at end of desorption equilibration period:

See Table 10 in 'Any other information on results incl. tables'.

Sample no.:

#1

Duration:

24 h

% Adsorption:

49

Sample no.:

#2

Duration:

24 h

% Adsorption:

58

Sample no.:

#3

Duration:

24 h

% Adsorption:

65

Sample no.:

#4

Duration:

24 h

% Adsorption:

32

Sample no.:

#5

Duration:

24 h

% Adsorption:

86

Sample no.:

#6

Duration:

24 h

% Adsorption:

61

Sample no.:

#1

Duration:

24 h

% Desorption:

37

Sample no.:

#2

Duration:

24 h

% Desorption:

32

Sample no.:

#3

Duration:

24 h

% Desorption:

27

Sample no.:

#4

Duration:

24 h

% Desorption:

39

Sample no.:

#5

Duration:

24 h

% Desorption:

13

Sample no.:

#6

Duration:

24 h

% Desorption:

33

Transformation products:

not measured

Details on results (Batch equilibrium method):

An overview of the results is provided in Table 4 - Table 14 in 'Any other information on results incl. tables'.

- Stability of 14C-labelled test substance in the Test System: TLC analysis of the aqueous and soil extracts derived from the soil : water slurries from the high pH soils, after both the adsorption and desorption steps, demonstrated that there had been little or no degradation of the 14C-labeleld test substance. There was always greater than 90% of extracts identified as parent material. These data demonstrate that the chemical was stable during the equilibration process in these soils. Thus all calculations of adsorption and desorption coefficients, for the high pH soils assumed that all 14C-material In the aqueous or soil phases was the test substance.
TLC analysis of the lower pH soils demonstrated the occurrence of large amounts of degradation products In the aqueous phase of the slurries (> 30% of the aqueous extracts), these data showing that the chemical was unstable during the equilibration process In these soils. Thus, in the calculation of adsorption and desorption coefficients concentrations in the aqueous phase were adjusted for the amount of degradation observed in this phase of the soil : water slurries. However, TLC analysis of the soil extracts derived from the same soils showed little or no degradation, with always greater than 90% of these extracts being identified as parent test substance. Therefore, no adjustment was made to concentrations to 14C-labelled test substance concentrations derived from LSC determinations in order to calculate the amount of chemical adsorbed to soil. No attempt was made to identify the products formed.

- Adsorption of 14C-labelled test substance to Soil:
The test substance was shown to be strongly adsorbed to soil. Average Kd values in the six soils ranged from 15 in the sand soil ('Lilly Field') to 180 in silty clay loam soil ('Nebo'). Freundllch adsorption coefficients demonstrated a similar pattern, ranging from 12 to 140. In all six soils the adsorption Kd values decreased with Increasing rate of application of the test substance. This is probably due to some saturation of the stronger adsorption sites. However, at no concentration did further adsorption cease, even at the highest rate of application which was equivalent to 40 µg of the test substance/g of soil. The Freundlich equation showed a good fit In all six soils with r2 values always greater than 0.97. The Freundlich equation 1 /n values, which ranged from 0.89 ('Gayton') to 0.97 ('East Anglia'), suggested a slight decrease in adsorption with Increasing rate of application, supporting those data derived from the Kd values. Average Kd values adjusted for the organic carbon content of soil (Koc values) ranged from 1,200 in the high pH loamy sand soil to 11,000 in the low pH silty clay loam soil. Similar coefficients derived from the Freundlich adsorption coefficient (K' oc: values) followed the same pattern ranging from 950 to 8,500. Using the McCall Classification System to assess potential mobility in soil, the test substance can be
classified as having between 'low potential mobility' and being 'Immobile' In soil. The results suggested that in the lower pH soils ('Lilly Field', 'Nebo' and 'Salmonds Bridge') adsorption of the test substance was related to the clay content. At these lower pH values there was no apparent relationship between the adsorption of this compound and the organic matter content of soil eg average Kd value 'Salmonds Bridge' 52 at an organic matter content of 3.3% versus 'Nebo' average Kd value 180 and % organic matter content 2.8. Conversely, in the higher pH soils it did appear that there might be relationship between adsorption and organic matter content.
This pattern of adsorption of the test substance may be related to the physicochemical properties the compound. The test substance has a pKb of approximately 3.8. the molecule becoming progressively more protonated as pH decreases. As the compound becomes protonated it is likely to be more attracted to negatively charged clay surfaces. However, at higher pH values, under which circumstance only the neutral form will exist, the compound will be more lypophillc in nature and therefore attracted largely to organic matter in soil.

- Desorption of 14C-labelled test substance from Soil:
Kd values generally increased during the single desorption step, with average increases ranging from -4 (within experimental error of zero) to 270. Increases in the adsorption coefficients were most pronounced in those soils in which initial adsorption was least. For example in the 'Nebo' soil (average Kd value adsorption step 180) there was no increase In Kd values after the desorption step versus the 'Lilly Field' soil (average Kd value at the adsorption step 15) in which the average percentage increase Kd values after the desorption step was 270. These data suggest that the adsorption of the test substance to soil is not generally entirely reversible, resulting in further reduction in the potential mobility of the compound. This tendency towards non-reversible adsorption was also reflected by increases in the average K'oc values, which after the desorption step ranged from 1,300 to 8,800. Using the McCall Classification scale the potential soil mobility of the test substance is reduced further to between 'low' and being 'immoblle'.

Table 4. Synopsis of Mass Balance Results from the Adsorption/Desorption Samples for 'Gayton' Soil.

Nominal Rate Applied Aqueous Phase	Total DPS Applied	DPS in Adsorption Aqueous	DPS* In Desorption Aqueous	DPS in Soil Extract	Residual DPS on Soil Combustion	Total DPS Recovered	Percentage of Applied Recovered
0.04	6180	3020	-	2900	28	5950	96
0.04	6180	2200	1040	1160	15	4410	72
0.1	15700	6930	-	7110	85	14100	90
0.1	15700	7600	3310	4070	56	15000	96
2	15500	6160	-	5550	51	11800	76
0.2	15500	7560	3090	2940	47	13600	90
1.0	15200	8150	-	6850	74	15100	99
1.0	15200	7890	3190	3410	53	14500	96
2.0	15500	8170	-	6280	55	14500	94
2.0	15500	8240	3170	2950	38	14400	93

* Desorption only samples

  Table 5. Synopsis of Mass Balance Results from the Adsorption/Desorption Samples for 'Salmonds Bridge' Soil.

Nominal Rate Applied Aqueous Phase	Total DPS Applied	DPS In Adsorption Aqueous	DPS* In Desorption Aqueous	DPS in Soil Extract	Residual DPS** on Soil Combustion	Total DPS Recovered	Percentage of Applied Recovered
0.04	6,180	2,100	-	3,770	-	5,860	95
0.04	6,180	2,130	1,210	2,630	-	5,970	97
0.1	15,700	5,560	-	9,290	-	14,800	95
0.1	15,700	5,460	3,110	5,950	-	14,500	93
0.2	15,500	5,690	-	9,140	-	15,300	96
0.2	15,500	5,770	3,320	6,550	-	15,200	95
1.0	15,200	6,190	-	8,360	-	15,100	96
1.0	15,200	6,220	3,150	5,210	-	15,100	96
2.0	15,500	6,280	-	8,330	-	15,000	94
2.0	15,500	6,220	3,340	5,420	-	15,400	96

* Desorption only samples.

** No soil combustion results (scintillation cocktail ran out during combustion process), As there was virtually no chemical in soil after the extraction process in all other soils tested this was deemed of no consequence.

Table 6. Synopsis of Mass Balance Results from the Adsorption/Desorption 0.2 µg Samples for the Remaining Solis 

Soil	Total DPS Applied	DPS In Adsorption Aqueous	DPS* in Desorption Aqueous	DPS in soil Extract	Residual DPS on Soil Combustion	Total DPS Recovered	Percentage of Applied Recovered
'Kenny Hill'	13,700	4,440	-	9,010	55	13,500	99
..	13,700	4,320	2750	6,240	38	13,300	98
'East Anglia'	13,700	5,640	-	7,830	28	13,500	99
..	13,700	6,130	3190	3,940	15	13,300	97

* Desorption only samples.

Table 7. Synopsis of Mass Balance Results from the Adsorption/Desorption Samples of 'Lilly Field' Soil

Nominal Rate Applied Aqueous Phase	Total DPS Applied	DPS in Adsorption Aqueous	DPS* In Desorption Aqueous	DPS In Soil Extract	Residual DPS** on Soll Combustion	Total DPS Recovered	Percentage of Applied Recovered
0.04	5,400	3,900	-	1,400	33	5,300	99
0.04	5,400	3,800	870	410	17	5,100	94
0.1	13,600	9,300	-	3,900	62	13,200	98
0.1	13,600	7,600	1,300	670	26	9,600	71
0.2	13,700	9,100	-	3 ,30 0	-	12,500	91
0.2	13,700	10,000	2,400	1,100	-	13,500	100
1.0	13,500	6,000	-	4,700	-	7,700	58
1.0	13,500	9,700	2,400	1,200	-	13,300	99
2.0	13,800	7,800	-	2,300	-	10,100	73
2.0	13,800	10,400	1,900	900	-	13,200	96

* Desorption only samples

** No soil combustion results (scintillation cocktail ran out during combustion process). As there was virtually no chemical In soil after the extraction process In all other soils tested this was deemed of no consequence.

Table 8. Synopsis Mass Balance Results from the Adsorption/Desorption Samples for 'Nebo' Soil

Nominal Rate Applied Aqueous Phase	Total DPS Applied	DPS In Adsorption Aqueous	DP* In Desorption Aqueous	DPS In Soll Extract	Residual DPS** on Soil Combustion	Total DPS Recovered	Percentage of Applied Recovered
0.04	6,200	750	-	5,300	-	6,100	99
0.04	6,200	720	670	4,500	-	5,900	95
0.1	15,700	2,000	-	13,100	-	15,000	96
0.1	15,700	1,900	1,600	11,400	-	14,800	95
0.2	15,500	2,000	-	13,200	-	15,200	98
0.2	15,500	2,000	1,700	11,100	-	14,800	96
1.0	15,200	2,200	-	12,600	-	14,800	97
1.0	15,200	2,300	2,000	10,100	-	14,300	93
2.0	15,500	2,200	-	12,500	-	14,700	95
2.0	15,500	2,200	2,000	10,400	-	14,700	95

* Desorption only samples

** No soil combustion results (scintillation cocktail ran out during combustion process). As there was virtually no residual 14C-labelled chemical In other all soil samples after the extraction process it was considered that this would not greatly affect the results.

Table 9. Concentrations of the test substance in Aqueous and Soil Phases after Adsorption Step and Resultant Kd Values.

Soil	Nominal Rate Applied (µg/cm3)	Concentration in Aqueous Phase (µg/cm3)	Concentration Adsorbed to Soil Phase (µg/g)	Kd
'Kenny Hill'	0.04	0.013	0.54	43
	0.1	0.033	1.3	40
	0.2	0.067	2.7	40
	1.0	0.37	13	34
	2.0	0.78	25	32
'Gayton'	0.04	0.021	0.50	26
	0.1	0.057	1.2	21
	0.2	0.11	2.3	22
	1.0	0.62	10	16
	2.0	1.3	20	16
'East Anglia'	0.04	0.016	0.47	30
	0.1	0.040	1.2	30
	0.2	0.090	2.2	25
	1.0	0.45	11	24
	2.0	0.85	24	28
'Lilly Field'	0.04	0.016	0.29	22
	0.1	0.051	0.64	13
	0.2	0.11	1.1	10
	1.0	0.44	7.1	18
	2.0	1.1	12	12
'Nebo'	0.04	0.0038	0.80	210
	0.1	0.011	2.0	190
	0.2	0.021	3.9	190
	1.0	0.12	19	150
	2.0	0.24	39	160
'Salmonds Bridge'	0.04	0.0092	0.59	64
	0.1	0.026	1.5	56
	0.2	0.055	2.8	51
	1.0	0.29	13	44
	2.0	0.60	27	44

Table 10. Concentrations of the test substance in Aqueous and Soil Phases after Desorption Step and Resultant Kd Values

Soil	Nominal Rate Applied (µg/cm3)	Concentration in Aqueous Phase (µg /cm3)	Concentration Adsorbed to Soil Phase (µg/g)	Kd
'Kenny Hill'	0.04	0.0076	0.40	53
	0.1	O.019	0.99	53
	0.2	0.042	1.9	47
	1.0 2.0	0.20 0.39	8.7 18	43 48
'Gayton'	0.04	0.0082	0.41	51
	0.1	0.027	0.67	25
	0.2	0.045	1.5	34
	1.0	0.25	5.9	24
	2.0	0.49	12	24
'East Anglia'	0.04	0.0092	0.30	33
	0.1	0.017	0.94	57
	0.2	0.047	1.40	30
	1.0	0.21	6.9	34
	2.0	0.36	17	48
'Lilly Field'	0.04	0.0035	0.27	131
	0.1	0.0089	0.57	66
	0.2	0.026	0.46	18
	1.0	0.099	4.8	82
	2.0	0.22	4.2	19
'Nebo'	0.04	0.0041	0.71	180
	0.1	0,0087	1.8	210
	0.2	0.020	3.4	170
	1.0	0.099	16	160
	2.0	0.21	33	150
'Salmonds Bridge'	0.04	0.0050	0.41	82
	0.1	0.014	1.0	74
	0.2	0.028	1.9	67
	1.0	0.14	8.4	60
	2.0	0.31	17	55

Table 11. Summary of Kd, K', Koc and K'oc Values from the Adsorption Step for the test substance

Soil	Nominal Rate Applied Aqueous Phase (µg/cm3)	Kd	Koc	K'	K'oc
'Kenny Hill' %OM=5.1 pH=7.9 %Clay=12	0.04	43	1,500	32	1,100
	0.1	40	1,400
	0.2	40	1,400
	1.0	34	1,200
	2.0	32	1,100
Average Values		38	1,300
'Gayton' %OM=2.7 pH=7.9 %Clay=11	0.04	26	1,500	16	950
	0.1	21	1,200
	0.2	22	1,300
	1.0	16	970
	2.0	16	940
Average Values		20	1,200
'East Angila' %OM=2.9 pH=7.8 %Clay=11	0.04	30	1,800	25	1,500
	0.1	30	1,800
	0.2	25	1,500
	1.0	24	1,400
	2.0	28	1,700
Average Values		27	1,600
'Lilly Field' %OM=0.5 pH=S.5 %Clay=4	0.04	22	7,600	12	4,100
	0.1	13	4,500
	0.2	10	3,500
	1.0	18	6,300
	2.0	12	4,100
Average Values		15	5,200
'Nebo' %OM=2.8 pH=4.9 %Clay=28	0.04	210	13,000	140	8,500
	0.1	190	12,000
	0.2	190	12,000
	1.0	150	9,400
	2.0	160	9,800
Average Values		180	11,000
'Salmonds Bridge' %OM=3.3 pH=4.7 %Clay=18	0.04	64	3,300	40	2,100
	0.1	56	2,900
	0.2	51	2,600
	1.0	44	2,300
	2.0	44	2,300
Average Values		52	2,700

 

Table 12. Summary of 1 /n and r2 Values from the Freundlich Equations for the test substance

Soil	1/n	r2
'Kenny Hill'	0.93	1.00
'Gayton'	0.89	1.00
'East Anglia'	0.97	1.00
'Lilly Field'	0.94	0.98
'Nebo'	0.95	1.00
'Salmonds Bridge'	0.91	1.00

 

Table 13. Summary of Kd, K' and K'oc values from the Desorption Step and the Percentage Increase in Kd Values from Adsorption Step to Desorption Step

Soil	Nominally Applied Rate (µg/cm3)	Kd	K'	K'oc	% Increase in Kd Value Adsorption to Desorption
'Kenny Hill' %OM=5.1 pH=7.9 %Clay=12	0.04	53	43	1,500	22
	0.1	53			33
	0.2	47			16
	1.0	43			25
	2.0	48			49
Average Values		49			29
'Gayton' %OM=2.7 pH=7.9 %Clay=11	0.04	51	20	1,300	98
	0.1	25			22
	0.2	34			5B
	1.0	24			47
	2.0	24			51
Average Values		32			55
'East Anglia' %OM=2.9 pH=7.8 %Clay=11	0.04	33	39	2,300	10
	0.1	57			90
	0.2	30			18
	1.0	34			39
	2.0	48			71
Average Values		40			46
'Lilly Field' %OM=0.5 pH=5.5 %Clay=4	0.04	120	15	5,000	460
	0.1	66			400
	0.2	18			77
	1.0	82			350
	2.0	19			58
Average Values		62			270
'Nebo' %OM=2.8 pH=4.9 %Clay=28	0.04	180	140	8,800	-17
	0.1	210			8
	0.2	170			-10
	1.0	160			5
	2.0	150			-4
Average Values		170			4
'Salmonds Bridge' %OM=3.3 pH=4.7 %Clay=18	0.04	82	49	2,600	28
	0.1	74			33
	0.2	67			33
	1.0	60			35
	5.0	55			25
Average Values		6B			31

Table 14. Percentage of 14C-labelled test substance in the Soil After Adsorption Step and Percentage of Adsorbed Desorbed.

Soil	Nominally Applied Rate (µg/cm3)	Percentage of Applied test substance Adsorbed to Soil After Adsorption Step	Percentage of Adsorbed Desorbed
'Kenny Hill'	0.04 0.1 0.2 1.0 2.0	68 67 67 63 62	26 26 28 30 27
Average Values		65	27
'Gayton'	0.04 0.1 0.2 1.0 2.0	55 51 52 45 44	26 41 34 42 42
Average Values		49	37
'East Anglia'	0.04 0.1 0.2 1.0 2.0	60 60 55 55 58	36 24 38 36 27
Average Values		58	32
'Lilly Field'	0.04 0.1 0.2 1.0 2.0	37 32 27 36 30	29 24 56 35 50
Average Values		32	39
'Nebo'	0.04 0.1 0.2 1.0 2.0	88 87 86 84 85	11 12 13 15 15
Average Values		86	13
'Salmonds Bridge'	0.04 0.1 0.2 1.0 2.0	64 63 61 57 58	30 31 32 35 35
Average Values		61	33

Validity criteria fulfilled:

yes

Conclusions:

The test substance was strongly adsorbed in the six soils studied: 'Gayton', 'Kenny HilI' and 'East Anglia' (loamy sands), 'Lilly Field' (sand), 'Salmonds Bridge' (sandy loam) and 'Nebo' (silty clay loam). Average Kd values in the six soils ranged from 15 in the sand soil ('Lilly Field') to 180 in the silty clay loam soil ('Nebo'). Freundlich adsorption coefficients (K') followed a similar pattern, ranging from 12 to 140. The Freundlich equation showed a good fit in all six soils with r2 values always greater than 0.97. The Freundlich equation 1 /n values, which ranged from 0.89 ('Nebo') to 0.97 ('East Angila'), suggested a slight decrease in adsorption with increasing rate of application, supporting those data derived from the Kd values.
Average Kd values adjusted for the organic carbon content of soil (Koc values) ranged from 1,200 in the high pH loamy sand soil to 11,000 in the low pH silty clay loam soil. Coefficients derived from the Freundlich adsorption coefficient (K'oc values) followed the same pattern ranging from 950 to 8,500. Using the McCall classification system to assess potential mobility in soil, the potential mobility of the test substance can be classified as being between 'low' and 'immobile' in soil.
The data showed a strong correlation between the adsorption of the test substance to soil and % clay content, this being particularly strong at lower pH's when the pKb of the compound would suggest that it would be protonated and therefore attracted to negatively charged clay surfaces. In the higher pH soils adsorption appeared to be related to the organic matter content of soil, at these pHs the compound would be expected to be neutral. Kd values increased during the single desorption step (average increases in Kd values ranging -4 to 270%) suggesting that the adsorption of the compound to soil is not entirely reversible, indicating a further reduction in the potential mobility of the compound. This was also reflected by the desorption K'oc values which ranged from 1,300 to 8,800. Using the adsorption/desorption properties measured In this study in conjunction with the previously described degradation rate of the chemical in soil (half-life less than 1 month), it may be concluded that the test substance will have a very low potential to leach to groundwater.

Executive summary:

The adsorption and desorption properties of radiolabelled test substance was studied in six pre-sterilized soils. The study was conducted in accordance with OECD TG106 and was in compliance with GLP criteria. In this study, the test substance was added to soil:water slurries at five rates of application (0.04, 0.1, 0.2, 1.0 and 2.0μg/cm3). This soil:water ratio was chosen due to the high adsorption of the compound. The adsorption stage lasted for 24 hrs and the desorption stage was conducted for 24 hrs as well. The temperature of both stages was 20 ± 2˚C. The extracts were analysed by LSC and TLC to quantify total radioactivity recovered.The residual soil was dried at room temperature and the radioactivity remaining on the soil was determined by combustion.

 

The results show that average Kd values in the six soils ranged 15 in the sand to 180 in the silty clay loam. Freundlich adsorption coefficients (Kf) followed a similar pattern, ranging from 12 to 140. The Freundlich equation showed a good fit in all six soils with r2 values always greater than 0.97 and 1/n values always greater than 0.89 demonstrating nearly linear isotherms. Average Kd values adjusted for the organic carbon content of soil (Koc values) ranged from 1,200 in the high pH loamy sand to 11,000 in the low pH silty clay loam. Coefficients derived from the Freundlich adsorption coefficient (Kfoc values) followed the same pattern ranging from 950 to 8,500.

 

Using the McCall Classification scale to assess potential mobility in soil, the test substance can be classified as having between 'low' potential mobility and being 'immobile'.

Reference 2

Endpoint:

adsorption / desorption, other

Remarks:

batch equilibrium method

Type of information:

experimental study

Adequacy of study:

key study

Study period:

29 Jun 2000 to 14 Jul 2000

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

Deviations:

not specified

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

20 °C

Analytical monitoring:

yes

Details on sampling:

- Analysis of aqueous and soil phase (absorption): water slurries were analysed for radioactivity content after the completion of the adsorption step.
- Analysis of aqueous and soil phase (desorption): The soil and aqueous solution in the following tubes at the end of the desorption phase were analysed.

Matrix no.:

#1

Matrix type:

sandy loam

% Clay:

16

% Silt:

27

% Sand:

57

% Org. carbon:

1.7

pH:

5.8

CEC:

11.9 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

loam

% Clay:

27

% Silt:

42

% Sand:

31

% Org. carbon:

1.4

pH:

5.6

CEC:

10.7 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

loam

% Clay:

16

% Silt:

36

% Sand:

48

% Org. carbon:

3.6

pH:

6.5

CEC:

31.3 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

sandy loam

% Clay:

16

% Silt:

29

% Sand:

55

% Org. carbon:

1.7

pH:

5.9

CEC:

25.2 meq/100 g soil d.w.

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: See Table 1 in 'Any other information on materials and methods incl. tables'
- Soil preparation: The soil was air-dried and 2 mm sieved. Prior to treatment with radiolabelled test substance air-dried soil samples were equilibrated for at least 18 hours in glass vessels with 0.01 M aqueous CaCl2. Tubes contained a weight of soil equivalent to 1 g oven dried weight and approximately 20 mL CaCl2. The amounts of soil added were such that after the addition of the respective radiochemical solution the ratio of soil (oven dried weight) to aqueous solution would be 1 : 20. Equilibration of the soil slurry was achieved by continuous shaking on an orbital shaker at approximately 50 revolutions per minute (rpm) at 20°C in darkness. The use of 0.01 M CaCl2 solution simulated the salt concentration normally found in soils and prevented dispersion of the clay colloids.
- Storage: The soils were stored at 4°C before the test .

PROPERTIES
See Table 2 in 'Any other information on materials on methods. incl. tables'.

Details on test conditions:

TEST SYSTEM AND CONDITION (Adsorption Experiment)
- Reaction vessel: Glass vessels
- Amount of soil and water per treatment: See Table 5 in 'Any other information on materials and methods incl. tables'
- Soil to aqueous solution ration: 1:20
- Number of reaction vessels/concentration: 2
- Method of preparation of test solution: The liquid 14C-labelled test substance as received was dissolved in ethyl acetate (25 mL). This was quantified by LSC. The 14C-labelled test substance was used in the study as supplied, without any radiodilution.
Separate treatment solutions were prepared for each of the treatment concentrations in order to achieve initial aqueous phase solution concentrations of 0.05, 0.1, 0.2, 1.0 and 2.0 μg/mL after application. To prepare the treatment solutions an appropriate volume of the stock solution was removed to a glass vial. The solvent was then removed by evaporation under nitrogen. Acetonitrile was then added to dissolve the radiochemical.
- Method of applying the test solution: Aliquots (20 μL, 40 μL for highest dose level) of the appropriate 14C-labelled test substance treatment solution were applied to pre-equilibrated soil : water slurries. Additional aliquots (20 μL) of 0.2, 0.1 and 0.05 μg/mL dose solutions were quantified by LSC to check the homogeneity of the treatment solutions and to determine the application rate. At the higher dose levels aliquots (20 μL) were diluted to 5 mL and aliquots (200 μL) analysed by LSC.
- Treatment of soil slurries: The test solution treated soil slurries were placed on orbital shakers (approximately 50 rpm) for 2 hours. The equilibration time was determined by the 'preliminary' experiment. Samples were equilibrated at 20°C in darkness.

TEST PROCEDURE (desorption Experiment)
After adsorption test, all tubes were taken through one desorption procedure. A volume of fresh aqueous CaCl2 solution equivalent to that removed after the adsorption phase (17 or 18 mL) was then added to the soil remaining in each tube. The resultant samples were replaced on the
orbital shaker and equilibrated at 20°C for 2 hours. The samples were centrifuged. A volume of the aqueous supernatant (17 or 18 mL, equivalent to the volume removed at the adsorption phase) was removed and quantified by LSC.

PRELIMARY EXPERIMENT
In a 'preliminary' experiment using 'Kochi' soil, the time taken for the test substance to equilibrate between the soil and solution phases was studied over a period of 48 hours, using a single treatment rate (0.2 μg/mL). A mass balance of radioactivity was obtained from a selected sample in the preliminary experiment to confirm that all the test substance was accounted for after completion of equilibration.

Duration:

2 h

Temp.:

20 °C

Remarks:

Nominal initial concentrations in the aqueous phase of 0.05, 0.1, 0.2, 1.0 and 2.0 μg/mL.

Duration:

2 h

Temp.:

20 °C

Key result

Sample No.:

#1

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

1 310 L/kg

pH:

5.8

Temp.:

20 °C

Matrix:

Sandy loam

% Org. carbon:

1.7

Key result

Sample No.:

#2

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

1 990 L/kg

pH:

5.6

Temp.:

20 °C

Matrix:

Loam

% Org. carbon:

1.4

Key result

Sample No.:

#3

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

737 L/kg

pH:

6.5

Temp.:

20 °C

Matrix:

Loam

% Org. carbon:

3.6

Key result

Sample No.:

#4

Type:

Koc

Remarks:

Freundlich Coefficients

Value:

1 270 L/kg

pH:

5.9

Temp.:

20 °C

Matrix:

Sandy loam

% Org. carbon:

1.7

Sample No.:

#1

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

2 890 L/kg

Temp.:

20 °C

pH:

5.8

Matrix:

Sandy loam

% Org. carbon:

1.7

Sample No.:

#2

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

3 820 L/kg

Temp.:

20 °C

pH:

5.6

Matrix:

Loam

% Org. carbon:

1.4

Sample No.:

#3

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

1 430 L/kg

Temp.:

20 °C

pH:

6.5

Matrix:

Laom

% Org. carbon:

3.6

Sample No.:

#4

Phase system:

solids-water in soil

Type:

other: Koc - Desorption Freundlich Coefficients

Value:

2 650 L/kg

Temp.:

20 °C

pH:

5.9

Matrix:

Sandy loam

% Org. carbon:

1.7

Adsorption and desorption constants:

See Table 9 and Table 10 in 'Any other information on results incl. tables'.

Recovery of test material:

- Mass Balance: Recoveries ranged from 89.5 to 98.2% with a mean value of 94. 7%. These recoveries, together with those from the 'preliminary' experiment show a good correlation between radiolabelled material applied and that recovered. See Table 6 in 'Any other information on results incl. tables'.

Concentration of test substance at end of adsorption equilibration period:

See Table 7 in 'Any other information on results. incl. tables'

Concentration of test substance at end of desorption equilibration period:

See Table 8 in 'Any other information on results. incl. tables'

Sample no.:

#1

Duration:

2 h

% Adsorption:

54.92

Remarks on result:

other: Average % adsorption

Sample no.:

#2

Duration:

2 h

% Adsorption:

60.22

Remarks on result:

other: Average % adsorption

Sample no.:

#3

Duration:

2 h

% Adsorption:

58.94

Remarks on result:

other: Average % adsorption

Sample no.:

#4

Duration:

2 h

% Adsorption:

54.04

Remarks on result:

other: Average % adsorption

Sample no.:

#1

Duration:

2 h

% Desorption:

16

Remarks on result:

other: in supernatant removed; 0.2 μg/mL

Sample no.:

#2

Duration:

2 h

% Desorption:

15.8

Remarks on result:

other: in supernatant removed; average % desorption

Sample no.:

#3

Duration:

2 h

% Desorption:

15.8

Remarks on result:

other: in supernatant removed; 0.2 μg/mL

Sample no.:

#4

Duration:

2 h

% Desorption:

16.6

Remarks on result:

other: in supernatant removed; 0.2 μg/mL

Transformation products:

not measured

Details on results (Batch equilibrium method):

An overview of the results is provided in Table 6 - Table 10 in 'Any other information on results incl. tables'
- Stability of the test substance in the Test System: There was no significant degradation of the test substance in either aqueous or solid phases. In the aqueous phases, the purity of 14C-labelled test substance ranged from 90.3 to 96.8%. The purity of 14C-labelled test substance in the soil extracts ranged from 91.2 to 98.4%. For the purpose of calculating the adsorption and desorption coefficients, the radioactivity content in the solutions and soils was not corrected for the purity of the test substance.

- Adsorption of the test substance: After 2 hours equilibration with a soil: water (0.01 M aqueous CaCl2 solution) ratio of 1 : 20 a range of 51.3 to 65.7% (mean values) of the applied chemical was adsorbed to the soil. Average adsorption partition coefficients (Kd) ranged from 23.7 for the 'Ushiku' soil type to 30.6 for the 'Kechi' soil type. The Freundlich adsorption coefficients (KF) demonstrated a similar pattern and ranged from 22.1 ('Ushiku') to 27.6 ('Kochi'). The linear regression of the Freundlich equation showed a good fit for all the soils tested with r2 (the covariance) values greater than or equal to 0.99. 1/n values (the slope of the line) which ranged from 0.96 to 0.97, demonstrated that the adsorption of the test substance was nearly linear across the concentration range tested. Average Koc values (Kd adjusted for the soil organic carbon) ranged from 804 in the 'Tsukuba' soil to 2200 in the 'Kochi' soil. KFoc values (derived from KF) followed a similar pattern and ranged from 737 to 1990. Using the McCall Classification scale to assess potential mobility, the test substance can be classified as having a low mobility in soil.

- Desorption of the test substance: Average Kd values for the desorption ranged from 47.3 to 53.5. The Kd, Koc and KFoc values after the desorption step were all higher than those after the adsorption step, the increase being from 58 to 126%. These data therefore suggest that adsorption of the test substance is nearly non-reversible, resulting in a reduction in the potential
mobility of the compound. Generally the potential mobility classification of the test substance changed from low to slight after the desorption step. The apparent desorption coefficients (KFdes) again showed that the adsorption was not entirely reversible.

Table 6. Synopsis of Mass Balance Data from the Selected Samples Treated with 14C-labelled test substance after the Desorption Phase

Soil	Nominal Initial Aqueous Phase Concentration of the test substance (µg/mL )	Sample Identity	Total in Supernatant Removed (% AR)		Total in Soil Extracts (%AR)	Total in Soil Debris (%AR)	Total Recovered (%AR)
			Adsorption	Desorption
'Kagoshima'	0.2	KA/0.2/50	41.5	16.0	38.1	0.4	96.0
'Kochi'	2	KO/2/13	36.2	15.2	39.2	2.0	92.6
	1	K0/1/15	37.0	14.8	35.3	2.4	89.5
	0.2	KO/0.2/54	37.3	16.9	38.0	2.2	94.4
	0.1	KO/0.1/56	35.4	16.6	42.0	2.1	96.1
	0.05	KO/0.05/21	30.2	15.5	46.6	2.4	94.7
'Tsukuba'	0.2	TS/0.2/58	38.0	15.8	41.6	0.9	96.3
'Ushiku'	0.2	US/0.2/62	42.3	16.6	38.5	0.8	98.2

AR       Applied radioactivity

Table 7. Concentrations of the test substance in Aqueous and Soil Phases after Adsorption, Resultant Kd Values and % Applied Adsorbed

Soil	Nominal Rate Applied (µg/mL)	Concentration in Aqueous Phase (µg/mL)	Concentration in Soil Phase (µg/g)	Kd	% Applied Adsorbed
'Kagoshima' %OC= 1.7 pH=5.8 CEC= 11.9	0.05	0.0213	0.5920	27.9	58.2
	0.1	0.0466	1.1474	24.7	55.1
	0.2	0.1001	2.1440	21.4	51.6
	1.0	0.4268	10.9924	25.8	56.3
	2.0	0.9087	19.3586	21.3	53.4
'Kochi' %OC= 1.4 pH=5.6 CEC = 10.7	0.05	0.0175	0.6679	38.3	65.7
	0.1	0.0424	1.2260	29.0	59.1
	0.2	0.0897	2.3317	26.1	56.7
	1.0	0.3949	11.6358	29.5	59.6
	2.0	0.7820	23.4289	30.0	60.0
'Tsukuba' %OC=3.6 pH= 6.5 CEC = 31.3	0.05	0.0186	0.6448	34.7	63.4
	0.1	0.0441	1.1916	27.1	57.5
	0.2	0.0884	2.3676	26.9	57.2
	1.0	0.3999	11.5274	28.8	59.0
	2.0	0.8285	22.4816	27.2	57.6
'Ushiku' %OC= 1.7 pH=5.9 CEC=25.2	0.05	0.0207	0.6043	29.3	59.4
	0.1	0.0505	1.0649	21.1	51.4
	0.2	0.1011	2.1311	21.1	51.3
	1.0	0.4430	10.6902	24.1	54.7
	2.0	0.9124	20.8558	22.9	53.4

Note:

Concentrations are the mean value of 2 replicates

Kd=mean of Kd of each replicate ≠ mean Cs/Caq

Table 8. Concentrations of the test substance in Aqueous and Soil Phases after desorption, Resultant Kd Values ,% increases in Kd value between adsorption and desorption and Kfdes values

Soil	Nominal Rate Applied (µg/mL)	Concentration in Aqueous Phase (µg/mL)	Concentration in Soil Phase (µgig)	Kd	% Increased in Kd (a)	KFdes (b)
'Kagoshima' %OC= 1.7 pH=5.8 CEC= 11.9	0.05	0.0085	0.4860	57.3	106.0	85.2
	0.1	0.0197	0.8925	45.3	84.0
	0.2	0.0376	1.6915	45.1	110.0
	1.0	0.1634	9.0132	55.3	115.0
	2.0	0.3294	15.8027	48.1	126.0
'Kochi' %OC= 1.4 pH=5.6 CEC = 10.7	0.05	0.0088	0.5282	60.4	58.0	71.8
	0.1	0.0190	0.9314	49.0	69.0
	0.2	0.0372	1.7706	47.7	83.0
	1.0	0.1634	9.1621	56.1	90.0
	2.0	0.3366	18.2677	54.3	81.0
'Tsukuba' %OC=3.6 pH= 6.5 CEC = 31.3	0.05	0.0093	0.5155	55.8	61.0	83.5
	0.1	0.0200	0.9252	46.4	72.0
	0.2	0.0397	1.8413	46.4	73.0
	1.0	0.1808	9.1197	50.5	75.0
	2.0	0.3379	18.2270	54.0	99.0
'Ushiku' %OC= 1.7 pH=5.9 CEC=25.2	0.05	0.0087	0.4934	57.1	95.0	78.0
	0.1	0.0198	0.8197	41.4	96.0
	0.2	0.0404	1.6238	40.2	91.0
	1.0	0.1755	8.5019	48.5	101.0
	2.0	0.3394	16.7895	49.5	116.0

(a)       % Increase in Kd value between adsorption and desorption steps

(b)       Apparent Soil Desorption Coefficient

Table 9.Summary of Adsorption Coefficients (Kd, Koc, KF, KFoc and 1/n Values) for the test substance

Soil	Nominal Rate Applied to Aqueous Phase (µg/mL)	Kd	Koc	KF	KFoc	1/n
'Kagoshima' %OC= 1.7 pH=5.8 CEC = 11.9	0.05	27.9	1660	22.0	1310	0.96
	0.1	24.7	1470
	0.2	21.4	1270
	1.0	25.8	1530
	2.0	21.3	1270
Average values		24.2	1440
'Kochi' %OC= 1.4 pH=5.6 CEC= 10.7	0.05	38.3	2750	27.6	1990	0.96
	0.1	29.0	2080
	0.2	26.1	1870
	1.0	29.5	2120
	2.0	30.0	2150
Average values		30.6	2200
'Tsukuba' %OC=3.6 pH= 6.5 CEC = 31.3	0.05	34.7	965	26.5	737	0.96
	0.1	27.1	752
	0.2	26.9	748
	1.0	28.8	802
	2.0	27.2	755
Average values		28.9	804
'Ushiku' %OC= 1.7 pH=5.9 CEC=25.2	0.05	29.3	1680	22.1	1270	0.97
	0.1	21.1	1210
	0.2	21.1	1210
	1.0	24.1	1390
	2.0	22.9	1310
Average values		23.7	1360

 

Table 10.Summary of desorption Coefficients (Kd, Koc, KF, KFoc and 1/n Values) for the test substance

Soil	Nominal Rate Applied to Aqueous Phase (µg/mL)	Kd	Koc	KF	KFoc	1/n
'Kagoshima' %OC= 1.7 pH=5.8 CEC = 11.9	0.05	57.3	3400	48.6	2890	0.99
	0.1	45.3	2690
	0.2	45.1	2680
	1.0	55.3	3290
	2.0	48.l	2860
Average values		50.2	2980
'Kochi' %OC= 1.4 pH=5.6 CEC= 10.7	0.05	60.4	4340	53.1	3820	1.00
	0.1	49.0	3530
	0.2	47.7	3420
	1.0	56.1	4030
	2.0	54.3	3900
Average values		53.5	3840
'Tsukuba' %OC=3.6 pH= 6.5 CEC = 31.3	0.05	55.8	1550	51.4	1430	1.01
	0.1	46.4	1290
	0.2	46.4	1290
	1.0	50.5	1410
	2.0	54.0	1500
Average values		50.6	1410
'Ushiku' %OC= 1.7 pH=5.9 CEC=25.2	0.05	57.1	3280	46.2	2650	0.99
	0.1	41.4	2380
	0.2	40.2	2310
	1.0	48.5	2790
	2.0	49.5	2840
Average values	0.05	47.3	2720

Validity criteria fulfilled:

yes

Conclusions:

The test substance was strongly adsorbed to all soils tested. Freundlich adsorption constants adjusted for soil organic carbon content (KFoc) ranged from 737 to 1990. According to the McCall Classification scale to assess a chemical's mobility, the test substance can be classified as having a low mobility in soil. Kd, Koc, KF and KFoc values all increased during the single desorption step, indicating that the adsorption of the test substance is almost non-reversible.

Executive summary:

The adsorption/desorption characteristics of [14C]-labelled test substance were studied in 4 different Japanese soils: Kagoshima (sandy loam), Kochi (Loam), Tsukuba (Loam) and Ushiku (Sandy loam) using a standard batch equilibrium method, in the dark at 20°C. The study was conducted in according to OCED TG 106 and was in compliance with GLP. The soils used had a pH in the range 5.6 to 6.5 and an organic carbon contents in the range 1.4 to 3.6%.

Preliminary experiments were conducted to ascertain the time required to achieve an equilibrium between the test substance in solution and adsorbed to soil and to confirm that an appropriate soil : solution ratio was used for the definitive experiments. These experiments indicated a soil : solution ratio of 1 g : 20 mL was appropriate and that equilibration had occurred by 2 hours. For the definitive experiment, radiolabelled test substance was added to soil : water slurries resulting in a final ratio of 1 g soil : 20 mL aqueous solution. A range of five nominal rates of application was achieved in the definitive experiment (0.05, 0.1, 0.2, 1.0 and 2.0 μg/mL). The adsorption step was followed by one desorption step.

The calculated Freundlich adsorption coefficients (KF) ranged from 22.1 to 27.6 L/kg, while the 1/n values ranged from 0.96 to 0.97. When corrected for the organic carbon content of the soils, the resultant KFoc values ranged from 737 to 1990 L/kg. The mean partition coefficients Kd ranged from 23.7 to 30.6 mL/g with the corresponding KOC des of 804 to 2200 mL/g. The calculated Freundlich desorption coefficients (KF,des) ranged from 46.2 to 53.1 mL/g, while the 1/n values ranged from 0.99 to 1.01. When corrected for the organic carbon content of the soils, the resultant KFOC des values ranged from 1430 to 3820 mL/g. The mean partition coefficients Kd des ranged from 47.3 to 53.5 mL/g with the corresponding KOC des of 1410 to 3840 mL/g. According to the McCall Classification scale to assess a chemical's mobility, the test substance can be classified as having a low potential mobility in soil. Kd, Koc, Kp and Kroc values all increased during the desorption step, indicating that the adsorption of the test substance is almost non-reversible.

Description of key information

Average Log Koc = 3.37 (Koc = 2356) based on two studies covering 10 soils, equilibrium batch method, OECD TG 106, Winwick 2000 and Hartfree et al. 1993.

Key value for chemical safety assessment

Koc at 20 °C:

2 356

Additional information

Table. Summary of the Kfoc values for the substance

USDA	Name/Origin	OC (%)	pH	Kf (mL/g)	Kfoc (mL/g)	1/n	Author / Year
Loamy sand	Gayton / East Anglia, UK	1.57	7.9	16	950	0.89	Hartfree et al / 1993
Loamy sand	East Anglia / East An-glia, UK	1.68	7.8	25	1500	0.97	Hartfree et al / 1993
Loamy sand	Kenny Hill / East Anglia, UK	2.96	7.9	32	1100	0.93	Hartfree et al / 1993
Sand	Lilly Field / Surrey, UK	0.29	5.5	12	4100	0.94	Hartfree et al / 1993
Silty clay loam	Nebo / Wiltshire, UK	1.62	4.9	140	8500	0.95	Hartfree et al / 1993
Sandy loam	Salmonds Bridge / West Sussex, UK	1.92	4.7	40	2100	0.91	Hartfree et al / 1993
Sandy loam	Kagoshima / Kagoshima, JP	1.7	5.8	22.0	1310	0.96	Winwick / 2000
Loam	Kochi / Kochi, JP	1.4	5.6	27.6	1990	0.96	Winwick / 2000
Loam	Tsukuba / Ibaraki, JP	3.6	6.5	26.5	737	0.96	Winwick / 2000
Sandy loam	Ushiku / Ibaraki, JP	1.7	5.9	22.1	1270	0.97	Winwick / 2000
Arithmetic mean / Median					2356 / 1405	0.944 / 0.955