Desmedipham

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:

2011-07-05 to 2012-12-13

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)

Qualifier:

according to guideline

Guideline:

other: US EPA Fate, Transport and Transformation Test Guidelines, OPPTS 835.1230, Adsorption/Desorption (Batch Equilibrium),

Version / remarks:

2008

Qualifier:

according to guideline

Guideline:

other: Canada PMRA, Guidelines for Registration of Pesticides, Environmental Chemistry and Fate,

Version / remarks:

1987

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

The test material is [14C-UL-aniline] desmedipham.

Radiolabelling:

yes

Test temperature:

20 °C

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Desmedipham was applied at nominal concentrations of 1.0, 0.3, 0.1, 0.03 and 0.01 mg/L in aqueous 0.01 M CaCl2 solution.
- Sample storage before analysis: The samples of the preliminary and the definitive tests were analyzed immediately after preparation or sampling. Therefore, no storage stability investigations were necessary for these samples.

Matrix no.:

#1

Matrix type:

sandy loam

% Clay:

9

% Silt:

16

% Sand:

75

% Org. carbon:

1.9

pH:

5.7

CEC:

9.8 meq/100 g soil d.w.

Bulk density (g/cm³):

1.24

Matrix no.:

#2

Matrix type:

silt loam

% Clay:

17

% Silt:

60

% Sand:

23

% Org. carbon:

1.8

pH:

6.1

CEC:

11.8 meq/100 g soil d.w.

Bulk density (g/cm³):

1.09

Matrix no.:

#3

Matrix type:

silt loam

% Clay:

17

% Silt:

56

% Sand:

27

% Org. carbon:

2.8

pH:

5

CEC:

10.1 meq/100 g soil d.w.

Bulk density (g/cm³):

1.04

Matrix no.:

#4

Matrix type:

clay loam

% Clay:

31

% Silt:

42

% Sand:

27

% Org. carbon:

5

pH:

7.2

CEC:

22 meq/100 g soil d.w.

Bulk density (g/cm³):

1

Matrix no.:

#5

Matrix type:

sandy loam

% Clay:

15

% Silt:

30

% Sand:

55

% Org. carbon:

2.1

pH:

5

CEC:

11 meq/100 g soil d.w.

Bulk density (g/cm³):

1.13

Details on matrix:

COLLECTION AND STORAGE
- Geographic location: Monheim, Blankenheim & Burscheid
- Sampling depth (cm): 0-20 cm.
- Storage conditions: Refrigerated at = 8 °C.
- Storage length: For a maximum period of 1 month before study start.
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): The soils were sampled, sieved to a particle size of 2 mm.

Soil #1: Laacher Hof AXXa (AX, sandy loam)
Soil #2: Hoefchen am Hohenseh (HF, silt loam)
Soil #3: Hanscheiderhof (HN, silt loam)
Soil #4: Dollendorf II (DD, loam)
Soil #5: Laacher Hof Wurmwiese (WW, sandy loam)

Details on test conditions:

TEST CONDITIONS
- other: For the preliminary tests and for the definitive test the same equipment and experimental set-up was used. Important parameters for the test, i.e. on stability of the test item, adsorption to material of used vessel, soil-to- solution ratio and equilibration time for adsorption and desorption were determined in preliminary tests prior to the definitive test.

TEST SYSTEM
- Type, size and further details on reaction vessel: The tests were performed in centrifuge tubes with screw cap (Teflon, volume 42 mL) in duplicate. The test systems were pre-equilibrated for at least 24 hours by agitation on an overhead shaker at controlled temperature in the dark. After pre-equilibration 20 µL of the respective application solution were added to each test system.

- Amount of soil and solution per treatment: The designated amount of soil (dry weight) was weighed into the centrifuge tubes and aqueous 0.01 M CaCl2 solution was added to obtain a total solution volume of 20 mL, taking into account the residual soil moisture. For a preliminary test, aqueous 0.01 M CaCl2 containing approx. 50 mg/L HgCl2 was used (HgCl2 was only used in preliminary test).

- Soil-solution ratio: Soil-to-solution ratios of 1/40 (0.5 g soil dry weight / 20 mL solution) for all five soils were used in the preliminary tests for determination of the adequate equilibration time and the parental mass balance, as well as for the definitive test. A soil-to-solution ratio of 1/40 was regarded adequate for all soils. Using these soil-to- solution ratios the amount of test item adsorbed to soil was between 44.0 to 58.3% AR.

- Number of reaction vessels/concentration: The adsorption/desorption measurements were performed with five concentrations (0.01 to 1.1 mg/L) covering two orders of magnitude.

Sample No.:

#1

Duration:

24 h

Temp.:

20 °C

Sample No.:

#2

Duration:

8 h

Temp.:

20 °C

Sample No.:

#3

Duration:

24 h

Temp.:

20 °C

Sample No.:

#4

Duration:

4 h

Temp.:

20 °C

Sample No.:

#5

Duration:

24 h

Temp.:

20 °C

Sample no.:

#1

Duration:

24 h

Temp.:

20 °C

Sample no.:

#3

Duration:

24 h

Temp.:

20 °C

Sample no.:

#5

Duration:

24 h

Temp.:

20 °C

Key result

Type:

Koc

Remarks:

Geometric mean (5 soils)

Value:

3 894.1 L/kg

Temp.:

20 °C

Sample No.:

#1

Type:

Koc

Value:

5 236.3 L/kg

Temp.:

20 °C

Matrix:

Soil AX

Sample No.:

#1

Type:

other: 1/n

Value:

0.824 dimensionless

Temp.:

20 °C

Matrix:

Soil AX

Sample No.:

#2

Type:

Koc

Value:

4 299.6 L/kg

Temp.:

20 °C

Matrix:

Soil HF

Sample No.:

#2

Type:

other: 1/n

Value:

0.818 dimensionless

Temp.:

20 °C

Matrix:

Soil HF

Sample No.:

#3

Type:

Koc

Value:

5 034.5 L/kg

Temp.:

20 °C

Matrix:

Soil HN

Sample No.:

#3

Type:

other: 1/n

Value:

0.829 dimensionless

Temp.:

20 °C

Matrix:

Soil HN

Sample No.:

#5

Type:

Koc

Value:

4 138.9 L/kg

Temp.:

20 °C

Matrix:

Soil WW

Sample No.:

#5

Type:

other: 1/n

Value:

0.849 dimensionless

Temp.:

20 °C

Matrix:

Soil WW

Sample No.:

#4

Type:

Koc

Value:

1 908.7 L/kg

Temp.:

20 °C

Matrix:

Soil DD

Sample No.:

#4

Type:

other: 1/n

Value:

0.869 dimensionless

Temp.:

20 °C

Matrix:

Soil DD

Sample No.:

#1

Type:

other: KF

Value:

99.49 L/kg

Temp.:

20 °C

Matrix:

Soil AX

Sample No.:

#2

Type:

other: KF

Value:

77.39 L/kg

Temp.:

20 °C

Matrix:

Soil HF

Sample No.:

#3

Type:

other: KF

Value:

140.97 L/kg

Temp.:

20 °C

Matrix:

Soil HN

Sample No.:

#5

Type:

other: KF

Value:

86.92 L/kg

Temp.:

20 °C

Matrix:

Soil WW

Sample No.:

#4

Type:

other: KF

Value:

95.44 L/kg

Temp.:

20 °C

Matrix:

Soil DD

Adsorption and desorption constants:

Please see Table 4 below

Recovery of test material:

For the test of the adequate adsorption equilibration time a soil-to-solution ratio of 1/40 was used. The final volume after pre-equilibration and application was 20 mL (corrected for soil moisture). After 24 hours the adsorption equilibrium was established for three soils, as the change in test item concentration was less than 5% after this time. Due to the instability of 14C-test item in the soils HF and DD within 24 hours just 8 and 4 hours were chosen as adsorption equilibration time for soils HF and DD, respectively. In sterilised soils, no differences were found within 24 hours. The material balance for all concentrations (individual values) was in the range of 82.7 to 98.8% (Table 3). The mean overall material balance of 92.5% AR found for all test systems demonstrated that no significant radioactivity dissipated from the test vessels or was lost during processing.

Transformation products:

no

Remarks:

No major degradation product was observed.

Details on results (Batch equilibrium method):

PRELIMINARY TEST
- Sample purity:
- Weighed soil: 5, 10 and 20 g (dry weight- Preliminary Soil-to-Solution Ratio Test) & 5, 2 and 0.5 g soil aliquots (dry weight)
- Volume of CaCl2 solution: 20 mL
- Initial test substance concentration: 0.01 mg/L, 0.03 mg/L, 0.10 mg/L, 0.30 mg/L, and 1.13 mg/L (measured)

MAIN TEST: PERFORMANCE
- Test material stability during adsorption/desorption phase: Stability of the test item was confirmed by the determination of the parental mass balance.

OTHER
- Method validation:
Verification of Chromatographic Procedure: In this study the method was used to demonstrate the stability of the test item. The HPLC recovery of this chromatographic method was 105.3% of the injected radioactivity. The instrumental LOD was determined as 5.25 Bq absolute on column, which is equal to a LOD of 1.3% AR. The LOQ was set to three times the LOD, i.e. 0.4% AR. Values between LOD and LOQ are used for calculation just as given. These results demonstrate that this chromatographic method was well suited for analysis of the stability of the test item during the test.

- Findings
- Adsorption measurements:
Desmedipham was stable under the test conditions (parental mass balance: > 88.4% AR). Therefore, the sorption behaviour was calculated based on the radioactivity in the supernatant only. The test was performed using soil- to-solution ratios of 1/40. The equilibration time for adsorption was 4 hours for soil DD, 8 hours for soil HF and 24 hours for soils AX, HN and WW. An overview about the results according to the Freundlich equation is presented in Table 4.

The adsorption behaviour of desmedipham in the concentration range of two orders of magnitude (i.e. from 0.01 to 1.1 mg/L) was accurately described for all soils with the Freundlich equation. The correlation coefficients of the individual isotherms were 0.9974 to 0.9996 (mean: 0.9986). The calculated adsorption constants KF(ads) of the Freundlich isotherms for the five test soils ranged from 77.393 to 140.965 mL/g (mean: 100.040 mL/g) and the calculated Koc(ads) values varied between 1908.7 and 5236.3 mL/g (mean: 4123.6 mL/g). The Freundlich exponents, 1/n were in the range of 0.8177 to 0.8689 (mean: 0.8378).

In the definitive adsorption test 45.7 - 66.8, 37.1 - 60.0, 54.5 - 74.8, 45.8 - 64.5 and 51.7 66.9% AR were adsorbed in soils AX, HF, HN, DD and WW, respectively. The respective concentrations in solution and in soil and the percentage of adsorbed test item are calculated in Table 5.

The pH values of the equilibrium solutions after adsorption varied in the range of pH 5.82 to 7.35 (mean values).


- Desorption measurements:
An overview about the results according to the Freundlich equation is presented in Table 4. One desorption step was performed for each concentration for soils AX, HN and WW. The correlation coefficients of the individual isotherms for the soils AX, HN and WW were 0.9961 to 0.9994 (mean: 0.9978).

After desorption phase, 21.4 - 36.3, 17.9 - 32.1 and 24.9 - 39.1% of the initially adsorbed amount were desorbed in soils AX, HN and WW, respectively. The respective concentrations in solution and in soil and the percentage of desorbed test item are calculated in Table 6.

The calculated desorption constants KF(des) of the Freundlich isotherms for the soils AX, HN and WW ranged from 124.091 to 187.886 mL/g (mean: 154.091 mL/g), the exponents 1/n were in the range of 0.8360 to 0.8606 (mean: 0.8458). The Koc(des) values of the three soils ranged from 5909.1 to 7910.4 mL/g (mean: 6843.2 mL/g). The Koc(des) values were slightly higher (1.3 to 1.5 times higher) than the Koc(ads) values.

Table 3: Recovery of radioactivity after adsorption and desorption, expressed as % AR (measured in duplicates)

Test concentration [mg/L]	Soil
	AX [% of AR]	HF [% of AR]	HN [% of AR]	WW [% of AR]	DD [% of AR]
1.13	91.1	92.5	94.7	91.2	91.0
	87.2	87.4	93.9	91.4	90.8
0.3	96.8	96.8	95.5	92.2	94.7
	96.9	95.6	96.2	96.5	92.4
0.1	98.8	91.1	93.1	95.9	89.1
	95.4	91.1	93.7	96.5	87.4
0.031	89.9	94.2	93.4	95.2	90.0
	92.0	91.8	92.9	92.0	86.9
0.009	94.0	90.1	96.1	96.3	82.7
	92.9	91.0	93.6	92.2	83.4
Mean	93.5	92.2	94.3	93.9	88.8
SD	± 3.4	± 2.6	± 1.2	± 2.2	± 3.6

 

Table 4: Adsorption and desorption constants of desmedipham in soils

Soil Type	Adsorption				Desorption
	KF [mL/g]	1/n	R²	Koc [mL/g]	KF [mL/g]	1/n	R²	Koc [mL/g]
AX	99.490	0.8244	0.9983	5236.3	150.297	0.8360	0.9961	7910.4
HF	77.393	0.8177	0.9974	4299.6	not evaluated ^1
HN	140.965	0.8288	0.9996	5034.5	187.886	0.8407	0.9994	6710.2
WW	86.917	0.8492	0.9988	4138.9	124.091	0.8606	0.9978	5909.1
DD	95.435	0.8689	0.9991	1908.7	not evaluated ^1
Arithmetic Mean	100.040	0.8378	0.9986	4123.6	154.091	0.8458	0.9978	6843.2
Geometric mean				3894.1
Median				4299.6

¹ test item not regarded stable enough in that soil

 

Table 5: Advanced test: Concentration of desmedipham in aqueous and soil phase at the end of the adsorption period (mean) 

Concentration of a.s.	Soil [mg/kg]	Solution [mg/L]	Percentage adsorbed
Soil	Laacher Hof AXXa (Soil ID: AX)
Control	N/A	N/A
0.009 mg/L	250.537	3.115	66.8
0.031 mg/L	789.668	11.514	63.2
0.10 mg/L	2142.813	43.182	55.4
0.30 mg/L	5885.627	150.292	49.5
1.13 mg/L	20665.473	614.770	45.7
Soil	Hoefchen am Hohenseh (Soil ID: HF)
Control	N/A	N/A
0.009 mg/L	224.962	3.754	60.0
0.031 mg/L	684.399	14.146	54.7
0.10 mg/L	1901.381	49.217	49.1
0.30 mg/L	5075.192	170.552	42.7
1.13 mg/L	16795.396	711.522	37.1
Soil	Hanscheiderhof (Soil ID: HN)
Control	N/A	N/A
0.009 mg/L	280.614	2.363	74.8
0.031 mg/L	889.923	9.008	71.2
0.10 mg/L	2570.742	32.483	66.4
0.30 mg/L	7231.509	116.645	60.8
1.13 mg/L	24686.957	514.233	54.5
Soil	Laacher Hof Wurmwiese (Soil ID: WW)
Control	N/A	N/A
0.009 mg/L	242.046	3.327	64.5
0.031 mg/L	754.169	12.402	60.3
0.10 mg/L	2095.652	44.361	54.2
0.30 mg/L	5978.312	147.974	50.2
1.13 mg/L	20728.900	613.184	45.8
Soil	Dollendorf II (Soil ID: DD)
Control	N/A	N/A
0.009 mg/L	251.049	3.102	66.9
0.031 mg/L	801.944	11.207	64.1
0.10 mg/L	2319.488	38.765	59.9
0.30 mg/L	6471.407	135.647	54.4

  

Table 6: dvanced test: Concentration of desmedipham in aqueous and soil phase at the end of the desorption period (mean)

Concentration of a.s.	Soil [mg/kg]	Solution [mg/L]	Percentage adsorbed
Soil	Laacher Hof AXXa (Soil ID: AX)
Control	N/A	N/A
0.009 mg/L	196.906	1.341	21.4
0.031 mg/L	594.441	4.881	24.7
0.10 mg/L	1475.011	16.695	31.2
0.30 mg/L	3749.976	53.391	36.3
1.13 mg/L	13214.884	186.265	36.1
Soil	Hanscheiderhof (Soil ID: HN)
Control	N/A	N/A
0.009 mg/L	230.459	1.254	17.9
0.031 mg/L	701.607	4.708	21.2
0.10 mg/L	1917.734	16.325	25.4
0.30 mg/L	5086.401	53.628	29.7
1.13 mg/L	16767.737	197.980	32.1
Soil	Laacher Hof Wurmwiese (Soil ID: WW)
Control	N/A	N/A
0.009 mg/L	181.759	1.507	24.9
0.031 mg/L	537.802	5.409	28.7
0.10 mg/L	1386.169	17.737	33.9
0.30 mg/L	3782.353	54.899	36.8
1.13 mg/L	12625.327	202.589	39.1

 

Validity criteria fulfilled:

yes

Conclusions:

RMS comments and conclusion: The study was performed in line with OECD 106 (2002). The amount of soil in the tested soils differed in respect to pH (5.0-7.2), orgC (1.8-5.0 %) and clay content (9-31 %). Mass balances were within the range of 88.8 to 94.3 % of AR in soils. In control samples without soil the test item did not adsorb to the surface of the test vessels. In four soils the test item was stable during the study period. HgCl2 was only used in preliminary study. The parental mass balance for the adsorption/desorption phase was > 92.2% AR (just 88.8% AR in soil DD where some hydrolytic degradation occurred due to its higher pH). No major degradation product was observed. The study is considered valid. The adsorption constants KF(ads) of desmedipham for the five test soils calculated based on the Freundlich isotherms ranged from 77.393 to 140.965 mL/g (mean: 100.040 mL/g). The respective Koc(ads) values were in the range of 1908.7 and 5236.3 mL/g (mean: 4123.6 mL/g) and will be used in the risk assessment. The mobility of desmedipham in soil based on KF and/or Koc values can be classified as immobile for adsorption and desorption. After re-evaluation, the study is still considered valid.

Executive summary:

The adsorption/desorption behaviour of [14C-UL-aniline] desmedipham was studied in the five different German soils: Laacher Hof AXXa (AX, sandy loam), Hoefchen am Hohenseh (HF, silt loam), Hanscheiderhof (HN, silt loam), Dollendorf II (DD, loam) and Laacher Hof Wurmwiese (WW, sandy loam) using the batch equilibrium method.

The adsorption phase of the study was carried out using air-dried soils pre equilibrated in aqueous 0.01 M CaCl2 solution with a soil-to-solution ratio of 1:40. Desmedipham was applied at nominal concentrations of 1.0, 0.3, 0.1, 0.03 and 0.01 mg/L in aqueous 0.01 M CaCl2 solution. The desorption phase for all five soils was performed by supplying pre-adsorbed soil samples with fresh aqueous 0.01 M CaCl2 solution for one desorption cycle. The adsorption phase was carried out for 4 hours for soil DD, 8 hours for soil HF and 24 hours for the other three soils followed by one desorption phase of 24 hours for the soils AX, HN and WW in the dark at 20 ± 2 °C. The aqueous supernatant after adsorption and desorption was separated by centrifugation and the amount of
desmedipham in the supernatants were analysed by liquid scintillation counting (LSC). After desorption, the soils AX, HN and WW were extracted, dried and combusted. The trapped 14CO2 after combustion was measured by LSC. The soils HF and DD were extracted, dried and combusted after adsorption. 

The adsorption parameters were calculated using the Freundlich adsorption isotherm. The test item was sufficient stable throughout the study. Overall mass balances were established during the definitive test by determination of the radioactivity content of the CaCl2 supernatants of the adsorption and desorption phases as well as of the remaining soils using LSC measurements and combustion/LSC, respectively. The recovery of the applied radioactivity for all concentrations and soils was in the range of 88.8 to 94.3% AR (mean: 92.5% AR). The calculated Koc(ads) values varied between 1908.7 and 5236.3 mL/g (mean: 4124 mL/g). The Freundlich exponents 1/n were in the range of 0.8177 to 0.8689 (mean: 0.84). 

Description of key information

The calculated KFoc(ads) values varied between 1908.7 and 5236.3 L/kg (geomean: 3894.1 L/kg). The Freundlich exponents 1/n were in the range of 0.8177 to 0.8689 (mean: 0.8378).

 

In the table below all available studies are listed. For some studies only the results are presented since they are not considered relevant due to the reasons given under “Assessment”. All available studies have been evaluated within the scope of Plant Protection Regulation in the respective Draft Renewal Assessment Report (DAR) under Regulation (EC) 1107/2009.

Test type	Result	Assessment	Reference
OECD 106 batch equilibrium study	KOC range 1908.7 to 5236.3 mL/g. Geomean 3894.1 L/kg	Key study	Hellpointner (2012)
Carried out to OECD 106 guidelines	No result- Rapid hydrolysis observed in study	Not considered to be valid in the DAR. Rapid hydrolysis observed in study.	Mackie (1991)
Carried out to OECD 106 guidelines	No result- Rapid hydrolysis observed in study	Not considered to be valid in the DAR	Bruehl (1994)
Adsorption measured by TLC	Rf ranges given	Not considered to be valid in the DAR	Feyerabend (1989)

Key value for chemical safety assessment

Koc at 20 °C:

3 894.1