Fenamiphos

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:

2015-07-30 to 2015-09-29

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: OPPTS 835.1230 Adsorption/Desorption (Batch Equilibrium)

Version / remarks:

October 2008

Deviations:

no

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

January 2000

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Specific details on test material used for the study:

- Chemical name: Ethyl 3-methyl-4-(methylthio)phenyl (1-methylethyl) phosphoramidate
- CAS number: 22224-92-6

Radiolabelling:

yes

Test temperature:

ambient temperature (20 +/- 2 °C.)

Analytical monitoring:

yes

Details on sampling:

not specified

Matrix no.:

#1

Matrix type:

sandy loam

% Clay:

13

% Silt:

16

% Sand:

71

% Org. carbon:

3.4

pH:

5.1

CEC:

15.1 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

clay

% Clay:

41

% Silt:

36

% Sand:

23

% Org. carbon:

4.3

pH:

7.3

CEC:

35.7 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

loamy sand

% Clay:

6

% Silt:

5

% Sand:

89

% Org. carbon:

1.8

pH:

4.7

CEC:

6.5 meq/100 g soil d.w.

Matrix no.:

#4

Matrix type:

clay loam

% Clay:

22

% Silt:

47

% Sand:

31

% Org. carbon:

4.1

pH:

5.4

CEC:

18.6 meq/100 g soil d.w.

Matrix no.:

#5

Matrix type:

clay loam

% Clay:

26

% Silt:

34

% Sand:

40

% Org. carbon:

1.5

pH:

7.3

CEC:

10.1 meq/100 g soil d.w.

Details on matrix:

Data as given in study report.

Matrix 1: Calke
Grid reference: SK 36030, 21586
Site description: old grass meadow
Sampling method: spade after turf removal
Sampling depth (cm): 10 - 20
Pesticide history: none since 2000
Water content (% dry weight): 12.92

Matrix 2: Empingham
Grid reference: SK 95645, 06847
Site description: old grass meadow
Sampling method: spade after turf removal
Sampling depth (cm): 4 - 10
Pesticide history: None for >10 years
Water content (% dry weight): 20.16

Matrix 3: Ingleby
Grid reference: SK 34636, 26943
Site description: permanent pasture field
Sampling method: spade after turf removal
Sampling depth (cm): 10 - 20
Pesticide history: infrequent spraying to control broadleaf weeds but not normally where samples taken
Water content (% dry weight): 4.40

Matrix 4: Brierlow
Grid reference: SK 09512, 69147
Site description: permanent grassland field
Sampling method: spade after turf removal
Sampling depth (cm): 13 - 23
Pesticide history: none for 12 years
Water content (% dry weight): 34.47

Matrix 5: Valencia
Grid reference: not known
Site description: set aside field
Sampling method: 20 cm soil cores
Sampling depth (cm): 20
Pesticide history: Glyphosate (3 times/year)
Water content (% dry weight): 11.60

Details on test conditions:

TEST SYSTEM
- Type, size and further details on reaction vessel: 30 mL glass centrifuge tubes
- Amount of soil and water per treatment: The equivalent of 10 g oven dry weight of each soil was added to each test vessel. A volume of 0.01 M calcium chloride solution was added to each vessel to result in a total aqueous volume of 10 mL, taking into account the moisture content of the soil.

- Number of reaction vessels/concentration and soil matrix: 11
- Measuring equipment: pH meter, liquid scintillation counters with automatic quench correction, HPLC/UV
- Method of preparation of test solution: Solutions of 14C-fenamiphos in acetonitrile were prepared so that the concentration of organic solvent would be the same in each test vessel and not exceed 0.1% of the aqueous volume. The nominal concentrations of fenamiphos in these treatment solutions were 5.0, 1.5, 0.5, 0.15 and 0.05 mg/mL. The treatment solution for the high fenamiphos concentration (5.0 mg/L) was prepared by radiodilution of a portion of 14C-fenamiphos with non-radiolabelled fenamiphos. The remaining treatment solutions (0.05, 0.15, 0.5 and 1.5 mg/L) were prepared without radiodilution. The concentration of radioactivity in each treatment solution was accurately determined by the radioassay of replicate aliquots. The radiochemical purity of fenamiphos was determined by high performance liquid chromatography prior to application to the soil slurries.

Sample No.:

#1

Remarks:

Please refer to attached supplementary information

Key result

Sample No.:

#1

Type:

Koc

Value:

74.2

Sample No.:

#1

Remarks on result:

other: Please refer to attached supplementary information

Transformation products:

not specified

Details on results (Batch equilibrium method):

The mass balance of radioactivity was measured in one vessel of each soil type treated at the highest Fenamiphos concentration following the adsorption phase. Recoveries of radioactivity were in the range 89.1 – 102.5 % of the amounts applied. Aqueous solutions and soil extracts from vessels treated at the highest fenamiphos concentration were analysed by HPLC. Fenamiphos represented 82.7 – 90.8 % sample radioactivity in the aqueous solution and 81.1 – 94.2% sample radioactivity in soil extracts The Freundlich adsorption coefficients were in the range 0.789 – 3.40 indicating some adsorption of fenamiphos to the test soils. Adsorption coefficients corrected for organic carbon content were in the range 43.8 – 150. Values of the exponent 1/n were in the range 0.85 – 0.99. There was no correlation between soil pH and the degree of adsorption. For desorption mean recoveries were in the range 87.6 – 98.9% of applied radioactivity. For each soil the Freundlich desorption coefficient (in the range 4.2 – 36.0) was higher than the adsorption coefficient, indicating some degree of irreversibility to the adsorption of Fenamiphos.

The mass balance of radioactivity was measured in one vessel of each soil type treated at the highest fenamiphos concentration following the adsorption phase. Recoveries of radioactivity were in the range 89.1–102.5 % of the amounts applied. Aqueous solutions and soil extracts from vessels treated at the highest fenamiphos concentration were analysed by HPLC. Fenamiphos represented 82.7–90.8 % sample radioactivity in the aqueous solution and 81.1–94.2 % sample radioactivity in soil extracts. The mass balance of radioactivity was measured in the two remaining vessels of each soil type treated at the highest fenamiphos concentration following the desorption phase. Mean recoveries were in the range 87.6–98.9 % of applied radioactivity. Aqueous solutions and soil extracts from vessels treated at the highest fenamiphos concentration were analysed by HPLC. Fenamiphos represented 66.6–85.9 % sample radioactivity in the aqueous solution and 80.7–95.4% sample radioactivity in soil extracts.

Table 1: Recovery of radioactivity after adsorption at an initial fenamiphos concentration of 5.0 mg/L

	Calke	Empingham	Ingleby	Brierlow	Valencia
Adsorption solution	9.0	10.0	39.1	7.4	17.5
Soil extracts	76.4	74.7	58.8	80.8	72.6
Non-extractable	6.2	4.4	4.6	6.0	2.5
Total recovery	91.6	89.1	102.5	94.2	92.6

Results are expressed as % applied radioactivity and are from a single replicate.

 

Table 2: Recovery of radioactivity after adsorption and desorption at an initial fenamiphos concentration of 5.0 mg/L

	Calke	Empingham	Ingleby	Brierlow	Valencia
Adsorption solution	11.8	13.0	29.1	6.8	19.1
Desorption solution	8.1	4.3	8.8	2.2	4.1
Soil extracts^a	69.2	70.4	47.0	73.7	69.4
Non-extractable^a	7.0	3.9	2.7	11.9	6.3
Total recovery	96.1	91.6	87.6	94.6	98.9

Results are expressed as % applied radioactivity and are the means of two replicates. The results for adsorption and desorption solution include only the solution separated from soil after centrifugation.
^a After desorption

 

The Freundlich adsorption coefficients were in the range 0.789–3.40 indicating some adsorption of fenamiphos to the test soils. Adsorption coefficients corrected for organic carbon content were in the range 43.8–150. Values of the exponent 1/n were in the range 0.85–0.99. There was no correlation between soil pH and the degree of adsorption. The Freundlich desorption coefficients were in the range 4.2–36.0. The latter were higher than the adsorption coefficients in all soils, indicating some degree of irreversibility to the adsorption of fenamiphos (Table CA 7.1.3.1.1/03-4).

 

Table 3: Adsorption and desorption characteristics of Fenamiphos

	Organic carbon content (%)	Adsorption			Desorption
		Freundlich adsorption distribution coefficient	Coefficient of adsorption per unit organic carbon	1/n	Freundlich desorption distribution coefficient	Coefficient of desorption per unit organic carbon	1/n
Calke	3.4	2.01	59.1	0.88	4.20	124	0.96
Empingham	4.3	3.01	70.0	0.94	6.23	145	0.88
Ingleby	1.8	0.789	43.8	0.85	4.98	277	1.20
Brierlow	4.1	3.40	82.9	0.99	36.0	878	1.50
Valencia	1.5	2.25	150	0.89	12.1	807	1.12

1/n    Exponent of the Freundlich adsorption or desorption isotherm

Refer to OECD 106 for definition of coefficient units

Validity criteria fulfilled:

yes

Conclusions:

Freundlich adsorption coefficients for Fenamiphos were in the range 0.789–3.40 and adsorption coefficients corrected for organic carbon content were in the range 43.8–150. There was no correlation between soil pH and the degree of adsorption. For each soil the desorption coefficient was higher than the adsorption coefficient, indicating some degree of irreversibility to the adsorption of Fenamiphos.

Executive summary:

The sorption properties of fenamiphos were studied in five soils using the batch equilibrium method in accordance with OECD TG 106 and US EPA OPPTS 835.1230. The test soils included a range of textural classes, with pH values (in CaCl₂) in the range 4.7–7.3 and organic carbon contents in the range 1.5%-4.3%. Fenamiphos radiolabelled with carbon-14 in the benzene ring was used. HPLC analysis of selected samples in the preliminary studies indicated that fenamiphos was unstable in both aqueous solution and in soil. Therefore, an adsorption equilibration time of 1 hour was chosen for the main experiment. Soil samples were then desorbed once with fresh calcium chloride solution for 1 hour. Concentrations of radioactivity in solution were measured directly and, from these, the concentration of radioactivity in the soil was determined. Both values were corrected for actual proportions of fenamiphos present in solution and soil exacts, as determined by chromatographic analysis. Freundlich adsorption coefficients for fenamiphos were in the range 0.789–3.40 and adsorption coefficients corrected for organic carbon content were in the range 43.8–150. There was no correlation between soil pH and the degree of adsorption. For each soil the desorption coefficient was higher than the adsorption coefficient, indicating some degree of irreversibility to the adsorption of fenamiphos.

Description of key information

Freundlich adsorption coefficients for the test item were in the range 0.789 – 3.40 and adsorption coefficients corrected for organic carbon content were in the range 43.8 – 150. There was no correlation between soil pH and the degree of adsorption. For each soil the desorption coefficient was higher than the adsorption coefficient, indicating some degree of irreversibility to the adsorption of the test substance. In compliance with the Renewal Assessment Report prepared according to Regulation (EC) N0 1107/2009, Volume 3 – B.8 (CP) (June 2018) and the List of Endpoints from EFSA Conclusion on fenamiphos, a Koc value of 106.6 mL/g is considered for the exposure assessment according to Regulation (EC) No 1907/2006 (REACH).

Key value for chemical safety assessment

Koc at 20 °C:

106.6

Additional information

Experimental data on the adsorption/desorption behaviour of  Fenamiphos is available.  Two adsorption/desorption studies of Hein (2000) and Simon (1990) were evaluated in the PPP Draft Assessment Report (DAR) (Vol. 3, Annex B, Point 8.2.1, November 2003). Whilst endpoints for risk assessment were derived from these studies a number of deficiencies highlighted were noted in the evaluations presented in the DAR by the RMS. Furthermore the Simon (1990) study was non-GLP, non-guideline compliant. This study is hence disregarded. The Hein (2000) study was still taken into consideration for deriving the geometric mean Koc value in the EFSA Final conclusion - Appendix X, List of Endpoints. However, a new guideline, GLP compliant study has been carried out (Button) and is presented below. The study was In the original fenamiphos dossier was submitted with the EU Plant Protection Produt (PPP) Renewal Dossier for Fenamiphos (June 2018).

 

Key information - Button, 2015

The sorption properties of fenamiphos were studied in five soils using the batch equilibrium method in accordance with OECD TG 106 and US EPA OPPTS 835.1230 (Button, 2015). The test soils included a range of textural classes, with pH values (in CaCl₂) in the range 4.7 – 7.3 and organic carbon contents in the range 1.5% - 4.3%. Fenamiphos radiolabelled with carbon-14 in the benzene ring was used. HPLC analysis of selected samples in the preliminary studies indicated that fenamiphos was unstable in both aqueous solution and in soil. Therefore, an adsorption equilibration time of 1 hour was chosen for the main experiment. Soil samples were then desorbed once with fresh calcium chloride solution for 1 hour. Concentrations of radioactivity in solution were measured directly and, from these, the concentration of radioactivity in the soil was determined. Both values were corrected for actual proportions of fenamiphos present in solution and soil exacts, as determined by chromatographic analysis. Freundlich adsorption coefficients for fenamiphos were in the range 0.789 – 3.40 and adsorption coefficients corrected for organic carbon content were in the range 43.8 – 150. There was no correlation between soil pH and the degree of adsorption. For each soil the desorption coefficient was higher than the adsorption coefficient, indicating some degree of irreversibility to the adsorption of fenamiphos. In compliance with the Renewal Assessment Report prepared according to Regulation (EC) N0 1107/2009, Volume 3 – B.8 (CP) (June 2018) and the List of Endpoints from EFSA Conclusion on fenamiphos, a Koc value of 106.6 mL/g is considered for the exposure assessment according to Regulation (EC) No 1907/2006 (REACH). A data matrix is given below.

 

Soil	Soil Class	pH (CaCl2)	% Organic Carbon	KF (mL/g)	KFoc (mL/g)	1/n
Calke (Button, 2015)	Sandy loam	5.1	3.4	2.01	59.1	0.88
Empingham (Button, 2015)	Clay	7.3	4.3	3.01	70.0	0.94
Ingleby (Button, 2015)	Sand	4.7	1.8	0.789	43.8	0.85
Brierlow (Button, 2015)	Clay loam	5.4	4.1	3.40	82.9	0.99
Valencia (Button, 2015)	Clay loam	7.3	1.5	2.25	150	0.89
Sanger (Hein, 2000)	Loamy sand	6.3	0.57	1.37	240.9	0.90
T&G Groves (Hein, 2000)	Sand	6.26	0.53	1.10	207.2	0.95
Byromville (Hein, 2000)	Loamy sand	5.57	0.63	0.93	147.9	0.95
Arithmetic mean					-	0.92
Geometric mean					106.6	-

No pH dependence was found. Modelling input parameters are in bold.

 

Supporting information - Hein, 2000

The adsorption and desorption of [phenyl-1-¹⁴C]-fenamiphos (¹⁴C-770B, radiochemical purity >98%) were determined in four soils according to US EPA and OECD guidelines. Soils were air dried and sieved (2 mm mesh). Several preliminary tests were performed (including determination of HPLC detection limit, adsorption to the test vessels, stability of the test substance and the soil/solution ratio, adding biocide HgCl₂). Because the preliminary tests showed degradation processes taking place within 6 hours, the authors decided to conduct the definitive test using equilibration times of 1 hour for adsorption and 1 hour for desorption. For the adsorption and desorption measurements, four nominal test concentrations were prepared in distilled 0.01 M CaCl₂ solutions (5.00; 0.50; 0.05 and 0.01 mg/L). Twelve grams of dried soil were weighed into borosilicate glass tubes with Teflon screw caps and 20 mL of one of the test concentrations was added. Each concentration level was tested in duplicate. After the determined shaking period (1 h), the tubes were centrifuged and the supernatant completely decanted. Two aliquots of 1 mL were taken for LSC analyses. In addition, the highest test concentration was analysed by HPLC (LOD 140.13 dpm/100 μL).

Following the decantation of the adsorption phase, 20 mL of CaCl₂ solution were added to each tube. The tubes were shaken for 1h and handled as described above. The soil was mixed with 0.4 g cellulose/g soil and the soil bound residue was determined by combustion followed by LSC. Results HPLC analyses showed that the recovery of [phenyl-1-¹⁴C]-fenamiphos in the aqueous phase after 6 hours of adsorption was 81.6, 87.2, 93.4 and 89.3% of AR (applied radioactivity) for loamy sand 1, sand, sandy loam and loamy sand 2, respectively and decreased to 60.8, 72.2, 85.3 and 71.1% after 72 hours of adsorption. The total radioactivity in the aqueous phase did not change significantly. The total amount of AR recovered from 16 samples ranged from 99.9 to 109.9%. Koc values calculated by the author were 240.9, 207.2, 468.9, 147.9 for loamy sand (1), sand, sandy loam and loamy sand (2), respectively and Kd values 1.37, 1.10, 0.70 and 0.93 L/kg.

No sufficient information or the parameters of the soils were not within the set criteria by the OECD 106 guideline, thus, several of the tested soils were not consiedere as relevant for risk assessment. The following soils, were still regarding for the geometric mean Koc value - Sanger soil, T&G Groves soil and Byromville soil. The Koc values scientifically valid have been calculated for loamy sand (240.9 L/kg), sand (207.2 L/kg) and loamy sand soil (147.9 L/kg) and should be considered for risk assessment.

 

Conclusion

Based on the most reliable information (Button, 2015) the Freundlich adsorption coefficients for Fenamiphos are considered in the range 0.789 – 3.40 and adsorption coefficients corrected for organic carbon content are considered in the range 43.8 – 150. In the study of Buton (2015) no correlation between soil pH and the degree of adsorption was observed. For each soil the desorption coefficient was higher than the adsorption coefficient, indicating some degree of irreversibility to the adsorption of Fenamiphos. In compliance with the Renewal Assessment Report prepared according to Regulation (EC) N0 1107/2009, Volume 3 – B.8 (CP) (June 2018) and the List of Endpoints from EFSA Conclusion on fenamiphos, a Koc value of 106.6 mL/g is considered for the exposure assessment according to Regulation (EC) No 1907/2006 (REACH).