pymetrozine (ISO); (E)-4,5-dihydro-6-methyl-4-(3-pyridylmethyleneamino)-1,2,4-triazin-3(2H)-one

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:

weight of evidence

Study period:

03 Sep 1992 to 17 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)

Version / remarks:

May 1981

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Pesticide Assessment Guidelines, Subdivision N, Chemistry: Environmental Fate, Section 163-1: Leaching and Adsorption/Desorption Studies

Version / remarks:

October 1982

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Environmental Chemistry and Fate, Guidelines for Registration of Pesticides in Canada", Section B: Mobility, 1: Adsorption-Desorption Measurements

Version / remarks:

July 1987

Deviations:

no

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Remarks:

[14C]-labelled at position 6 of the triazine ring

Test temperature:

The study was performed at 20 °C (± 1 °C).

Analytical monitoring:

yes

Details on sampling:

- Sample preparation for analysis: The supernatant solution of sample 6' obtained at adsorption equilibrium (about 45 mL) was concentrated at 40°C and 50 mbar to 2.0 mL using a vacuum rotatory evaporator, passed through a 0.45 μm filter, their radioactivity determined by LSC and aliquots submitted to analysis by HPLC. The recoveries ranged from 89 to 96%.
- Organic soil extracts: The combined methanol extracts from soil of samples 6' were concentrated at 30°C and 200 mbar to a volume of 5 mL using a vacuum rotatory evaporator, passed through a 0.45 μm filter, their radioactivity determined by LSC and the aliquots submitted to HPLC analysis. The recoveries ranged from 93 to 95%.
- Soils: The extracted soils were air-dried and thereafter their residual radioactivity determined by combustion of duplicate samples.

Details on matrix:

- Soil preparation: The soils were air-dried at room temperature and passed through a 1 mm sieve.
Detailed soil characteristics are presented in 'Any other information on materials and methods incl. tables'

Details on test conditions:

TEST SYSTEM
- Test vessels: The adsorption and desorption experiments were conducted in 150 mL centrifuge tubes, which were shaken in a temperature controlled water bath in the dark at 250 strokes per minute.
- Amount of soil: 10 ± 1 g for all soils (dry weight basis).
- Aqueous phase: 50 mL of 0.01 mol CaCl2 solution.
- Concentrations: The test substance was applied at 5 concentrations ranging between about 0.2 and 4.0 μg/mL (0.2, 0.4, 1.0, 2.0 and 4.0 µg/mL). In addition one untreated control sample (vehicle only) was set up.
- Equilibration time: The time for reaching an equilibrium for the adsorption of the test substance was proven in a pre-test. For adsorption, the samples were shaken for 6 hours.
- Experimental set-up: For each soil type, eight tarred test tubes containing 10 ± 1 g soil on dry weight basis were prepared. The highest concentration was performed in triplicate. One was used for analysis of parent compound and possible degradates/ impurities in the aqueous phase and in soil sediment after the adsorption step. The second was used as reserve sample.

TEST SUBSTANCE PREPARATION
Prior to the preparations of the application solutions, the total amount of the radiolabelled test substance (about 1 mg) was dissolved in accurately 50 mL of Water (nanopur) and deluted with exactly 5.3 mg unlabelled test substance. Thereafter, the amount of radioactive material present was determined by LSC (Liquid Scintillation Counting) to be 6.15 mg with a specific activity of 0.29 MBq/mg. A volume of 41.4 mL of this solution was transferred into a 50 mL volumetric flask and adjusted with 0.01 mol CaCl2 (stock solution). For this purpose, appropriate aliquots of the stock solution were transferred into volumetric flasks and diluted with 0.01 mol CaClz to the intended concentrations. The activity of these solutions was checked by LSC.

TEST SUBSTANCE ADDITTION
For each soil, 10 ± 1 g of air-dry material was weighed into tarred centrifuge tubes and suspended with 25 mL of 0.01 mol CaCl2-solution. Portions of 25 mL of the treatment solutions were added to the test vessels resulting in initial test concentrations between 0 (blank) and about 4 μg/mL. Finally, the total weight was determined.

CONDUCT OF THE ADSORPTION/DESORPTION EXPERIMENTS
The centrifuge tubes were shaken at 20°C for 6 hours in the darkness. The soils and the solutions were then separated by centrifugation at 2000 rpm for 30 minutes (depending on the sedimentation behavior of the soils). Directly from the clear supernatant 2 aliquots of 0.1 mL each were taken, mixed with 10 mL of scintillation solution (Irgascint A300) and submitted to liquid scintillation counting. Then the remaining supernatants were cautiously removed and the centrifuge tubes still containing the wet soil were weighed again. Thereafter, 50 mL of the CaCl2-solution were added to the wet soil containing the adsorbed a.i., the weight was determined and the test tubes were shaken for 16 hours at 20°C in the darkness (first desorption step). After completion of this first desorption step the solutions and soils were again separated by centrifugation. Two aliquots of supernatant were radioassayed and the test vessels were re-weighed and the desorption procedure was repeated once for 6 hours in the darkness (desorption step 2).

MASS BALANCE ANALYSIS
For all samples a mass balance was established.
- Samples 1-6: After completion of the adsorption and desorption steps, the radioactivity in the residual soil sediment was determined by combustion. The radioactivity remaining adsorbed to the incubation tube was dissolved in 25 mL methanol. Thereafter, a balance was established comprising the radioactivity found in adsorption, desorption solutions, soil sediment after combustion and in washings of the test tubes (radioactivity adsorbed to glass-walls). Figures were expressed in % of the radioactivity initially applied.
- Samples 6’: Sample 6' was worked-up directly after the adsorption step. After removal of the aqueous phase, its radioactivity was determined. The remaining sediment was then submitted to exhaustive extraction with methanol. For this purpose, the sediment was three times extracted with 50 mL methanol by shaking at room temperature for 20 min. at 300 rpm followed by centrifugation at 2000 rpm for 30 min. The radioactivity in extracts and in the final sediment was determined by LSC and combustion, respectively. Finally, the test tubes were carefully washed with methanol.

A balance was given comprising the radioactivity found in soil sediment (extractables and non-extractables), in the aqueous phase and in the washings of test tubes. Values are given in % of the radioactivity initially applied. Aqueous phase and organic extracts were further analyzed.

Sample No.:

#1

Duration:

6 h

Initial conc. measured:

>= 0.2 - <= 4 mg/kg soil d.w.

pH:

7

Temp.:

20 °C

Remarks:

Four concentrations were used: 0.2, 0.4, 1.0, 2.0 and 4.0 µg/mL

Sample No.:

#2

Duration:

6 h

Initial conc. measured:

>= 0.2 - <= 4 mg/kg soil d.w.

pH:

5.7

Temp.:

20 °C

Remarks:

Four concentrations were used: 0.2, 0.4, 1.0, 2.0 and 4.0 µg/mL

Sample No.:

#3

Duration:

6 h

Initial conc. measured:

>= 0.2 - <= 4 mg/kg soil d.w.

pH:

5.7

Temp.:

20 °C

Remarks:

Four concentrations were used: 0.2, 0.4, 1.0, 2.0 and 4.0 µg/mL

Sample No.:

#4

Duration:

6 h

Initial conc. measured:

>= 0.2 - <= 4 mg/kg soil d.w.

pH:

7.1

Temp.:

20 °C

Remarks:

Four concentrations were used: 0.2, 0.4, 1.0, 2.0 and 4.0 µg/mL

Sample No.:

#5

Duration:

6 h

Initial conc. measured:

>= 0.2 - <= 4 mg/kg soil d.w.

pH:

6.6

Temp.:

20 °C

Remarks:

Four concentrations were used: 0.2, 0.4, 1.0, 2.0 and 4.0 µg/mL

Key result

Sample No.:

#1

Type:

other: freundlich Koc

Value:

402 L/kg

pH:

7

Temp.:

20 °C

Matrix:

Loamy sand (Collombey)

% Org. carbon:

0.76

Key result

Sample No.:

#2

Type:

other: freundlich Koc

Value:

1 291 L/kg

pH:

5.7

Temp.:

20 °C

Matrix:

Sand (Lakeland)

% Org. carbon:

0.43

Key result

Sample No.:

#3

Type:

other: freundlich Koc

Value:

518 L/kg

pH:

5.7

Temp.:

20 °C

Matrix:

Silt loam (Les Evouettes)

% Org. carbon:

1.39

Key result

Sample No.:

#4

Type:

other: freundlich Koc

Value:

307 L/kg

pH:

7.1

Temp.:

20 °C

Matrix:

Silt loam (Vetroz)

% Org. carbon:

4.39

Key result

Sample No.:

#5

Type:

other: freundlich Koc

Value:

246 L/kg

pH:

6.6

Temp.:

20 °C

Matrix:

Humic soil (Illarsaz)

% Org. carbon:

19.34

Adsorption and desorption constants:

An overview of all adsorption and desorption coefficients is provided in 'Any other information on results incl. tables'.

Recovery of test material:

The distribution pattern of 14C-activity and the total recovery for each soil type and sample are presented in 'Any other information on results incl. tables'.

- Samples 2 - 6: The total recovery ranged, on the average, between 96 and 102% of the radioactivity applied. The amount of radioactivity found to be adsorbed to soil particles ranged, on the average, from 9.1 (Collombey Loamy sand) to 78.4% (Illarsaz humic soil) of the dose applied. The amount of radioactivity found in the aqueous phases of soil Collombey was, on the average, 69.3, 16.9 and 6.5% for the adsorption step, desorption step 1 and desorption step 2, respectively. The corresponding figures for soil Illarsaz were 9.0, 4.6 and 3. 7%. Only negligible amounts of radioactivity were found to be adsorbed to glass-walls ranging, on the average, between 0.6 and 1.1 % of the radioactivity applied.
- Samples 6': Total recoveries of these samples worked-up after the adsorption step ranged from 94 to 96% of the dose applied. In supernatant aqueous phases, extractables of soil sediment, residual soil and washings of glass-wares the range of radioactivity was 6.6 - 64.1, 26.8 - 63.3, 2.8 - 25.3 and 0.04 - 0.43 %, respectively.

Concentration of test substance at end of adsorption equilibration period:

The adsorption results are presented in ‘any other information on results incl. tables’. The adsorption constants k were in the range between 3.1 μg/g of soil Collombey and 47.7 μg/g of soil for the humic soil (Illarsaz). These results demonstrate a strong adsorption of the test substance onto soil particles. The slopes 1/n for the adsorption isotherms ranged between 0. 79 to 0.95, indicating that the Freundlich adsorption isotherms would not strongly follow the distribution law. When related to the organic carbon content (koc) or to the organic matter content (Q-value) figures ranging from 246 to 1291 μg/g of organic carbon and from 143 to 7 49 μg/g organic matter were found. On the average, the corresponding values were 503 and 292 μg/g of organic carbon and organic matter, respectively. These data classify the test substance as a strongly adsorbed pesticide.

Concentration of test substance at end of desorption equilibration period:

The desorption results are presented in ‘Any other information on results incl. tables’. Desorption constants of the first desorption step ranged from 6.2 to 64.0 μg/g of soil and for the second desorption step from 15.2 to 70.0 μg/g of soil. When compared with the adsorption values they were significantly higher, indicating a partial irreversibility of the adsorption of the test substance.

Remarks on result:

other: see 'Any other information on results incl. tables'.

Remarks on result:

other: see 'Any other information on results incl. tables'.

Transformation products:

yes

Remarks:

Transformation products were detected but not identified. See 'Details on results (Batch equilibrium method)'

Details on results (Batch equilibrium method):

ANALYSIS OF RADIOACTIVITY
The supernatant solution obtained after adsorption of the radiolabelled test substance and the extractable radioactivity of samples 6' were analyzed by HPLC. The proportion of the solution radioactivity associated with the test substance ranged from 77.4 to 87.9% in Illarsaz and Vetroz soils, respectively. Besides the parent compound, impurities 2 and 3 and the metabolite fraction 4 were found, indicating a slight degradation of the test substance during the adsorption equilibrium. These fractions and impurities were not further identified. Analysis of extractable radioactivity from soils showed that exclusively the parent compound was present. Due to their higher polarity, impurities 2 and 3 and the metabolite fraction 4 were much less adsorbed than the test substance and were therefore present in a much higher proportion in the aqueous supernatants. Therefore, in order to correctly calculate the adsorption isotherms, the solution concentrations of the test substance, calculated from the radioactivity measurements and the HPLC determinations of the proportion of the test substance present, were used rather than just the radioactivity concentrations.

Table:Balance of Radioactivity with Soil Collombey after Adsorption and Desorption (Values given in% of the Radioactivity applied)

Sample Number	Soil Ads	Aqueous Phase			Glassware*	Extractable	Non- extractable	Recovery
		Ads	Des 1	Des 2
2	11.4	70.8	15.8	8.0	0.99			106.9
3	11.0	65.0	18.3	7.0	0.59			101.9
4	9.2	68.2	16.1	6.6	0.64			100.7
5	7.2	70.4	17.3	5.7	0.58			101.3
6	6.6	72.0	16.7	5.1	0.58			101.0
Average	9.1	69.3	16.8	6.5	0.68			102.4
6'		64.1			0.04	26.8	2.8	93.7

* Radioactivity adsorbed to glass-wall of incubation tubes finally removed by extraction with methanol.

Table:Balance of Radioactivity with Soil Lakeland after Adsorption and Desorption (Values given in% of the Radioactivity applied)

Sample Number	Soil Ads	Aqueous Phase			Glassware*	Extractable	Non- extractable	Recovery
		Ads	Des 1	Des 2
2	27.9	41.5	14.4	8.5	1.38			93.7
3	23.9	44.9	15.1	7.8	1.16			93.0
4	18.7	57.1	15.2	7.0	1.35			99.3
5	14.1	58.3	16.6	6.4	0.92			96.4
6	12.4	62.4	16.3	6.3	0.83			98.2
Average	19.4	52.8	15.5	7.2	1.13			96.1
6'		56.2			0.18	31.2	6.8	94.4

* Radioactivity adsorbed to glass-wall of incubation tubes finally removed by extraction with methanol.

Table: Balance of Radioactivity with Soil Les Evouettes after Adsorption and Desorption (Values given in% of the Radioactivity applied)

Sample Number	Soil Ads	Aqueous Phase			Glassware*	Extractable	Non- extractable	Recovery
		Ads	Des 1	Des 2
2	33.1	38.1	19.1	9.5	0.76			100.6
3	29.7	39.6	19.6	11.2	0.68			100.7
4	25.9	45.4	19.9	10.3	0.68			102.1
5	19.7	49.5	20.3	9.4	0.52			99.5
6	18.0	51.8	20.9	9.5	0.5			100.8
Average	25.3	44.9	20.0	10.0	0.64			100.7
6'		42.5			0.06	45.6	6.3	94.4

* Radioactivity adsorbed to glass-wall of incubation tubes finally removed by extraction with methanol.

Table: Balance of Radioactivity with Soil Vetroz after Adsorption and Desorption (Values given in% of the Radioactivity applied)

Sample Number	Soil Ads	Aqueous Phase			Glassware*	Extractable	Non- extractable	Recovery
		Ads	Des 1	Des 2
2	56.7	18.8	9.4	7.2	0.73			92.8
3	54.9	21.3	11.1	8.2	0.59			96.1
4	50.5	23.2	12.0	9.3	0.61			95.6
5	46.1	26.0	14.2	9.5	0.62			96.4
6	43.8	29.1	15.2	10.4	0.45			99.0
Average	50.4	23.7	12.4	8.9	0.60			96.0
6'		23.4			0.09	60.7	11.5	95.7

* Radioactivity adsorbed to glass-wall of incubation tubes finally removed by extraction with methanol.

 

Table: Balance of Radioactivity with Soil Illarsaz after Adsorption and Desorption (Values given in% of the Radioactivity applied)

Sample Number	Soil Ads	Aqueous Phase			Glassware*	Extractable	Non- extractable	Recovery
		Ads	Des 1	Des 2
2	79.8	8.7	3.6	2.6	0.79			95.5
3	79.9	88.4	3.9	3.8	1.24			97.3
4	77.8	8.7	4.9	3.7	0.90			96.1
5	77.7	9.3	5.2	4.1	0.82			977.1
6	76.9	9.9	5.4	4.4	0.78			97.3
Average	78.4	9.0	4.6	3.7	0.91			96.7
6'		6.6			0.43	63.3	25.3	95.7

* Radioactivity adsorbed to glass-wall of incubation tubes finally removed by extraction with methanol.

Table: Freundlich Constants, Slopes and Correlation Coefficients for the Adsorption of the test substance with various Soils

Soil Type	Organic Matter [%]	Slope [1/n]	Adsorption Constant		Q-value	Correlation (r2)
			K	Koc
Lakeland	0.74	0.7899	5.54	1291	749	0.99749
Collombey	1.33	0.9523	3.10	402	233	0.99590
Les Evouettes	2.40	0.8435	7.21	518	300	0.99965
Vetroz	7.57	0.8354	13.48	307	178	0.99970
Illarsaz	33.43	0.9388	47.74	246	143	0.99904
Average				503	292

 

Table: Freundlich Constants, Slopes and Correlation Coefficients for the Desorption of the test substance with various Soils

Soil Type	Organic matter [%]	Desorption 1			Desorption 2
		1/n	Kdes 1	r2	1/n	Kdes	r2
Lakeland	0.74	0.8209	10.7	0.99856	0.8796	23.3	0.99879
Collombey	1.33	0.9413	6.2	0.99750	1.0557	17.7	0.99707
Les Evouettes	2.40	0.8376	9.7	0.99992	0.8624	15.2	0.99695
Vetroz	7.57	0.8137	16.9	0.99936	0.8075	19.8	0.99972
Illarsaz	33.43	0.8977	64.0	0.99963	0.8478	70.0	0.99597

 

Table: concentration of the test substance in aqueous Phases and in Sediment of Soil Collombey after Adsorption and Desorption Steps

Sample Number	Ci* (µg/mL)	Adsorption		Desorption 1		Desorption 2
		Ce (μg/mL)	X/m (μg/g)	Ce 1 (μg/mL)	X/m 1 (μg/g)	Ce 2 (μg/mL)	X/m 2 (μg/g)
1	0.00
2	0.20	0.123	0.372	0.034	0.244	0.014	0.183
3	0.40	0.226	0.850	0.075	0.543	0.027	0.431
4	1.00	0.592	1.991	0.175	1.310	0.066	1.034
5	1.99	1.224	3.783	0.376	2.306	0.121	1.821
6	3.99	2.500	7.324	0.711	4.466	0.222	3.593
6’	4.01	2.509	7.390
6’’	4.01	2.502	7.419

* Initial concentration of the test substance in the aqueous phases corrected for amount of test substance adsorbed to glass-walls of test tubes.

 

Table: concentration of the test substance in aqueous Phases and in Sediment of Soil Lakeland after Adsorption and Desorption Steps

Sample Number	Ci* (µg/mL)	Adsorption		Desorption 1		Desorption 2
		Ce (μg/mL)	X/m (μg/g)	Ce 1 (μg/mL)	X/m 1 (μg/g)	Ce 2 (μg/mL)	X/m 2 (μg/g)
1	0.00
2	0.20	0.066	0.653	0.027	0.539	0.012	0.483
3	0.40	0.143	1.253	0.053	1.015	0.024	0.904
4	0.99	0.454	2.643	0.139	2.045	0.058	1.782
5	1.99	0.927	5.237	0.303	3.929	0.113	3.435
6	3.98	1.983	9.865	0.604	7.302	0.221	6.329
6’	4.01	1.991	9.955
6’’	4.01	2.025	9.785

* Initial concentration of the test substance in the aqueous phases corrected for amount of test substance adsorbed to glass-walls of test tubes.    

 

Table: concentration of the test substance in aqueous Phases and in Sediment of Soil Les Evouettes after Adsorption and Desorption Steps

Sample Number	Ci* (µg/mL)	Adsorption		Desorption 1		Desorption 2
		Ce (μg/mL)	X/m (μg/g)	Ce 1 (μg/mL)	X/m 1 (μg/g)	Ce 2 (μg/mL)	X/m 2 (μg/g)
1	0.00
2	0.20	0.061	0.672	0.032	0.536	0.016	0.467
3	0.40	0.128	1.319	0.068	1.026	0.039	0.855
4	1.00	0.366	3.069	0.181	2.302	0.094	1.901
5	1.99	0.800	5.825	0.378	4.240	0.177	3.509
6	3.99	1.674	11.284	0.786	8.001	0.363	6.510
6’	4.01	1.678	11.349
6’’	4.01	1.692	11.276

* Initial concentration of the test substance in the aqueous phases corrected for amount of test substance adsorbed to glass-walls of test tubes.    

 

Table: concentration of the test substance in aqueous Phases and in Sediment of Soil Vetroz after Adsorption and Desorption Steps

Sample Number	Ci* (µg/mL)	Adsorption		Desorption 1		Desorption 2
		Ce (μg/mL)	X/m (μg/g)	Ce 1 (μg/mL)	X/m 1 (μg/g)	Ce 2 (μg/mL)	X/m 2 (μg/g)
1	0.00
2	0.20	0.034	0.794	0.020	0.709	0.014	0.646
3	0.40	0.077	1.546	0.046	1.350	0.032	1.206
4	1.00	0.210	3.776	0.125	3.250	0.090	2.849
5	1.99	0.470	7.308	0.290	6.073	0.190	5.249
6	3.99	1.051	14.138	0.628	11.491	0.415	9.681
6’	4.01	1.071	14.085
6’’	4.01	1.064	14.139

* Initial concentration of the test substance in the aqueous phases corrected for amount of test substance adsorbed to glass-walls of test tubes.    

 

Table: concentration of the test substance in aqueous Phases and in Sediment of Soil Illarsaz after Adsorption and Desorption Steps

Sample Number	Ci* (µg/mL)	Adsorption		Desorption 1		Desorption 2
		Ce (μg/mL)	X/m (μg/g)	Ce 1 (μg/mL)	X/m 1 (μg/g)	Ce 2 (μg/mL)	X/m 2 (μg/g)
1	0.00
2	0.20	0.014	0.816	0.008	0.791	0.004	0.775
3	0.40	0.027	1.627	0.016	1.571	0.012	1.520
4	0.99	0.069	4.077	0.046	3.904	0.032	3.777
5	1.99	0.147	8.122	0.096	7.760	0.072	7.472
6	3.98	0.314	16.175	0.201	15.421	0.151	14.804
6’	4.01	0.314	16.214
6’’	4.01	0.332	16.147

* Initial concentration of the test substance in the aqueous phases corrected for amount of test substance adsorbed to glass-walls of test tubes.    

Validity criteria fulfilled:

not specified

Conclusions:

The adsorption/desorption behaviour of the radiolabelled test substance has been studied in five different soil types. Based on the results obtained the test substance has to be classified as a strongly adsorbing compound.

Executive summary:

The adsorption and desorption of the test substance was studied with various soil types in accordance with OECD TG 106 and in compliance with GLP-criteria. The Freundlich adsorption constants k varied between 3.1 μg/g of soil in soil Collombey and 47.7 μg/g of soil in soil Illarsaz (humic soil) with a mean value of Q = 292 μg/g organic matter (OM) and a mean adsorption constant corrected for the organic carbon content (OC) of koc = 503 μg/g OC. The slopes 1/n for the adsorption isotherms ranged between 0.79 to 0.95, indicating that the Freundlich adsorption isotherms would not strongly follow the distribution law. Desorption data of the test substance showed that adsorption was partially irreversible. Desorption constants determined ranged from 6.2 to 64.0 μg/g of soil (first desorption) and from 15.2 to 70.0 μg/g of soil (second desorption). Recovery of all experiments ranged from 96 to 102% of the dose applied. Analysis of soil extracts of the highest test concentration showed besides the test substance no degradation products. Analysis of the supernatant aqueous phase of the same samples showed besides the parent compound (77.4 to 87.9%), two impurities and a metabolite fraction (not further identified), indicating a slight degradation of the test substance during the adsorption equilibrium.

Reference 2

Endpoint:

adsorption / desorption, other

Remarks:

Batch-Equilibrium method

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

11 Oct 1995 to 30 Jan 1996

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Pesticide EPA Assessment Guidelines, Subdivision N, Section 163-1.

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Remarks:

[14C]-labelled at position 6 of the triazine ring

Test temperature:

25 ± 1 °C

Analytical monitoring:

yes

Details on sampling:

Duplicate samples of each soil type were removed from the water bath at 2, 4, 8, and 24 hours (See 'Details on test conditions').

Matrix no.:

#1

Matrix type:

sand

% Clay:

4

% Silt:

5

% Sand:

91

% Org. carbon:

0.47

pH:

5.6

CEC:

3.5 meq/100 g soil d.w.

Bulk density (g/cm³):

1.48

Matrix no.:

#2

Matrix type:

sandy loam

% Clay:

8

% Silt:

27

% Sand:

65

% Org. carbon:

0.24

pH:

5.7

CEC:

5.3 meq/100 g soil d.w.

Bulk density (g/cm³):

1.28

Matrix no.:

#3

Matrix type:

loam

% Clay:

8

% Silt:

48

% Sand:

44

% Org. carbon:

0.24

pH:

7

CEC:

9.3 meq/100 g soil d.w.

Bulk density (g/cm³):

1.13

Matrix no.:

#4

Matrix type:

silty clay loam

% Clay:

30

% Silt:

58

% Sand:

12

% Org. carbon:

0.88

pH:

7.9

CEC:

44.3 meq/100 g soil d.w.

Bulk density (g/cm³):

1.14

Matrix no.:

#5

Matrix type:

loam

% Clay:

22

% Silt:

48

% Sand:

30

% Org. carbon:

2.06

pH:

7.1

CEC:

18.1 meq/100 g soil d.w.

Bulk density (g/cm³):

1.01

Details on matrix:

COLLECTION AND STORAGE
- Soil preparation: Before use, the soils were air dried and passed through a 2-mm sieve. The soils were completely characterized, under GLP guidelines, using the USDA classification system.

ADDITIONAL SOIL PROPERTIES PER SOIL
Soil #1
- Name: Plainfield
- Location: Hancock, Wisconsin, USA
- Horizon: A
- Taxonomic classification: Mixed, mesic, typic udipsamments
- Field moisture capacity (%, at 0.33 bar): 3.1
- Calcium: 14.4%
- Magnesium: 12.0%
- Sodium: 2.6%
- Potassium: 8.9%
- Hydrogen: 62.1%
- Clay fraction mineralogy: Chlorite, kaolinite

Soil #2
- Name: Hanford
- Location: Sanger, California, USA
- Horizon: A
- Taxonomic classification: Coarse-loamy, mixed, thermic typic xerorthenths
- Field moisture capacity (%, at 0.33 bar): 13.9
- Calcium: 47%
- Magnesium: 11%
- Sodium: 1.9%
- Potassium: 8.6%
- Hydrogen: 31.6%
- Clay fraction mineralogy: Illite dominant, kaolinite

Soil #3
- Name: Bosket
- Location: Greenville, Mississippi
- Horizon: A
- Taxonomic classification: Fine-loamy, mixed, thermic mollic hapludalfs
- Field moisture capacity (%, at 0.33 bar): 11.9
- Calcium: 64.5%
- Magnesium: 18.8%
- Sodium: 2.1%
- Potassium: 5.2%
- Hydrogen: 9.5%
- Clay fraction mineralogy: Smectite dominant,kaolinite, chlorite and illite

Soil #4
- Name: Gadsden
- Location: Yuma County, Arizona, USA
- Horizon: A
- Taxonomic classification: Fine montmoillonitic (calcareous), hyperthermic vetric torrifluvents
- Field moisture capacity (%, at 0.33 bar): 33.1
- Calcium: 70.0%
- Magnesium: 16.0%
- Sodium: 7.0%
- Potassium: 3.0%
- Hydrogen: 4.0%
- Clay fraction mineralogy: Smectite, kaolinite, chlorite, and illite

Soil #5
- Name: Ashkum-Elliott
- Location: Dewey, Illnois, USA
- Horizon: A
- Taxonomic classification: Fine, mixed, illitic mesic typic haplaquolls, mesic aquic argiudolls
- Field moisture capacity (%, at 0.33 bar): 25.7
- Calcium: 63.5%
- Magnesium: 17.5%
- Sodium: 0.6%
- Potassium: 2.0%
- Hydrogen: 16.3%
- Clay fraction mineralogy: Chlorite, illite, kaolinite and smectite

Details on test conditions:

MICROBIAL BIOMASS DETERMINATION
The soils were analyzed for the presence of microorganisms, with the exception of the Ashkum-Elliott soil. Six serial dilutions [10 g of soil in 90 mL of phosphate buffer were plated. The aerobic plate count and anaerobic plate count assays were plated using plate count agar (Difeo Laboratories) and incubated at 35°C ±2° for 48 hours ± 3 hours. Prior to incubation, the anaerobic samples were placed in an anaerobic jar containing Difeo Anaerobic System. This system contains sodium borohydride, tartaric acid, and sodium bicarbonate, and generates hydrogen and carbon dioxide while absorbing oxygen. Plates were counted by visual observation using a manual plate reader.

TEST SYSTEM
- Treatment rate: The treatment rate of the radiolabelled test substance to the top soil was approximately 1.5 ppm (1.5 μg/g), which is the approximate proposed maximum seasonal applied loading rate of the test substance.
- Desilanization of glassware: All glassware was silanized before use. The glass was rinsed with dichloromethane. After air drying, the glassware was filled with a 5% solution of dimethyldichlorosilane in toluene. The glassware was allowed to react with the silanizing reagent for a minimum of 15 minutes. The reagent was poured off, and the glassware was rinsed with copious amounts of methanol (MeOH) and dichloromethane. The glassware was oven dried at 110°C for at least 1 hour.

LIQUID SCINTILLATION COUNTING
Two liquid scintillation counters, Model Nos. LS 3801 and LS 5000TD (Beckman Instruments, Inc.) were used to measure the sample radioactivity. The instruments were calibrated daily using an unquenched Beckman calibration standard. A quench curve was established for each instrument using a set of quenched radiocarbon standards. Aliquots of supernatants and extracts were mixed with LSC cocktail (Ultima-Gold XR, Packard Instrument Company) in borosilicate glass vials (7-mL or 20-mL capacity), counted for 2 minutes, and corrected for background (cocktail) radioactivity.

EFFICIENCY OF THE SOIL OXIDATION PROCEDURE
The machine efficiency of the oxidizer (Model OX-500, R.J. Harvey Instrument Corporation) was determined before every series of soil combustions by oxidizing a known amount of Spec-Chee radiocarbon standard (Packard Instrument Company) on a combustion cone. The resulting radioactive carbon dioxide (14CO2) was trapped with 15-mL aliquots of Carbo-Sorb E:Perma-Fluor E+ (3:4) (Packard Instrument Company) contained in glass vials (20-mL capacity), and the trapped radioactivity was directly measured by LSC. The machine combustion efficiency was greater than 95% for all analyses. The efficiency of the soil oxidation procedure was determined before every series of soil combustions using duplicate aliquots of each untreated soil dosed with known amounts of the radiolabelled test substance. The dosed soil aliquots were oxidized by combustion, and the resulting 14CO2 was quantitated by LSC. The amount of radioactivity recovered from each sample was divided by the amount of radioactivity applied to the sample to determine an oxidation efficiency factor (sample efficiency). Sample efficiencies ranged from 95.2% to 101.6%. Because the sample efficiencies were greater than 95%, radioactivity values for the soil oxidations were not corrected for oxidation efficiency.

Sample No.:

#1

Duration:

24 h

Initial conc. measured:

>= 0.54 - <= 4.77 mg/kg soil d.w.

pH:

5.6

Temp.:

25 °C

Remarks:

Four concentrations were used: 0.540, 1.07, 2.53, and 4.77 μg/mL

Sample No.:

#2

Duration:

24 h

Initial conc. measured:

>= 0.54 - <= 4.77 mg/kg soil d.w.

pH:

5.7

Temp.:

25 °C

Remarks:

Four concentrations were used: 0.540, 1.07, 2.53, and 4.77 μg/mL

Sample No.:

#3

Duration:

24 h

Initial conc. measured:

>= 0.54 - <= 4.77 mg/kg soil d.w.

pH:

7

Temp.:

25 °C

Remarks:

Four concentrations were used: 0.540, 1.07, 2.53, and 4.77 μg/mL

Sample No.:

#4

Duration:

24 h

Initial conc. measured:

>= 0.54 - <= 4.77 mg/kg soil d.w.

pH:

7.9

Temp.:

25 °C

Remarks:

Four concentrations were used: 0.540, 1.07, 2.53, and 4.77 μg/mL

Sample No.:

#5

Duration:

24 h

Initial conc. measured:

>= 0.51 - <= 5.36 mg/kg soil d.w.

pH:

7.1

Temp.:

25 °C

Remarks:

Four concentrations were used: 0.510, 1.03, 2.66, and 5.36 μg/mL

Sample no.:

#1

Duration:

24 h

pH:

5.6

Temp.:

25 °C

Remarks:

Plainfield sand: Percent adsorption to soil was 10.7 - 36.1

Sample no.:

#2

Duration:

24 h

pH:

5.7

Temp.:

25 °C

Remarks:

Hanford sady loam: Percent adsorption to soil was 23.8 - 60.8

Sample no.:

#3

Duration:

24 h

pH:

7

Temp.:

25 °C

Remarks:

Bosket loam: Percent adsorption to soil was 36.3 - 66.5

Sample no.:

#4

Duration:

24 h

pH:

7.9

Temp.:

25 °C

Remarks:

Gadsen silty clay loam: Percent adsorption to soil was 46.5 - 75.5

Sample no.:

#5

Duration:

24 h

pH:

7.1

Temp.:

25 °C

Remarks:

Ashkum-Elliot: Percent adsorption to soil was 52.0 - 75.7

Computational methods:

Correlation coefficient, slope, intercept values, mean, and standard deviation were the only statistical methods performed.

Key result

Sample No.:

#1

Type:

other: Freundlich Koc (Kfoc)

Value:

1 394 L/kg

pH:

5.6

Temp.:

25 °C

Matrix:

Sand soil (Plainfield)

% Org. carbon:

0.47

Remarks on result:

other: An overview of all adsorption and desorption coefficients is provided in 'Any other information on results incl. tables'.

Key result

Sample No.:

#2

Type:

other: Freundlich Koc (Kfoc)

Value:

5 833 L/kg

pH:

5.7

Temp.:

25 °C

Matrix:

Sandy loam (Hanford)

% Org. carbon:

0.24

Key result

Sample No.:

#3

Type:

other: Freundlich Koc (Kfoc)

Value:

7 875 L/kg

pH:

7

Temp.:

25 °C

Matrix:

Loam (Bosket)

% Org. carbon:

0.24

Key result

Sample No.:

#4

Type:

other: Freundlich Koc (Kfoc)

Value:

3 080 L/kg

pH:

7.9

Temp.:

25 °C

Matrix:

Silty clay loam (Gadsden)

% Org. carbon:

0.88

Key result

Sample No.:

#5

Type:

other: Freundlich Koc (Kfoc)

Value:

1 500 L/kg

pH:

7.1

Temp.:

25 °C

Matrix:

Loam (Elliott-Ashkum)

% Org. carbon:

2.06

Adsorption and desorption constants:

An overview of all adsorption and desorption coefficients is provided in 'Any other information on results incl. tables'.

Recovery of test material:

Total recovery:
- Soil #1 (Plainfield): 97.5 - 105.1%
- Soil #2 (Hanford): 96.7 - 104.7%
- Soil #3 (Bosket): 97.2 - 102.8%
- Soil #4 (Gadsden): 95.2 - 102.6%
- Soil #5 (Ashkum-Elliott): 95.6 - 98.5%
An overview of all individual recovery rates per soil type is provided in 'Any other information on results incl. tables'.

Concentration of test substance at end of adsorption equilibration period:

An overview of all individual adsorption concentrations per soil type is provided in 'Any other information on results incl. tables'.

Concentration of test substance at end of desorption equilibration period:

An overview of all individual desorption concentrations per soil type is provided in 'Any other information on results incl. tables'.

Remarks on result:

other: see 'Any other information on results incl. tables'.

Remarks on result:

other: see 'Any other information on results incl. tables'.

Transformation products:

yes

Remarks:

Only minor quantities (≤ 2%) of M1 and M2 were identified.

Details on results (Batch equilibrium method):

SOLUBILITY
The radiolabelled test substance was soluble in aqueous 0.01M CaCl2 at all concentrations tested. Regression analysis demonstrated that the plot of applied concentration versus experimental concentration was linear with a y-intercept of 0.0885, a slope of 0.940, and a correlation coefficient of 1.00 for Plainfield, Hanford, Bosket, and Gadsden soils. The plot of applied concentration versus experimental concentration was also linear with a y-intercept of -0.0068, a slope of 1.062, and a correlation coefficient of 1.00 for Ashkum Elliott soil.

ADSORPTION
A general pattern of increased adsorption of the radiolabelled test substance to soil with decreasing concentration was observed for all soil types. Regression analysis of the solution and soil log concentrations at four test material levels was linear for all of the soil types, indicating that the adsorption of the radiolabelled test substance to soil followed the Freundlich equation. The correlation coefficients from the linear regression analyses were 0.941 for Plainfield sand, 0.983 for Hanford sandy loam, 0.999 for Bosket loam, 0.994 for Gadsden silty clay loam, and 0.999 for Ashkum-Elliott loam. The calculated Kd-a and Koc-a values are presented in ‘Any other information on results incl. tables’.

Using linear regression, the apparent relationship between adsorption and the soil characteristics was confirmed by correlating the Kd-a values with the organic matter content, clay content, cation exchange capacity, and pH:
- Correlation coefficient organic matter content: 0.756
- Correlation coefficient clay content: 0.870
- Correlation Cation exchange capacity (meq/100 g): 0.705
- Correlation coefficient pH: 0.858

The cation exchange capacity, which represents the net contribution of the organic matter and clay content to the total number of potential binding sites in the soil, does not provide a good correlation to the Kd-a values. While the clay content and pH provides a correlation to the Kd-a values, no correlation was observed between the Kd-a values and the organic matter content.

A mobility class based on the Koc-a values was assigned to each soil tested:
- Soil #1 (Plainfield sand): Low
- Soil #2 (Hanford sandy loam): Immobile
- Soil #3 (Bosket loam): Immobile
- Soil #4 (Gadsden silty clay loam): Slight
- Soil #5 (Ashkum-Elliott loam): Low
The mobility classification of the radiolabelled test substance is low for Plainfield sand and Ashkum-Elliott loam, immobile for Hanford sandy loam and Bosket loam, and slight for Gadsden silty clay loam, based on the Koc-a values. These data indicate that the potential of radiolabelled test substance to leach through soil to groundwater is low.

DESORPTION
A general pattern of increased desorption of the radiolabelled test substance from soil with increasing concentrations was observed for all soil types. Regression analysis of the solution and soil log concentrations at four test material levels was linear for all four soil types, indicating that the desorption of the radiolabelled test substance from soil followed the Freundlich equation. The correlation coefficients for the linear regression analyses were 0.989 for Plainfield sand, 0.996 for Hanford sandy loam, 0.998 for Bosket loam, 0.999 for Gadsden
silty clay loam, and 0.998 for Ashkum-Elliott loam. The calculated Kd-d and Koc-d values are presented in ‘Any other information on results incl. tables’.


MATERIAL BALANCE
The material balance for the five soils ranged from 95.2% to 105.1 %, indicating that any radioactivity lost because of uncaptured volatiles or adsorption to the sample container was minimal.

Table: Calculated Kd-a And Koc-a Values

Soil	Kd-a	Koc-a
Plainfield sand	6.55	1394
Hanford sandy loam	14.0	5833
Bosket loam	18.9	7875
Gadsden silty clay loam	27.1	3080
Ashkum-Elliott loam	30.9	1500

 

Table: Calculated Kd-d And Koc-d Values

Soil	Kd-d	Koc-d
Plainfield sand	8.41	1789
Hanford sandy loam	18.9	7875
Bosket loam	37.7	15708
Gadsden silty clay loam	38.9	4420
Ashkum-Elliott loam	47.5	2306

Table: Adsorption of the radiolabelled test substance in Aqueous 0.01M Ca02 to Plainfield Sand, Hanford Sandy Loam and Bosket Loam Soils after Various Equilibration Times

Equilibration Time (Hours)	Adsorption to soil relative to initial Solution Concentration*
	Individual (%)	Mean (%)
Plainfield Sand
2	21.0	20.7
2	20.3
4	20.9	20.6
4	20.2
8	21.1	21.9
8	22.7
24	24.2	23.9
24	23.5
Hanford Sandy Loam
2	36.1	35.4
2	34.6
4	34.5	34.3
4	34.0
8	35.3	35.5
8	35.7
24	37.5	38.5
24	39.4
Bosket Loam
2	32.1	33.5
2	34.8
4	33.2	32.0
4	30.7
8	32.2	31.9
8	31.5
24	34.5	33.9
24	33.2
Gadsden Silty Clay Loam
2	40.3	39.9
2	39.4
4	38.6	39.0
4	39.4
8	39.1	39.2
8	39.3
24	40.2	40.9
24	41.6
Ashkum-Elliott Loam
2	48.5	48.6
2	48.6
4	48.1	48.3
4	48.5
8	52.9	52.1
8	51.3
24	52.0	51.5
24	51.0

* Initial test material concentration in solution was 5.02 μg/mL of 0.01 M CaCl2 solution and 5.36 μg/mL of 0.01 M CaCl2 solution for the Ashkum-Elliott loam soil.

 

Table: Linear Regression Analysis of the Adsorption and Desorption Soil and Solution Natural Log Concentration of the radiolabelled test substance

Soil	Slope (ln)	Correlation coefficient	Equilibrium Constant (Kd)	Sorption Coefficient (Koc)
Adsorption*
Plainfield sand	0.412	0.941	6.55	1394
Hanford sandy loam	0.445	0.983	14.0	5833
Bosket loam	0.556	0.999	18.9	7875
Gadsden silty clay loam	0.569	0.994	27.1	3080
Ashkum-Elliott loam	0.652	0.999	30.9	1500
Desorption**
Plainfield sand	0.667	0.989	8.41	1789
Hanford sandy loam	0.703	0.996	18.9	7875
Bosket loam	0.661	0.998	37.7	15708
Gadsden silty clay loam	0.643	0.999	38.9	4420
Ashkum-Elliott loam	0.706	0.998	47.5	2306

 

Table: Adsorption of the radiolabelled test substance after Equilibrium* 

Initial Solution concentration (µg/mL)**	Concentration				Adsorption to Soil
	Solution (µg/g)	Solution (ln µg/g)	Soil (µg/g)	Soil (ln µg/g)	Inidividual (%)	Mean (%)
Plainfield Sand
4.77	4.27	1.4516	9.99	2.3016	10.5	10.7
4.77	4.25	1.4469	10.4	2.3418	10.9
2.53	1.99	0.6881	10.9	2.3888	21.6	21.3
2.53	2.00	0.6931	10.6	2.3609	21.0
1.07	0.763	-0.2705	6.01	1.7934	28.4	28.9
1.07	0.754	-0.2824	6.21	1.8262	29.3
0.540	0.348	-1.0556	3.84	1.3455	35.6	36.1
0.540	0.343	-1.0700	3.91	1.3635	36.5
Hanford Sandy Loam
4.77	3.63	1.2892	22.6	3.1179	23.9	23.8
4.77	3.65	1.2947	22.5	3.1135	23.6
2.53	1.56	0.4447	19.4	2.9653	38.4	38.2
2.53	1.57	0.4511	19.1	2.9497	37.9
1.07	0.516	-0.6616	10.9	2.3888	51.5	51.8
1.07	0.511	-0.6714	11.0	2.3979	52.0
0.540	0.208	-1.5702	6.64	1.8931	61.6	60.8
0.540	0.216	-1.5325	6.47	1.8672	60.0
Bosket Loam
4.77	3.04	1.1119	34.3	3.5351	36.2	36.3
4.77	3.04	1.1119	34.6	3.5439	36.3
2.53	1.40	0.3365	22.6	3.1179	44.8	45.2
2.53	1.38	0.3221	23.1	3.1398	45.6
1.07	0.454	-0.7897	12.1	2.4932	57.4	58.3
1.07	0.434	-0.8347	12.5	2.5257	59.2
0.540	0.181	-1.7093	7.15	1.9671	66.5	66.5
0.540	0.181	-1.7093	7.14	1.9657	66.5
Gadsden Silty Clay Loam
4.77	2.48	0.9083	45.7	3.8221	48.0	46.5
4.77	2.62	0.9632	42.7	3.7542	45.0
2.53	1.09	0.0862	28.6	3.3534	56.8	58.0
2.53	1.03	0.0296	29.9	3.3979	59.2
1.07	0.308	-1.1777	15.0	2.7081	71.1	70.4
1.07	0.324	-1.1270	14.8	2.6946	69.6
0.540	0.143	-1.9449	7.92	2.0694	73.6	75.5
0.540	0.123	-2.0956	8.31	2.1175	77.3
Ashkum-Elliott Loam
5.36	2.54	0.9322	56.2	4.0289	52.5	52.0
5.36	2.60	0.9555	55.1	4.0091	51.4
2.66	1.03	0.0296	32.7	3.4874	61.3	60.7
2.66	1.06	0.0583	32.0	3.4657	60.1
1.03	0.311	-1.1680	14.4	2.6672	69.8	71.0
1.03	0.288	-1.2448	14.8	2.6946	72.1
0.510	0.124	-2.0875	7.68	2.0386	75.7	75.7
0.510	0.124	-2.0875	7.59	2.0268	75.6

* The soil:solution ratio was 1:20. Samples were equilibrated 24 hours before analysis.

** The beginning concentration of the radiolabelled test substance in the 0.01M CaCl2 sample solution

Table: Desorption of the radiolabelled test substance Equilibrium*

 

Initial Solution concentration (µg/mL)**	Concentration				Desorption to Soil
	Solution (µg/g)	Solution (ln µg/g)	Solution (µg/g)	Solution (ln µg/g)	Individual (%)	Mean (%)
Plainfield Sand
4.77	0.449	-0.8007	5.01	1.6114	64.5	64.4
4.77	0.481	-0.7319	5.43	1.6919	64.2
2.53	0.298	-1.2107	3.90	1.3610	60.8	61.7
2.53	0.297	-1.2140	3.60	1.2809	62.5
1.07	0.170	-1.7720	2.33	0.8459	59.5	59.3
1.07	0.175	-1.7430	2.44	0.8920	59.1
0.540	0.0908	-2.3991	1.73	0.5481	51.6	50.7
0.540	0.0923	-2.3827	1.88	0.6313	49.7
Hanford Sandy Loam
4.77	0.652	-0.4277	13.7	2.6174	48.9	49.0
4.77	0.650	-0.4308	13.7	2.6174	49.0
2.53	0.418	-0.8723	9.69	2.2711	46.8	44.9
2.53	0.381	-0.9650	10.2	2.3224	43.0
1.07	0.201	-1.6045	6.45	1.8641	38.7	39.4
1.07	0.212	-1.5512	6.42	1.8594	40.1
0.540	0.113	-2.1804	3.95	1.3737	37.2	36.9
0.540	0.111	-2.1982	3.91	1.3635	36.6
Bokset Loam
4.77	0.576	-0.5516	25.2	3.2268	31.7	31.1
4.77	0.545	-0.6070	25.7	3.2465	30.4
2.53	0.280	-1.2730	15.8	2.7600	26.5	25.8
2.53	0.271	-1.3056	16.6	2.8094	25.1
1.07	0.112	-2.1893	9.55	2.2565	19.2	20.6
1.07	0.132	-2.0250	9.56	2.2576	21.9
0.540	0.0584	-2.8404	5.71	1.7422	17.2	17.4
0.540	0.0592	-2.8268	5.64	1.7299	17.6
Gadsdem Silty Clay Loam
4.77	0.716	-0.3341	30.6	3.4210	32.4	32.2
4.77	0.704	-0.3510	30.8	3.4275	31.9
2.53	0.351	-1.0470	19.8	2.9857	26.6	26.2
2.53	0.352	-1.0441	20.4	3.0155	26.2
1.07	0.138	-1.9805	11.2	2.4159	20.1	20.3
1.07	0.143	-1.9449	11.4	2.4336	20.5
0.540	0.0631	-2.7630	6.33	1.8453	17.0	17.0
0.540	0.0645	-2.7411	6.68	1.8991	16.5
Ashkum-Elliott Loam
5.36	0.773	-0.2575	38.4	3.6481	29.3	29.1
5.36	0.751	-0.2863	38.1	3.6402	28.9
2.66	0.363	-1.0134	23.8	3.1697	24.0	23.8
2.66	0.354	-1.0385	23.4	3.1527	23.8
1.03	0.125	-2.0794	11.2	2.4159	18.7	18.4
1.03	0.123	-2.0956	11.5	2.4423	18.0
0.510	0.0540	-2.9188	6.13	1.8132	15.3	15.3
0.510	0.0589	-2.8319	5.96	1.7851	16.7

* The soil:solution ratio was 1:20. Samples were equilibrated 24 hours before analysis.

** The beginning concentration of the radiolabelled test substance in the 0.01M CaCl2 sample solution.

 

Table: Accountability of Radioactivity

Initial Solution concentration (µg/mL)	Applied		Adsorption		Desorption		Combusted Soil		Total	Recovery
	Dpm (a)	µg/mL (b)	Dpm (c)	µg/mL (b)	Dpm (d)	µg/mL	Dpm (e)	µg/g	Dpm	(%)
Plainfield Sand
4.77	4351150	4.77	3894150	4.27	417251	0.449	229352	5.01	4540753	104.4
4.77	4351150	4.77	3875570	4.25	446610	0.481	248962	5.43	4571142	105.1
2.53	2310680	2.53	1812350	1.99	276676	0.298	178209	3.90	2267235	98.1
2.53	2310680	2.53	1825190	2.00	275102	0.297	164932	3.60	2265224	98.0
1.07	972220	1.07	696490	0.763	156921	0.170	106670	2.33	960081	98.8
1.07	972220	1.07	687730	0.754	161716	0.175	111837	2.44	961283	98.9
0.540	492870	0.540	317370	0.348	84037	0.0908	78912	1.73	480319	97.5
0.540	492870	0.540	312790	0.343	85492	0.0923	86678	1.88	484960	98.4
Hanford Sandy Loam
4.77	4351150	4.77	3312190	3.63	605305	0.652	632904	13.7	4550399	104.
4.77	4351150	4.77	3325850	3.65	603108	0.650	627002	13.7	4555960	104.
2.53	2310680	2.53	1423450	1.56	389707	0.418	443454	9.69	2256611	97.
2.53	2310680	2.53	1433840	1.57	354471	0.381	469955	10.2	2258266	97.
1.07	972220	1.07	471260	0.516	186911	0.201	295815	6.45	953986	98.
1.07	972220	1.07	466530	0.511	197039	0.212	294777	6.42	958346	98.
0.540	492870	0.540	189370	0.208	106789	0.113	180474	3.95	476633	96.
0.540	492870	0.540	196990	0.216	103222	0.111	178759	3.91	478971	97.
Bosket Loam
4.77	4351150	4.77	2776780	3.04	537996	0.576	1157059	25.2	4471835	102.8
4.77	4351150	4.77	2773050	3.04	510926	0.545	1172374	25.7	4456350	102.4
2.53	2310680	2.53	1275940	1.40	260630	0.280	723241	15.8	2259811	97.8
2.53	2310680	2.53	1258040	1.38	252838	0.271	755896	16.6	2266774	98.1
1.07	972220	1.07	413970	0.454	104445	0.112	439523	9.55	957938	98.5
1.07	972220	1.07	396360	0.434	123164	0.132	439255	9.56	958779	98.6
0.540	492870	0.540	164880	0.181	54415	0.0584	261908	5.71	481203	97.6
0.540	492870	0.540	165090	0.181	55255	0.0592	258948	5.64	479293	97.2
Gadsden Silty Clay Loam
4.77	4351150	4.77	2261120	2.48	672709	0.716	1400540	30.6	4334369	99.6
4.77	4351150	4.77	2392620	2.62	660599	0.704	1412894	30.8	4466113	102.6
2.53	2310680	2.53	997870	1.09	329631	0.351	908612	19.8	2236113	96.8
2.53	2310680	2.53	941790	1.03	330497	0.352	931705	20.4	2203992	95.4
1.07	972220	1.07	280850	0.308	129644	0.138	515486	11.2	925980	95.2
1.07	972220	1.07	295520	0.324	134060	0.143	519448	11.4	949028	97.6
0.540	492870	0.540	130360	0.143	59230	0.0631	289970	6.33	479560	97.3
0.540	492870	0.540	111880	0.123	60533	0.0645	306213	6.68	478626	97.1
Ashkum-Elliott Loam
5.36	4888990	5.36	2321250	2.54	726800	0.773	1753662	38.4	4801712	98.2
5.36	4888990	5.36	2375600	2.60	704996	0.751	1736431	38.1	4817027	98.5
2.66	2430170	2.66	941480	1.03	341217	0.363	1081419	23.8	2364116	97.3
2.66	2430170	2.66	969940	1.06	332068	0.354	1065757	23.4	2367765	97.4
1.03	940720	1.03	284050	0.311	117327	0.125	510646	11.2	912023	96.9
1.03	940720	1.03	262790	0.288	115339	0.123	526069	11.5	904198	96.1
0.510	464950	0.510	112810	0.124	50829	0.0540	281087	6.13	444726	95.7
0.510	464950	0.510	113400	0.124	55369	0.0589	275893	5.96	444662	95.6

a) Based on radioassay of treatment solutions (0.01M CaCl2).

b) Specific activity was 91242 dpm/μg.

c) The dpm remaining in adsorption solution after equilibrium.

d) The dpm in desorption solution minus dpm in adsorption solution remaining in soil after equilibrium.

e) The dpm remaining on soil minus dpm in desorption solution remaining in soil after desorption.

Validity criteria fulfilled:

not specified

Conclusions:

The radiolabelled test substance was soluble in aqueous 0.01M CaCl2 at all concentrations tested: 0.540, 1.07, 2.53, and 4.77 μg/mL for Plainfield, Hanford, Bosket, and Gadsden soils; and 0.510, 1.03, 2.66, and 5.36 μg/mL for Ashkum-Elliott soil. Minimal degradation of the test material in the test system was observed over 24 hours. Relatively high adsorption of the test substance to soil was observed for all soils tested. Based on estimations of relative mobility using Koc-a values, the potential for the radiolabelled test substance to leach through soil to groundwater is low for all soil types tested.

- RAR interpretation statement: The RMS considered that three of the five used soils (Plainfield, Hanford and Bosket) were not suitable according to OECD 106 to derive reliable adsorption endpoints and should not be included in further risk assessment.

Executive summary:

The adsorption and desorption characteristics of the test substance on five representative agricultural soils were studied in accordance with the Environmental Protection Agency Pesticide Assessment Guidelines, Subdivision N, Section 163-1 and in compliance with GLP. Samples were prepared for Plainfield sand (Soil #1), Hanford sandy (Soil #2) loam, Bosket loam (Soil #3), Gadsden silty clay loam (Soil #4), and Ashkum-Elliott loam (Soil $5) at a soil:solution ratio of 1:20 (g/mL). Four concentrations of the radiolabelled test substance in aqueous 0.01M calcium chloride (CaCl2) were used: 0.540, 1.07, 2.53, and 4.77 μg/ml for Plainfield, Hanford, Bosket, and Gadsden soils; and 0.510, 1.03, 2.66, and 5.36 μg/ml for Ashkum-Elliott soil. These samples were equilibrated in a shaking water bath for 24 hours at 25°C ±1 °, followed by vortexing and centrifugation. The resulting supernatant was analyzed by liquid scintillation counting (LSC) to determine the disappearance of radioactivity from solution as a measure of test material adsorption to soil. The supernatant was then removed from each sample and replaced with an equal volume of untreated 0.01M CaCl2. The samples were equilibrated for 24 hours at 25°C ±1 °, followed by vortexing and centrifugation. The supernatant was analyzed by LSC to determine desorption. The radioactivity remaining in the soil after desorption was determined by oxidation followed by LSC analysis.

Linear regression analysis of the adsorption data for all soil types demonstrated that adsorption of the radiolabelled test substance followed the Freundlich equation. The adsorption and desorption equilibrium constants (Kd-a and Kd-d respectively), and the adsorption and desorption coefficients (Koc-a and Koc-d, respectively) were determined in this study. The Koc-a for Soils #1-5 were 1394, 5833, 7875, 3080, 1500 L/kg, respectively. The Koc-d for Soils #1-5 were 1789, 7875, 15708, 4420, 2306 L/kg, respectively. The test material was found to be relatively stable in the test system for all soils tested over 24 hours. After 24 hours, the amount of unchanged radiolabelled test substance detected was 94.0% for Plainfield sand, 96.8% for Hanford sandy loam, 96.7% for Bosket loam, 93.0% for Gadsden silty clay loam, and 94.9% for Ashkum-Elliott samples. In aqueous 0.01M CaCl2, the radiolabelled test substance was stable over a 24-hour interval. The radiolabelled test substance was determined to be soluble at the eight concentrations tested. Based on estimations of relative mobility using Koc-a values, the potential for the radiolabelled test substance to leach through soil to groundwater is low for all soils tested.

Description of key information

The adsorption values of the active substance pymetrozine from the two studies Gonzales-Valero (1993) and Gohdes (1996) are tabulated below. An arithmetic mean Kfoc value of 1049 L/kg is used for further risk assessment.

Key value for chemical safety assessment

Koc at 20 °C:

1 049

Additional information

Table: Overview of available data on adsorption / desorption of the test item

Method			Guideline / GLP	Endpoint	Value	Reference
Test medium	pH	%OC
Loamy sand (Collombey, CH)	7.0	0.76	OECD TG 106 / GLP	Kfoc-Ads	402	Gonzalez-Valero, 1993
Sand (Lakeland, FL, USA)	5.7	0.43		Kfoc-Ads	1291
Silt loam (Les Evouettes, CH)	5.7	1.39		Kfoc-Ads	518
Silt loam (Vetroz, CH)	7.1	4.39		Kfoc-Ads	307
Humic soil (Illarsaz, CH)	6.6	19.34		Kfoc-Ads	246
Sand (Plainfield)**	5.6	0.46**	EPA Subdivision N, Section 163-1	Kfoc-Ads	1394	Gohdes, 1996
Sandy loam (Hanford)*	5.7	0.23*		Kfoc-Ads	5833
Loam (Bosket)*	7.0	0.23*		Kfoc-Ads	7875
Silty clay loam (Gadsden)	7.9	0.87		Kfoc-Ads	3080
Loam (Ashkum-Elliott	7.1	2.03		Kfoc-Ads	1500
Arithmetic mean (n = 7)					1049

* organic carbon content < 0.3 %

** very low adsorption to soil was measured, measurement uncertainties may occur due to low chosen soil/solution ratio