1-[(4-chlorophenyl)methyl]-1-cyclopentyl-3-phenylurea

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:

1989-02-27

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: US FIFRA N-163-1 40 CFR, Sec. 158.130 & 158.50

Deviations:

yes

Remarks:

The history of the soil with respect to the use of pesticides is not given.

GLP compliance:

yes (incl. QA statement)

Remarks:

Good laboratory practice requirements of 40 CFR Part 160 do not apply to the study described.

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

25°C

Analytical monitoring:

yes

Details on sampling:

- Concentrations: 0.0179, 0.0915, 0.143 and 0.186 mg/L
- Sampling interval: 0, 4, 6, 8, 16, 24, 36, 48 hours
- Sample storage before analysis: refrigerated

Details on matrix:

Four soils were used; the soil characterisation is given in Table 1.

The history of the soil with respect to the use of pesticides is not given. The appropriate soil to water ratio for the four soils was determined in a preliminary study. In the definitive test, each soil experiment was performed in duplicate at four test substance concentrations (measured concentrations 0.0179, 0.0915, 0.143 and 0.186 mg/L).

Details on test conditions:

TEST CONDITIONS
- pH: 6.96 - 7.51

TEST SYSTEM
- Type, size and further details on reaction vessel: Ten-mL Pyrex culture tubes with teflon lined screw caps were used as sample containers. The culture tubes and caps were sterilized by autoclaving at 250°F and 15 psi for one hour.

- Water filtered (i.e. yes/no; type of size of filter used, if any): Yes, 0.22 micron filter.
- Amount of soil: 1 g
- Number of reaction vessels: Two replicates each of the four soil types were sampled

The test substance was dosed (after evaporation from the solvent) from a 0.01M CaCl2 solution in sterile culture tubes, each containing one gram (dry weight) of soil. The soil suspensions were shaken in the dark, on a mechanical shaker, in an environmental controlled room (temp = 25 ± 2ºC) for six hours. Subsequently, the vessels were centrifuged and the supernatant was removed and the volume was recorded. The radioactivity of the supernatant was determined in triplicate by LSC analysis and the stability of the compound by TLC. For desorption purposes, appropriate volumes of fresh 0.01M CaCl2 solution (equal to the amount removed after centrifugation) were added to each sample and soil suspensions were shaken for 24h and subsequently treated similar as during the adsorption process. At the end of the test the remaining soil was extracted to characterize the adsorbed 14C activity in the soil.

Key result

Sample No.:

#1

Type:

Kd

Value:

55 L/kg

Temp.:

25 °C

Matrix:

sand

% Org. carbon:

0.526

Remarks on result:

other: KFoc: 10441, 1/n:1.1770

Key result

Sample No.:

#2

Type:

Kd

Value:

28.4 L/kg

Temp.:

25 °C

Matrix:

Sandy loam

% Org. carbon:

0.577

Remarks on result:

other: KFoc: 4912, 1/n: 1.0519

Key result

Sample No.:

#3

Type:

Kd

Value:

36.9 L/kg

Temp.:

25 °C

Matrix:

Silt loam

% Org. carbon:

1.53

Remarks on result:

other: KFoc: 2414, 1/n: 0.9058

Key result

Sample No.:

#4

Type:

Kd

Value:

56.7 L/kg

Temp.:

25 °C

Matrix:

Clay loam

% Org. carbon:

1.16

Remarks on result:

other: KFoc: 4899, 1/n: 1.2058

Recovery of test material:

The total radioactivity recoveries for sand, sandy loam, silt loam and clay loam were 106%, 91.7%, 103% and 106%. The equilibrium pH of the adsorption phase, as measured in each sample, varied between 6.96 and 7.51. LSC analysis of a duplicate control containing the aqueous test solution without soil, in the preliminary test, showed that there was no adsorption to the glass walls of the test tubes.

Concentration of test substance at end of adsorption equilibration period:

At the end of the adsorption phase, the percentage Pencycuron in the soil extracts was 64.2, 67.8, 51.9 and 73.5 after six hours equilibration in sand, sandy loam, silt loam and clay loam, respectively.

Concentration of test substance at end of desorption equilibration period:

After desorption the percentage Pencycuron in the soil extracts was 85.0, 92.5, 87.3 and 84.6, showing that Pencycuron is weekly desorbed.

Details on results (Batch equilibrium method):

PRELIMINARY TEST
- Other: 1 to 10 soil to water ratio with an equilibrium time of 6 hours were the appropriate difinitive study parameters for all four soil types.

MAIN TEST: PERFORMANCE
The adsorption constants Kd and Koc, as calculated from the Freundlich isotherms for the four soils, ranged from 28.4 to 56.7 L/kg and 2414 to 10441 L/kg, respectively. The desorption values were from 48.2 to104 L/kg and from 5560 to 19829 L/kg, respectively. The results of the test as adsorption and desorption coefficients and the Freundlich constants 1/n are summarized in Table 2.

Table 2: Adsorption and desorption coefficients of Pencycuron in four soils

Soil type	% organic carbon	adsorption in	L/kg		desorption
		Kd	KFoc	1/n	Kd	Koc	1/n
sand	0.526	55.0	10441	1.1770	104	19829	1.2078
sandy loam	0.577	28.4	4912	1.0519	48.2	8329	1.0709
silt loam	1.53	36.9	2414	0.9058	99.6	6526	1.0615
clay loam	1.16	56.7	4899	1.2058	64.4	5560	1.1173

1. TLC of the 2 mg/L test solution at test inititation (pencycuron represented 89.7% of the radioactivity) and after equilibration (pencycuron represented 64.2%, 67.8%, 51.9% and 73.5% of the radioactivity in sand, sandy loam, silt loam and clay loam, respectively) showed that pencycuron was not stable in the test solution. TLC of soil extracts from post-desorbed soils showed that in extracts of sand, sandy loam, silt loam and clay loam, respectively, pencycuron represented 85.0%, 92.5%, 87.3% and 84.6% of the radioactivity. The amount of test material adsorbed to soil was calculated as the difference between the amount of radioactivity present in the adsorption solution after adsorption and that initially added to each tube. Since this method involves no correction for degradation in the aqueous phase, the amount of pencycuron adsorbed to soil was underestimated by this method, and the equilibrium concentration of pencycuron overestimated, hence the adsorption coefficients are underestimated. Although there is some doubt about the accuracy of the reported Freundlich adsorption coefficients, they are accepted as worst case values.


2. Sorption in these four soils was not related to soil organic carbon content (linear regression analysis of the K_F values versus % oc gave r² = 0002), and also not to soil pH (r² = 0.26 for plot of K_F values versus soil pH) or clay content (r² = 0.03 for plot of K_F values versus percentage clay).

Validity criteria fulfilled:

yes

Remarks:

Minor deviations; Some degradation was observed in the study, so underestimates the adsorption to soil. These were accepted as being worst case values. The history of the soil with respect to the use of pesticides is not given. The study was accepted.

Conclusions:

The adsorption constants Kd and Koc, as calculated from the Freundlich isotherms for the four soils, ranged from 28.4 to 56.7 L/kg and 2414 to 10441 L/kg, respectively. The desorption values were from 48.2 to104 L/kg and from 5560 to 19829 L/kg, respectively. 1/n ranged from 1.0615 to 1.2078.

Executive summary:

The adsorption/desorption test was performed with the radio-labelled active substance [methylene-14C]Pencycuron using 4 soils, sand, sandy loam, silt loam and a clay loam.

each soil experiment was performed in duplicate at four test substance concentrations (measured concentrations 0.0179, 0.0915, 0.143 and 0.186 mg/L). The test substance was dosed (after evaporation from the solvent) from a 0.01M CaCl2 solution in sterile culture tubes, each containing one gram (dry weight) of soil. The soil suspensions were shaken in the dark, on a mechanical shaker, in an environmental controlled room (temp = 25 ± 2ºC) for six hours. Subsequently, the vessels were centrifuged and the supernatant was removed and the volume was recorded. The radioactivity of the supernatant was determined in triplicate by LSC analysis and the stability of the compound by TLC.

Following the desorption soils were extracted to charaterize adsorbed radioactivity in the soil.

Description of key information

The calculated KFoc(ads) values varied between 2414 and 10441 L/kg (median value: 4906 L/kg). The Freundlich exponents 1/n were in the range of 0.9058 to 1.1770.

 

Test Type	Result	Assessment	Reference
Batch adsorption study to US FIFRA N-163-1 guidelines	KFoc range 2414 to 10441 L/kg (median value of 4906 L/kg) reported with 1/n of 0.9058 to 1.1770. Some deficiencies in study- but accepted as providing worst case values.	Key study	Daly (1989)

Key value for chemical safety assessment

Koc at 20 °C:

4 906