diuron (ISO); 3-(3,4-dichlorophenyl)-1,1-dimethylurea

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP Guideline Study

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes (incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Test temperature:

20 °C

Details on study design: HPLC method:

The HPLC system consisted of the following hardware components:
HPLC Pump: DIONEX P680
Autosampler:: DIONEX ASI-100
UV detector: DIONEX UVD 340U
Chromatographic data system: Dell Optiplex GX 280 with Chromeleon
Vers. 6.70 from DIONEX
Stationary phase: Luna C18, 3µm from Phenomenex
Column dimension: 150 x 2.0 mm
with pre-column Luna C18, 3 µm

The following chromatographic conditions were used:
Injection volume: 25 µL or 100 µL
UV-detection: 3D Field, ¿ = 200 – 500 nm
Wavelenght (UV-VIS 1): 246 nm
Eluent A: 100 % water
Eluent B: 100 % acetonitrile
Flow rate: 0.35 mL/min
Gradient program: 0 min 100 % A and 0 % B
0:9 min 100 % A and 0 % B
2.5 min 40 % A and 60 % B
8.0 min 40 % A and 60 % B
9.5 min 0 % A and 100 % B
12.0 min 0 % A and 100 % B
12.5 min 100 % A and 0 % B
20.0 min 100 % A and 0 % B

Analytical monitoring:

yes

Details on sampling:

- Concentrations:
For Tier I tests, adsorption and desorption kinetics, a concentration of 200 µg/L was used.
Adsorption and desorption isotherms were determined at the concentrations 0.2 mg/L, 0.44 mg/L, 0.97 mg/L, 2.13 mg/L and 4.69 mg/L (nominal concentrations).

Details on matrix:

Refer to Table 1
- Soil preparation (e.g.: 2 mm sieved; air dried etc.):
The study was performed with air-dried soils. After drying they were mixed and sieved < 2 mm before the start of the experiments and analysed for particle size distribution (sand, silt, clay), pH-value in aqueous CaCl2-solution, organic carbon content (OC) and cation exchange capacity (CEC).

Details on test conditions:

TEST CONDITIONS
All tests were performed at 20 °C in an air-conditioned room in the dark.

TEST SOLUTIONS:
- Preparation:
Since the test item is relatively poorly soluble in aqueous solutions (35 mg/L at 20°C) and the application solutions for the highest two initial concentrations would exceed half the solubility of the test item, it was decided to prepare all test application solutions (= stock solutions) of Preventol A 6 in the organic solvent acetonitrile.
- Application:
For the different test item concentrations various volumes of the stock solution were spiked to the system consisting of soil and 0.01 M CaCl2 solution. The content of organic solvent in the aqueous phase did not exceed 0.1 %.

Computational methods:

The amount of test substance adsorbed to soil is calculated as the difference between the amount of test substance initially present in solution and the amount remaining at the end of the experiment (indirect method).
Calculations were performed by means of a commercially available computer program (Excel 2003) using up to fifteen decimal points.

Type:

Koc

Value:

>= 293 - <= 504

Temp.:

20 °C

Details on results (Batch equilibrium method):

The stability of Preventol A 6 during the tests was checked by HPLC-analysis of control samples and the mass balance. The mass balance tests showed recoveries of Diuron in the range of 90 % to 94 %. The results of the analysis of the control samples showed that there was no adsorption to the surface of the test vessels. The detected amount of Diuron in the control samples remained stable during the whole test period

Statistics:

Sorption tests with different concentrations of the test item (range from 100 to 5000 mg/L) and a soil/solution ratio of 1/50 were evaluated using the Freundlich equation
log Csads(eq) = KFads + 1/n * log Caqads (eq)
and linear regression analysis.

Results of the analysis show that Diuron remained stable for the test duration and that no adsorption to the surface of the test vessels occured

Sorption kinetics showed that equilibrium conditions were achieved after 48 h.

Results indicate that Diuron has a low potential to adsorb to soil considering the log K_oc is < 3 (determined value 2.5)

The desorption coefficients were higher than the adsorption coefficents.

The K_oc Values are summarised in the Tables below.

Adsorption: Linear regression analysis of the adsorption data of Diuron (Freundlich adsorption isotherm)

	RefeSol 01-A	RefeSol 03-G	RefeSol 05-G	RefeSol 06-A	Lufa 2.3
Correlation coefficient R^2	0.9959	0.9997	0.9987	0.9951	0.9930
Intercept of y-axis (log KF^ads)	0.6979	1.0976	1.0043	0.7892	0.6518
Slope (1/n)	0.7858	0.8431	0.8933	0.8354	0.6701
Adsorption coefficient KF^ads	4.99	12.52	10.10	6.15	4.48
Content of org. carbon Corg[%]	0.99	3.52	2.79	2.10	0.98
Normalized adsorption coeff. Koc^ads	504	356	362	293	458

Mean K_oc = 395 (log K_oc 2.5)

Desorption: Linear regression analysis of the adsorption data of Diuron (Freundlich adsorption isotherm)

	RefeSol 01-A	RefeSol 03-G	RefeSol 05-G	RefeSol 06-A	LUFA 2.3
Correlation coefficient R^2	0.9857	0.9974	0.9983	0.9969	0.9935
Intercept of y-axis (log KF^des)	0.8964	1.1909	1.0711	0.8900	0.9616
Slope (1/n)	0.8337	0.8314	0.9008	0.8125	0.7810
Desorption coefficient KF^des	7.88	15.52	11.78	7.76	9.15
Content of org. carbon Corg[%]	0.99	3.52	2.79	2.10	0.98
Normalized desorption coeff. Koc^des	796	441	422	370	934

Mean K_oc = 593

Executive summary:

An absorption/desorption test is available for this substance in accordance with the prevailing OECD guidelines (OECD 106), with GLP. The adsorption/desorption characteristics of 5 soils were investigated. The adsorption K_oc values ranged from 293 to 504 (Mean K_oc = 395 corresponding to a log K_oc = 2.5). The desorption K_oc values ranged from 370 to 934 (Mean K_oc = 593). The log K_oc of < 3 indicates that Diuron has a low potential to adsorb to soils as per the TGD.

Description of key information

The low log Koc value of diuron is 2.5.

Key value for chemical safety assessment

Koc at 20 °C:

395

Additional information

An absorption/desorption test is available for this substance in accordance with the prevailing OECD guidelines (OECD 106), with GLP. The adsorption/desorption characteristics of 5 soils were investigated. The adsorption K_oc values ranged from 293 to 504 (Mean K_oc = 395, corresponding to log K_oc of 2.5). The desorption Koc values ranged from 370 to 934 (Mean K_oc = 593) (Derz, 2009). The log K_oc value of 2.5 indicates that Diuron has a minor tendecy to leach.