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Environmental fate & pathways

Adsorption / desorption

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Administrative data

Endpoint:
adsorption / desorption: screening
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1985
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1985

Materials and methods

Test guideline
Qualifier:
equivalent or similar to guideline
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
Version / remarks:
2000
Deviations:
no
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil

Test material

Constituent 1
Chemical structure
Reference substance name:
Ammonium 2-amino-4-(hydroxymethylphosphinyl)butyrate
EC Number:
278-636-5
EC Name:
Ammonium 2-amino-4-(hydroxymethylphosphinyl)butyrate
Cas Number:
77182-82-2
Molecular formula:
C5H12NO4P.H3N
IUPAC Name:
ammonium 2-amino-4-(hydroxymethylphosphinyl)butyrate
Radiolabelling:
yes

Study design

Test temperature:
22 °C

HPLC method

Details on study design: HPLC method:
The following HPLC condition was used for all analysis:

Stationary phase: Strongly basic anion exchanger on silica basis, Nucleosil SB5. Macherey und Nagel, FRG.
Column 125 mm x 4.6 mm
Eluent sodium sulfate solution c(Na2SO4) = 0.05 mol/L in water
Flow rate 1.0 mL/min
Injection volume 20 µL
Detection A UV-absorption at 199 nm
B Radioactivity detection
Cell volume: 200 µL
Scintillator: GT 200
Time const.: 5 s

Batch equilibrium or other method

Analytical monitoring:
yes
Details on sampling:
- Concentrations: 0.4, 0.8 , 2.0 and 4 mg/L

- Sample method: For the analysis of soil samples 3 aliquots of approx. 120 mg of each sample of dried soil (16h, 100°C) were weighed out and the radioactivity was determined in a Tricarb-Sample-Oxidizer. In this apparatus the evolved -14CO2 is trapped by 8 mL Carbo-Sorb and mixed with 12 mL of scintillation cocktail. This solution was measured in the liquid scintillation counter.

- Sampling interval: 2 / 4 / 8 / 16 / 32 / 48 / 72 h

- Sample storage: No storage documented
Matrix propertiesopen allclose all
Matrix no.:
#1
Matrix type:
silt loam
% Clay:
18.2
% Silt:
73.1
% Sand:
8.7
% Org. carbon:
0.99
pH:
5.9
CEC:
16.1 meq/100 g soil d.w.
Matrix no.:
#2
Matrix type:
silt loam
% Clay:
7.6
% Silt:
64.6
% Sand:
27.8
% Org. carbon:
0.63
pH:
6.4
CEC:
8.05 meq/100 g soil d.w.
Matrix no.:
#3
Matrix type:
sand
% Clay:
3.3
% Silt:
4.2
% Sand:
92.5
% Org. carbon:
0.85
pH:
6.8
CEC:
3.01 meq/100 g soil d.w.
Matrix no.:
#4
Matrix type:
other: Volcanic ash
% Clay:
46.1
% Silt:
30.6
% Sand:
23.3
% Org. carbon:
4.3
pH:
5.8
CEC:
18.3 meq/100 g soil d.w.
Details on matrix:
MATRIX #1:
Sampling site: American Hoechst Corp., Mississippi Research Farm, USA
% Water Content: 1.7

MATRIX #2:
Sampling site: Leland, MS 3756 USA
% Water Content: 0.2

MATRIX #3:
Sampling site: LTJFA-Speyer, Obere Langgasse 40, D-6720 Speyer, Germany
% Water Content: 0.4

MATRIX #4:
Sampling site: University of Tsukuba, Sahura-Tennodai, 1-1-1,Niikari-gun Ibarahi-hen, 305 Japan
% Water Content: 7.8
Details on test conditions:
TEST CONDITIONS
Test Solutions:
A stock solution of radiolabelled ammonium glyphosinate was prepared by adding an exactly equimolar amount of ammonia solution to 38.55 mg of the free acid of glyphosinate. The resulting solution was then transferred into a 50 ml volumetric flask and filled to the mark with bidistilled water. 5 ml of this solution were then added to 1 L aqueous CaCl2- solution. Solutions with a lower concentration of Hoe 039866 were obtained by further dilution with aqueous CaCl2-solution.

TEST SYSTEM
Adsorption equilibrium test:
50 ml of the aqueous solution of the radiolabelled active ingredient were then added with a pipette to the soil, the flask closed with a glass stopper and for equilibration stored in a thermostated water bath with shaking mechanism.
For the adsorption/desorption experiment prior to analysis the exact volume of the aqueous phase separated from the soil was measured using a 50 ml graduated cylinder and the soil filled back into the Erlenmeyer flask and equilibrated again with 50 ml of aqueous CaCl2-solution. After equilibration phases were again separated, the aqueous phase was analyzed and the whole procedure repeated. After the second desorption step aliquots of the soil were taken and the remaining radioactivity was determined after combustion.
The concentration of the active ingredient in the aqueous solution was always given in mg/L respectively mol/L. For simplification, these values were used equal to the concentrations in mg/kg resp. mol/kg when calculating adsorption coefficients and isotherms. This seems acceptable, since density of the 0.01 mol/L CaCl2- solution is in very good approximation equal to unity and the resulting error several orders of magnitude smaller than the analytical errors. Dimensionless K-values calculated in this way are identical to K-values in the dimension [ml/g].
Isotherms were determined from the molar concentrations in soil and aqueous phase according to the Freundlich equation.
Adsorption isotherms were determined for each soil by conducting adsorption experiments with the 4 different initial concentrations of the active ingredient in the aqueous phase(0.4, 0.8 , 2.0 and 4 mg/L nominal concentration).

Results and discussion

Adsorption coefficientopen allclose all
Sample No.:
#1
Type:
Koc
Value:
253 L/kg
pH:
5.9
Temp.:
22 °C
Matrix:
Silt Loam - I
% Org. carbon:
0.99
Sample No.:
#1
Type:
Kd
Value:
3.48 L/kg
pH:
5.9
Temp.:
22 °C
Matrix:
Silt Loam - I
% Org. carbon:
0.99
Sample No.:
#2
Type:
Koc
Value:
156 L/kg
pH:
6.4
Temp.:
22 °C
Matrix:
Silt Loam - II
% Org. carbon:
0.63
Sample No.:
#2
Type:
Kd
Value:
0.98 L/kg
pH:
6.4
Temp.:
20 °C
Matrix:
Silt Loam - II
% Org. carbon:
0.63
Key result
Sample No.:
#3
Type:
Koc
Value:
9.6 L/kg
pH:
6.8
Temp.:
22 °C
Matrix:
Sand
% Org. carbon:
0.85
Key result
Sample No.:
#3
Type:
Kd
Value:
0.08 L/kg
pH:
6.8
Temp.:
22 °C
Matrix:
Sand
% Org. carbon:
0.85
Sample No.:
#4
Type:
Koc
Value:
1 229 L/kg
pH:
5.8
Temp.:
22 °C
Matrix:
Volcanic ash
% Org. carbon:
4.3
Sample No.:
#4
Type:
Kd
Value:
52.85 L/kg
pH:
5.8
Temp.:
22 °C
Matrix:
Volcanic ash
% Org. carbon:
4.3

Results: Batch equilibrium or other method

Transformation products:
yes
Details on results (Batch equilibrium method):
Adsorption isotherms
Adsorption isotherms were determined for each soil by conducting adsorption experiments with 4 different initial concentrations of the active ingredient in the aqueous phase. The ratio of the different concentrations was approximately 1 : 2 : 5 : 10. The adsorption isotherms are graphically represented as logarithmic plots of the molar concentration of the active ingredient adsorbed on soil as a function of the molar concentration of the substance in the aqueous phase. From the figures as well as from the numerical data can be seen, that the adsorption isotherms for the soils No. I, II and IV are very well represented by the Freundlich-equation. Correlation coefficients r2 are 0.9996 for soil I, 0.9774 for soil II and 0.9998 for soil IV. Soil III shows a very bad correlation of the concentration of a. i. adsorbed on soil to concentration of the substance in the aqueous phase (r2 = 0.5933). This is certainly due to the very low adsorption of the substance on this soil (K — approx. 0.2), which does not allow a sufficiently precise determination of the decrease in the concentration of the test substance in the aqueous phase (less than 5 % of the initial concentration).

Adsorption – desorption behaviour
In addition to the adsorption experiment, desorption experiments were carried out with soils No. I, II and IV. Soil III was excluded, since the very low adsorption (less 5 %, see 5.2) made the determination impossible. The experiments show, that the distribution behaviour of Hoe 039866 between soil and water is not completely reversible. The adsorption coefficient, when determined by desorption, is generally higher than by adsorption. The total radioactivity remaining in the soil after 2 desorption steps is determined by combustion (see 4.5.2.3) and a mass balance calculated which accounts for approximately 90 % of the total radioactivity.

Any other information on results incl. tables

Besides the dependence of adsorption from the organic carbon, adsorption seems to be dependent from the clay content, respectively the ion exchange capacity of the soil, but the experimental data do not allow a quantitative calculation of the influence of these different parameters. Desorption data show, that the distribution of the compound between soil and water is not completely reversible, with coefficients determined by desorption from the soil about 2 to 10 times higher than those determined by adsorption out of the aqueous phase. Adsorption isotherms can be well described by the Freundlich equation. The adsorption kinetic was determined for the volcanic ash type of soil and showed no further decrease in the substance content of the aqueous phase after 48 h. No metabolite of the compound was detectable for incubation times up to 72 h.

Applicant's summary and conclusion