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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:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study, GLP, analytical monitoring. Non-sterlised soil has been used although reaching an adsorption plateau was not proven and biodegradability has not been taken into account.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1995

Materials and methods

Test guideline
Qualifier:
according to
Guideline:
OECD Guideline 106 (Adsorption - Desorption Using a Batch Equilibrium Method)
GLP compliance:
yes
Type of method:
batch equilibrium method
Media:
soil

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Purity : 99.217 %
Impurities: 0.0005 % Methacrylic acid
0.012 % water
Inhibitor : 8 - 12 ppm Hydroquinone monomethyl ether

Study design

Test temperature:
20 +/- 2 deg C

Batch equilibrium or other method

Analytical monitoring:
yes
Details on sampling:
- Concentrations: 50:1, 65:1, 52:1 solution to soil ratio; Theoretcial concentration 4.95 mg/L
- Sampling interval: no data
- Sample storage before analysis: no data
Details on matrix:
COLLECTION AND STORAGE
- Geographic location: agricultural research sites or private gardens in Arkansas, Kansas and Washington
- Storage conditions: room temperature in plastic bags
- Soil preparation (e.g.: 2 mm sieved; air dried etc.): sieved through 2-mm screen


PROPERTIES
Arkansas
- Soil texture- Loam
- % sand: 35
- % silt: 48
- % clay: 17
- pH: 5.8
- Organic carbon (%): 0.88
- CEC (meq/100 g): 8.7
- Extractable Cations (Ca, Mg, Na, K, H) (ppm): Ca- 700; Mg- 120; Na- 65; K- 84; H- 37


Kansas
- Soil texture- Silty clay loam
- % sand: 11
- % silt: 58
- % clay: 31
- pH: 6.0
- Organic carbon (%): 1.8
- CEC (meq/100 g): 21
- Extractable Cations (Ca, Mg, Na, K, H) (ppm): Ca- 2600; Mg- 330; Na- 34; K-109; H- 48


Washington
- Soil texture- Sandy loam
- % sand: 47
- % silt: 46
- % clay: 7
- pH: 7.7
- Organic carbon (%): 0.71
- CEC (meq/100 g): 13.4
- Extractable Cations (Ca, Mg, Na, K, H) (ppm): Ca- 1800; Mg- 210; Na- 24; K- 419; H- 14
Details on test conditions:
Soil sorption and desorption:
A screening test was performed in duplicate for Arkansas loam, Kansas silty loam and Washington sandy loam
using 0.01 M CaCl2 with respective solution:soil ratios of 50:1, 65:1 and 52:1.
An adsorption phase was conducted, followed by two subsequent desorption phases (16 hours per phase).
The sorption coefficients Kd and Koc calculated from the aqueous solution concentrations measured in the
sorption phase.
Computational methods:
The percent of test material sorbed was calcualted as
A = 100 x (G-Ce) x V0/GV0 = 100 x X/G

The percent of test material which was desorbed was calculated as
D = 100 x (C1xVe) + (C2xV0) - (V0-Ve)Ce/X

m = dry weight of soil (g)
Ce = concentration of test material remaining in solution in the sorption step (mg/L)
C1 = concentration of test amterial in solution in the first wash (mg/L)
C2 = concentration of test material in solution in the second wash (mg/L)
V0 = original volume of solution (mL)
Ve = volume of solution obtained after the sorption step (mL)
G = quantity of test material recovered from the soil-less control (mg/L)
%OC = percent organic carbon in the soil

The distribution sorption coefficient was determined using the following equation
Kd = X/m/Ce

X/m = concentration of test material in soil as ug/g
Ce = concentration of test material in the water phase as ug/mL

The sorption coefficient was also calculated as a function of the organic carbon content of the soil as

Koc = Kd x 100/%OC

Results and discussion

Adsorption coefficient
Type:
Koc
Value:
2 767
Remarks on result:
other: (geometric mean of 3 soils)

Results: Batch equilibrium or other method

Adsorption and desorption constants:
The average percent sorbed was 20.5, 49.6 and 34.5 % for Arkansas, Kansas and Washington soil, respectively.
Subsequent percent desorption could not be calculated because the aqueous concentrations were below the detection
limit of 0.0242 mg/L. The Kd estimates averaged 13.1, 64.5, 27.6; the corresponding Koc values averaged 1,480, 3,650 and
3,920, respectively.
Concentration of test substance at end of adsorption equilibration period:
The measured concentration of the test solutions was 4.06 mg/L. The concentration of the solution in the soul-less controls was 4.02 mg/L
Concentration of test substance at end of desorption equilibration period:
Subsequent percent desorption could not be calculated because the aqueous concentrations were below the detection limit of 0.0242 mg/L
Details on results (Batch equilibrium method):
The measured test solution concentrations prior to equilibration were 4.09 mg/L for the 5:1 solution:soil ratio solutions, 4.39 mg/L for the 50:1 and 100:1 solution:soil ratio solutions and 3.07 mg/L for the 200:1 solution:soil ratio solutions. Following 16 hours of equilibration for the initial preliminary test with the 5:1 solution to soil ratio, a percent sored could not be calculated due to excessive binding of test material in the aqeuous phase. After the 16-hour agitation period, the soil-less controls were observed to be clear and colorless. After centrifuging, the test replicates at the 5:1 solution:soil ratio were also clear and colorless with a moderate amount of organic plant matter floating on the surface of the solutions. High-speed centrifugation removed this material.
Additional preliminary testing, conducted at solution:soil ratios of 50:1, 100:1 and 200:1, had soil-less control concentrations of 4.71, 4.71 and 3.39 mg/L, respectively. The test replicates were observed to be clear and colorless with no organic plant matter floating on the surface of the solutions.

The screening test provided the sorption coefficients calculated from the aqueous solution concentrations measured in the sorption phase. The measured concentration of the test solutions was 4.06 mg/L. The concentration of the solution in the soil-less controls was 4.02 mg/L.

The average percent sorbed for the screening test was 20.5, 49.6 and 34.5% for the Arkansas, Kansas and Washington soil, respectively. Subsequent percent desorption could not be calculated because the aqueous concentrations were below the detection limit of 0.0242 mg/L. The resultant Kd estimates averaged 13.1, 64.5, 27.6; the corresponding Koc values averaged 1,480, 3,650 and 3,920, respectively.
After adsorption, all test material and blank replicates were observed to be clear and colorless. The Arkansas replicates had no observed organic matter floating on the surface and the Washington replicates had a moderate amount of organic plant matter floating on the surface of the solutions. After desorption, the Arkansas, Kansas and Washington test material samples were clear and colorless.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
In a valid guideline study the test substance was considered to be tightly bound to loam, silty clay loam and sandy loam tested. The corresponding Koc values averaged 1,480, 3,650 and 3,920.
Executive summary:

In a valid guideline study the test substance was considered to be tightly bound to loam, silty clay loam and sandy loam tested. The corresponding Koc values averaged 1,480, 3,650 and 3,920.

It should be recognised that when interpreting the measured data of this study that they had assumed binding to soil since they could not detect iBMA in the aqueous desorption phase. However, they failed to use sterilised soil and therefore rapid biodegradationby soil microflora may have contributed to the disappearance of iBMA from the aqueous phase and the true Koc is likely to be lower than that assumed.