Avermectin A1a, 25-cyclohexyl-5-O-demethyl-25-de(1-methylpropyl)-

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:

From 28 Jun 1989 to 25 Sep 1992

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: Study run to a method comparable with current guidelines and to GLP.

Qualifier:

according to guideline

Guideline:

other: U.S. FDA Technical Assistance Document 3.08

Deviations:

no

GLP compliance:

yes

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Test temperature:

21.1±0.6 ℃

Analytical monitoring:

not specified

Details on matrix:

PROPERTIES
Mississippi Silty Clay Loam (MSCY)
-Source: Mississippi
- Soil texture: Silty Clay Loam
- % sand: 5.0
- % silt: 64.0
- % clay: 31.0
- pH: 5.1
- Organic matter (%): 1.1
- CEC (meq/100 g): 7.3
- Exchangeable Cations (ppm): Phosphorus: 3; Potassium: 132; Magnesium: 305; Calcium: 320; Sodium: 11

California Clay Loam (CACY)
-Source: California
- Soil texture: Clay Loam
- % sand: 32.0
- % silt: 28.0
- % clay: 40.0
- pH: 7.3
- Organic matter (%): 3.0
- CEC (meq/100 g): 19.4
- Exchangeable Cations (ppm): Phosphorus: 103; Potassium: 999; Magnesium: 700; Calcium: 2160; Sodium: 43

Texas Silty Clay Loam (TXCY)
-Source: Texas
- Soil texture: Silty Clay Loam
- % sand: 13.0
- % silt: 59.0
- % clay: 28.0
- pH: 7.8
- Organic matter (%): 1.6
- CEC (meq/100 g): 15.0
- Exchangeable Cations (ppm): Phosphorus: 2; Potassium: 239; Magnesium: 1780; Calcium: 2580; Sodium: 11

Details on test conditions:

Test Solutions:
Equilibrating solutions for the screening and definitive tests were prepared by the direct addition of test substance to the appropriate aqueous phase (0.01 M CaCl2 or distilled deionized water) in order to provide nominal concentrations of 10.0 μg/L for the screening test and 10.0, 5.0, 2.50 and 1.00 μg/L for the advanced test.

Test System:
Prior to test initiation, the propensity for the test substance to adhere to teflon and glassware at low concentrations was observed. Various types of pretreatment were performed and the following procedure was used to rinse each test vessel for each phase of testing prior to use. Vessels were rinsed several times with alcoholic potassium hydroxide, DI water, 10% nitric acid and finally with DI water. All glass test vessels, pipets and graduated cylinders used during the study were subject to pretreatment.
Each test system for this study consisted of one 1 L amber glass bottles (MSCY), one 50 mL (TXCY) or one 200 mL (CACY) glass centrifuge tube with a teflon lined cap. Each contained soil, 0.01 M CaCl2 or deionized (DI) water, and the test substance as required per test. Individual test systems were identified by project number, soil type, replicate, concentration and for the equilibrium phase of the advanced test, agitation duration. All test systems were gently shaken for the necessary period using a LabLine Orbital Shaker, Model #3590. Test containers were wrapped in foil while being agitated to preclude photolysis of the test material.

Advannced Equilibrium Test:
The equilibrium phase test was performed with each soil type at a nominal concentration of 10.0 μg/L and a solution:soil ratio of 1000:1 for MSCY (this ratio was selected based on criteria published by ASTM), 200:1 for CACY and 80:1 for TXCY as determined from the screening tes. Equilibration periods of 2, 4, 8, 24 and 48 hours were used for the CACY and TXCY tests, and the MSCY test was also sampled at 72, 120, 144, 168 and 288 hours.

Advanced Isotherm Test:
For each soil type, the sorption phase of the advanced test was performed at the same solution:soil ratio as was used during the equilibrium phase test for an equilibration period of 72 hours for the MSCY test, 4 hours for the CACY test and 24 hours for the TXCY test, as determined from the equilibrium test. Nominal solution concentrations of 10.0, 5.00, 2.50 and 1.00 μg/L were prepared by direct addition of test substance to 0.01 M CaCl2.

Computational methods:

- Freundlich adsorption and desorption coefficients: Kd=(x/m)/C, where: x/m=concentration of the test substance in soil as μg/g; C=concentration of test substance in the water phase as μg/mL.

- Adsorption coefficient per organic carbon (Koc): Koc=(Kd x100) / % organic carbon, where the organic carbon content was calculated by dividing the percent organic matter by 1.7. The published literature (Black, et al., 1965) describes this procedure for converting between organic carbon and organic matter.

Type:

Koc

Value:

86 900

Temp.:

21.1 °C

Remarks on result:

other: MSCY

Type:

Koc

Value:

13 300

Temp.:

21.1 °C

Remarks on result:

other: CACY

Type:

Koc

Value:

7 520

Temp.:

21.1 °C

Remarks on result:

other: TXCY

Type:

log Koc

Value:

4.9

Temp.:

21.1 °C

Remarks on result:

other: MSCY

Type:

log Koc

Value:

4.1

Temp.:

21.1 °C

Remarks on result:

other: CACY

Type:

log Koc

Value:

3.9

Temp.:

21.1 °C

Remarks on result:

other: TXCY

Details on results (Batch equilibrium method):

The preliminary test results with CaCl2, which was tested at a mean measured concentration of 10.4 μg/L, resulted in a remaining average aqueous concentration of 0.880 ± 0.288 μg/L. The preliminary test results with DDI H2O, which was tested at a mean measured concentration of 9.9 μg/L, resulted in a remaining average aqueous concentration of 1.04 ± 0.939 μg/L. The preliminary test results were satisfactory and reproducible.
Results of the screening test showed that the presence of CaCl2 did not significantly interfere with the sorption of test substance to soil, as compared to the sorption in distilled deionized water. The degree of sorption indicated that the advanced tests should be conducted, at solution:soil ratios of 1000:1 for MSCY, 200:1 for CACY, and 80:1 for TXCY.
Equilibrium was reached after 72 hours with MSCY soil, after 4 hours with CACY soil and after 24 hours with TXCY soil.
The advanced isotherm test results indicated that the test substance readily sorbed onto all three soils; an average of 61% of the initial test substance added sorbed on to MSCY, an average of 68% sorbed onto CACY and an average of 64% sorbed onto TXCY.

Validity criteria fulfilled:

yes

Conclusions:

The results of this study indicate that the test substance sorption and desorption characteristics do not vary significantly among the three soil types. The LogKoc values are 4.9, 4.1 and 3.9 for MSCY, CACY and TXCY soil respectively at 21℃.

Description of key information

The LogKoc values are 4.9, 4.1 and 3.9 for MSCY, CACY and TXCY soil respectively at 21℃.

Additional information

An adsorption/desorption study was conducted on three soils according to FDA Technical Assistance Document 3.08 under GLP (Smith, 1992).

The results of this study indicate that the test substance sorption and desorption characteristics do not vary significantly among the three soil types. The LogKoc values are 4.9, 4.1 and 3.9 for MSCY, CACY and TXCY soil respectively at 21℃.