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Environmental fate & pathways

Adsorption / desorption

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In a soil adsorption/desorption study, the Freundlich adsorption coefficient (K) for MON 13900 ranged from 0.60 to 3.72, the adsorption distribution coefficient Kd from 0.64 to 5.16 and the adsorption coefficient as a function of organic carbon content (Koc) from 55.7 to 289.9 (log Koc: 1.74 to 2.46). These values suggest that MON 13900 has a low to moderate potential to adsorb to soil. 

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An adsorption/desorption (batch equilibrium) study was conducted to determine the leaching potential of MON 13900 and its aerobic soil metabolites in four different soils according to a company-internal protocol designed to satisfy US EPA Guideline 163-1. A mixture of MON 13900 and its aerobic soil metabolites was generated by aging aerobically14C-labelled test substance in Sarpy sandy loam soil for 30 d, then extracting with a solvent mixture. The soil extract was concentrated to remove organic solvent, then dosing solutions containing a mixture of the test substance and its aerobic soil metabolites were prepared. Four solution concentrations (0.050, 0.202, 0.603 and 0.945 ppm test substance equivalents) were used in the adsorption/desorption experiment. Portions of Drummer silt loam, sable silty day loam, sarpy sandy loam and spinks loamy sand were subjected to one adsorption step with each solution, followed by three desorption steps with fresh 0.01 M aqueous CaSO4 (5:1 solution:soil). Liquid scintillation counting was used to monitor concentrations. The distribution of MON 13900 and its metabolites in the solutions was determined where feasible by high performance liquid chromatography with radioactive flow detection. Adsorption distribution and Freundlich coefficients were calculated for each soil. The Freundlich adsorption coefficient (K) ranged from 0.79 to 3.50 for the MON 13900 and soil metabolite mixture, and from 0.60 to 3.72 for MON 13900 alone. The adsorption distribution coefficient (Kd) ranged from 0.82 to 4.40 for the test substance and soil metabolite mixture, and from 0.64 to 5.16 for the test substance alone. The adsorption coefficient as a function of organic carbon content (Koc) ranged from 71.3 to 247.2 for the test substance and soil metabolite mixture, and from 55.7 to 289.9 for the test substance alone. The results indicate that MON 13900 and its aerobic soil metabolites are moderately adsorbed to silt loam soils and poorly adsorbed to sandy loam and loamy sand soils. Desorption of test substance and its soil metabolites were essentially complete after three desorption cycles. These characteristics suggest that MON 13900 may have a potential for movement through soil.