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A Kinetic and Equilibrium Study of the Adsorption of Carbaryl and Parathion upon Soil Organic Matter Surfaces¹

ABSTRACT

Insight into the mechanisms of carbaryl (1-Napthyl-N-methyl carbamate) and parathion (O, O-Diethyl-o-p-nitrophenylphosphorothioate) adsorption upon organic matter derived from the Romney silty clay loam, Zanesville silt loam, and Carlisle muck soils was obtained by twofold kinetic and equilibrium study of adsorption in nonflow aqueous systems. The differences in adsorptive characteristics of the various types of organic matter were small in both the kinetic and equilibrium studies, but changing the saturating cation from calcium to hydrogen greatly increased the adsorptive capacities for both insecticides. The magnitude of the adsorptive capacities was explained in terms of the magnitude of the hydrophobic natures of the insecticide adsorbates and the organic matter adsorbents.

Kinetic adsorption studies conducted at 5, 25, and 40C showed the rate to increase as the temperature increased with the magnitude of the initial rate constant being 10^-4 sec ^-1. The rate-limiting step was interpreted to be diffusion of the insecticide solute molecules to the surface of the adsorbent for the first 10 min of adsorption. At longer times, intraparticle diffusion of the adsorbate into the interior of the adsorbent particles was rate limiting.

¹ Contribution from the Department of Agronomy, Purdue Agricultural Exp. Sta. (Journal Paper no. 4282, Lafayette, Ind. 47907.

² Former Graduate Assistant (now Research Hydrologist, US Geological Survey, Denver, Colo.), and Professor of Agronomy, Purdue University, respectively.

Received for publication January 4, 1971. Accepted for publication April 30, 1971.