Sorption and Infiltration Potential of a Cationic Herbicide (Paraquat) in Three Cocoa Growing Soils in Nigeria

Abstract

Despite the ban of paraquat, its use among Nigerian farmers for weed control is still popular. Larger proportion of applied herbicide ends up in the soil matrix. Off-site transfer of the residual paraquat as contaminant to other environmental compartment depends on sorption process. In order to study the influence of soil characteristics on retention and infiltration of paraquat in cocoa soils, adsorption of paraquat in selected cocoa soils was carried out. In the course of the experiment, Owena, Ibadan and Ikom soils were equilibrated with paraquat solutions of different concentrations ranging from 100 to 800 mg paraquat kg-1 soil. Result showed that, Freundlich model gave better description of paraquat adsorption in the investigated soils than Langmuir model. The pseudo second order kinetic equation gave better description of the adsorption mechanism than pseudo first order. Statistical analysis showed that, aluminium oxide and clay mineral contents were the main soil physicochemical parameters that influenced paraquat sorption in the soils. The low values of groundwater ubiquity score obtained from the adsorption data showed that, the investigated soils were non leacher of paraquat. Hence, its guided and appropriate use may not cause underground water contamination.