Paraquat Dynamics on Western Andosolic and Ferrallitic Soils of Southern Cameroon

Phytosanitary products are frequently used by agriculture worldwide and in Cameroon in particular; this with a view to protecting crops and improving agricultural yields (Riba and Silvy, 1989; Bonny, 1996; Mattews et al., 2003). There are many studies on the retention of pesticides by soils, but in Cameroon, very few studies have focused on the interaction between andosols, ferralsols and the pesticides paraquat and carbendazim, which are widely used by farmers in Foumbot and Ebolowa. The objective of this work is to provide elements of understanding on the mobility of paraquat along the profile of andosolic soils of Foumbot and ferralitic soils of Ebolowa during which the soil samples were collected. The soil samples were characterized by the analytical method in accordance with the international standards at the Research Unit of Soil Analysis and Environmental Chemistry of the University of Dschang, as recommended by Pauwels et al. (1992). The different analyses of the soil samples were carried out according to the classical procedures of the Faculty of Agronomy and Agricultural Sciences, Soil, Plant and Water Laboratory. Statistical analysis was performed. Pearson correlation tests were performed to correlate soil physicochemical properties with soil adsorption parameters; thus, it has been observed that there is a strong correlation between the CEC and the rate of organic matter. The experimental device used for this study is a block device. This study was carried out in batch mode and by varying the contact time, the pH of the solution, the mass of the soil, the concentration of the solution. The physicochemical characterizations of the soils were studied. The mineralogical analysis was carried out by X-ray and infrared diffraction. The analysis of the samples was carried out by UV-Vis absorption spectrometry. The study of the adsorption kinetics showed that the adsorption of paraquat by the soils of Foumbot NK1, NK3 and Ebolowa MIN1 is better described by the pseudo-second order kinetic model since the q_e values obtained from this model are close to the experimental values. The study of the adsorption kinetics showed that the adsorption process is very fast during the first thirty minutes and medium to very slow afterwards. The half-reaction times indicate that the kinetics of pollutant accumulation is faster on the surface of fallow soil NK1 (t1/2 = 11.30 min.), followed by cultivated soil NK3 (t1/2 = 19.94 min.) and finally the bare ground of Ebolowa MIN1 (t1/2 = 264.05 min.). Three adsorption