Effect of Copper (II) on the Sorption/Desorption of Chlorsulfuron in Five Wheat Growing Regions of the Mara River Basin, Kenya

Aim: To study the effect of copper ions on the sorption and desorption of chlorsulfuron in five, wheat growing soils from Mara River Basin, Kenya.

Study Design: The experiments were laid down in a Completely Randomized Design (CRD) with three replications. Control experiments were carried out using soils without history of application of chlorsulfuron.

Place and Duration of Study: Department of Chemistry, Maseno University and Center of Analytics, Jülich Research Center from April 2014 to May 2015.

Methods: Adsorption of chlorsulfuron (0.625–15mgl−1) in the presence of Cu2+ (0, 50 and 100 mgl−1) was studied using batch sorption method. The data fitted well on the Freundlich adsorption equation. Fourier Transform Infrared (FTIR) analysis was done to one soil to show the mechanism of sorption on soil.

Results: Chlorsulfuron was sorbed on the soils with adsorption coefficients (Kf) ranging between 0.51 and 1.49. Increasing Cu2+ concentration increased the sorption of chlorsulfuron in all the five soils. This was possibly due to decreased equilibrium solution pH and formation of Cu-chlorsulfuron complexes which were preferentially sorbed via the carboxylic and hydroxylic functional groups of the soil. Moreover, Cu2+decreased hysteresis effects on desorption of chlorsulfuron.

Conclusions: The increase in sorption of chlorsulfuron in the presence of Cu2+ could suppress the bioactivity of the herbicide. However Cu2+ decreased hysteresis effects on desorption of chlorsulfuron implying that more of sorbed chlorsulfuron can be released to the soil solution. This will increase the leaching potential onto the lower profiles and surrounding aquatic systems.