Adsorption study of 14C-paraquat in two Malaysian agricultural soils

Abstract

The adsorption equilibrium time and effects of pH and concentration of 14C-labeled paraquat (1,1′-dimethyl-4,4′-bipyridylium dichloride) in two types of Malaysian soil were investigated. The soils used in the study were clay loam and clay soils from rice fields. Equilibrium studies of paraquat in a soil and pesticide solution were conducted. Adsorption equilibrium time was achieved within 2 h for both soil types. The amount of 14C-labeled paraquat adsorbed onto glass surfaces increased with increasing shaking time and remained constant after 10 h. It was found that paraquat adsorbed by the two soils was very similar: 51.73 (clay loam) and 51.59 μ g g-1 (clay) at 1 μ g/ml. The adsorption of paraquat onto both types of soil was higher at high pH, and adsorption decreased with decreasing pH. At pH 11, the amounts of 14C-labeled paraquat adsorbed onto the clay loam and clay soil samples were 4.08 and 4.05 μ g g -1, respectively, whereas at pH 2, the amounts adsorbed were 3.72 and 3.57 μ g g-1, respectively. Results also suggested that paraquat sorption by soil is concentration dependent. © 2010 Springer Science+Business Media B.V.