Temperature Dependent Adsorption-Desorption Behaviour of Pendimethalin in Punjab Soils.

This study shows the effect of soil type and temperature on the adsorption and desorption behaviour of pendimethalin using a batch equilibration technique. Adsorption kinetics followed pseudo-second-order-model (R2  > 0.99). The shape of adsorption curve for studied soils was S-type at 30 and 40°C and L-type at 50°C. The isotherms were nonlinear and were well described by Freundlich equation. Adsorption capacity ranged from 1.4 to 2.2 μg1 - 1/n  g-1  mL1/n and the order of adsorption was: clay loam > sandy loam > loamy sand indicating strong affinity of pendimethalin towards organic matter and clay content. Irrespective of soil type, the adsorption of pendimethalin increased with increase in temperature suggesting endothermic process. Freundlich desorption coefficient was greater than adsorption in all soils at studied temperatures indicating hysteresis. Thermodynamic parameters revealed spontaneous adsorption process which becomes more favourable at high temperature. The adsorption of pendimethalin was dominated by surface adsorption at lower equilibrium concentration and partition at high concentrations.