Kinetic studies on the 2,4-D herbicide transport in small columns in the laboratory

The herbicide 2,4-D (2,4-Dicholorophenoxyacetic acid) is a growth plant regulator and an herbicide applied for general weed control. In this laboratory study, batch sorption and miscible displacement experiments were performed in three soils collected at different depths at the Serres de Pals golf course (Girona, Spain). The experiments were performed in two high-pressure steel iron columns of 10 em long and 2 cm of diameter. Sodium Pentafluorbenzoate (PFB was used as a conservative tracer. Measured batch sorption isotherms for 2,4-D conformed to the lineal model, and the very low values of the sorption coefficients suggest a high leaching potential of the compound. Pulse kinetic experiments for PFB and continuous flow experiments for 2,4-D were carried out. 2,4-D breakthrough curves (BTCs) measured in soil columns show symmetrical behaviour. The Brenner's equilibrium analytical model and a non-equilibrium with sorption and lineal degradation model were fitted to the breakthrough curves to estimate dispersivity (D), Peclet number (P) and the parameters for nonequilibrium sorption (beta,omega,xi,eta). Peclet number values indicate that dispersive flow dominates over diffusive flow, as it could be expected. Results of retardation factors from batch an kinetic experiments implies that the herbicide may leach under field conditions due to the low reactivity with the soil compounds.