Photocatalytic degradation of bentazone in soil washing wastes containing alkylpolyoxyethylene surfactants

Three alkylpolyoxyethylene surfactants bearing the same hydrophobic chain and a different number of oxyethylene groups were investigated as suitable candidates for the soil washing treatment of contaminated soil samples containing bentazone. Comparable good recoveries of the pesticide were obtained working with these surfactants. The photocatalytic treatment of the collected washing wastes, performed in the presence of suspended TiO2 particles under irradiation with simulated sunlight, leads to the effective degradation of bentazone residues after a time depending on the nature and concentration of the chosen amphiphile. Brij 35 was found to be the best surfactant candidate, giving the faster abatement of the pesticide in the collected wastes. The overall treatment time depends on the bentazone mineralization kinetics, markedly slow in the presence of surfactants. Useful information about the photocatalytic degradation route was obtained from the HPLC–MS analysis of transient intermediates formed in water.

► Washing with nonionic surfactants allows to extract bentazone residues from soil.
► Effective photocatalytic degradation of bentazone is achieved in the washing wastes.
► The pesticide degradation rate is higher using the more hydrophilic surfactant.
► A marked inhibition of bentazone mineralization is observed during the treatment.
► Three main transient intermediates are evidenced in water using HPLC–MS.