Accelerated remediation of organochlorine pesticide-contaminated soils with phyto-Fenton approach: a field study

Phytoremediation and advanced oxidation processes are among the most promising techniques for removing organic pollutants from soils. A field trial was performed for six months to evaluate the effect of nano-Fe₃O₄ on the degradation of organochlorine pesticide residues including Lindane, p,p′-dichlorodiphenyltrichloroethane (DDT), p,p′-dichlorodiphenyldichloroethylene (DDE), and p,p′-dichlorodiphenyldichloroethane (DDD) in pesticide-contaminated soils in the presence of vetiver in Bac Giang province, Vietnam. Vetiver was planted in three zones with different nano-Fe₃O₄ concentrations. Soil samples from each zone were periodically collected to determine the remaining concentrations of selected organochlorine pesticides via gas chromatography–electron capture detector. Results indicated that the total DDT concentrations in the examined soil were 1.9–13 times higher than the permissible threshold level (10 µg g⁻¹) established by the national technical regulation on pesticide residues in soil. The (p,p′-DDE + p,p′-DDD)/p,p′-DDT ratios ranged from 13.5 to 114, indicating the absence of recent inputs of technical DDTs at the study area. DDT dechlorination mainly occurred under aerobic pathways to form DDE. Furthermore, DDE degradation in soil was adequately described by the pseudo-first-order kinetics model (R² > 0.892). In the presence of vetiver, the rate constants of DDE degradation were 0.264, 0.350, and 0.434 month⁻¹ with 0, 25, and 100 mg kg⁻¹ of added nano-Fe₃O₄, respectively, indicating that the degradation of DDE correlated positively with Fe₃O₄ concentration in the soil. Additionally, the presence of vetiver and nano-Fe₃O₄ in the soil increased DDT removal rates, which might be linked to the involvement of Fenton/Fenton-like reactions.