Remediation of soils polluted with difenoconazole, triadimenol and tebuconazole and their transformation products by persulfate at different scales

Soil pollution caused by pesticides has drawn increasing interest among the scientific community in the last decades. Persulfate is a promising oxidant applied to remediate pollutant-contaminated soils thanks to its high versatility and efficacy. In this study, a sulfate radical-based advanced oxidation process using persulfate was examined for degrading residues of three triazole fungicides (difenoconazole, triadimenol and tebuconazole) in soils at different scales (lab and field conditions). The influence of the initial concentration of persulfate, moisture, soil type and fungicides residence time in soil was evaluated. The results obtained at lab conditions showed that persulfate photo-oxidation under natural sunlight enhanced pesticide degradation rates in comparison with persulfate in darkness, photolysis and control (non-treated soil under sunlight and in darkness). The scavenger test allowed to identify hydroxyl ( • OH) and sulphate (SO 4 •- ) radicals as the main active species involved in solar persulfate-based treatment. Degradation increase was higher in freshly contaminated soils and in soils with a lower content of organic matter. Similar behaviour was observed in the treatments carried out at field conditions covering the soil container with a transparent polyethylene film (soil solarization inside and outside the greenhouse), such as a new activation method of persulfate. The formation of 26 transformation products during persulfate soil remediation treatments was also evaluated and degradation pathway for each fungicide was tentatively proposed. Therefore, this technology could be an efficient and promising tool to remediate soils contaminated with residues of pesticides in Mediterranean areas.