Photo-Fenton decomposition of chlorfenvinphos: determination of reaction pathway

The purpose of this work was to determine the degradation products and pathway of chlorfenvinphos (CFVP) in water treated by photo-Fenton driven by solar irradiation, as well as to develop an analytical procedure for the degradation experiments. Degradation products and pathway were determined in a laboratory experimental setup. Routine water sample analysis was done by standard laboratory wet chemistry procedures and the use of laboratory equipment such as HPLC-UV and ionic chromatography (IC). Solid-phase extraction (SPE) was used to extract analytes from an aqueous matrix, and GC-MS was used to identify intermediate degradation products. The use of an HPLC-TOF-MS provided more results on degradation products and more insight was gained into how degradation takes place. In all experiments, strong mineralisation and degradation of CFVP was observed. CFVP and its degradation products, like 2,4-dichlorophenol, 2,4-dichlorobenzoic acid and triethylphosphate were decomposed into organic substances like acetate, formate, maleate, and inorganic ions like chloride and phosphate, within the detection limits (12.5 μg/L for CFVP in the GC-MS and 40 μg/L in HPLC-UV) of the equipment used. In fact, Cl⁻ emerges in nearly stoichiometric concentrations and PO₄³⁻ is precipitated as FePO₄. The remarkably complete absence of chlorinated aliphatic substances and chlorinated acids leads to the conclusion that chlorine is removed very quickly, and that residual DOC does not correspond to any chlorinated compound.