Degradation of chlorfenvinphos in water by photo-fenton : determination of reaction pathway

Abstract

The aim of this work was to determine the degradation pathway and degradation products of chlorfenvinphos (CFVP) in water by photo-Fenton process (Fe2+, H2O2, UV) as well as to develop an analytical procedure for the degradation experiments.The determination of the degradation products and pathway was achieved by operating the solar photocatalytic pilot plant at the Plataforma Solar de Almería (Spain), and generating an experimental setup for laboratory experiments. The routine analysis of water samples was achieved by standard laboratory wet chemistry procedures and the use of laboratory equipment such as HPLC-UV, IC, DOC, and UV-VIS-spectrometry. Solid Phase Extraction (SPE) was used to extract analytes out of a watery matrix and GC-MS was used to identify intermediate degradation products. The use of a HPLC-MS/TOF provided more results concerning the degradation products and more insight was gained how the degradation could take place. One of the main problems encountered was the non-selective, parallel reaction of OH· radicals with CFVP and its degradation products (DPs), so that no explicit degradation pathway could be developed. The detected substances were chlorinated aromatic acids,aldehydes, esters and phenols. Only 3 substances were identified which resembled to the original molecular structure of CFVP. The total absence of chlorinated aliphatic and the scarce appearance of monochlorided aromatic substances led to the conclusion that chlorine is substituted fast and irreversible. Some of the analysed substances could only be generated through additional transfer of ethoxy and hydroxyl radicals.In all experiments CFVP and its degradation products were decomposed under the detection limit (12,5ppb for CFVP in the GC-MS and 40 ppb in HPLC-UV) of the used equipment into harmless organic substances.