Formation of chlorinated by-products during photo-Fenton degradation of pyrimethanil under saline conditions. Influence on toxicity and biodegradability

Abstract

This study evaluated the formation of chlorinated transformation products during photo-Fenton treatment of pyrimethanil (PYR-20mgL−1) in two water matrices, demineralised water (DW) and water containing 5gL−1 of NaCl (DWNaCl). All experiments were carried out in compound parabolic collectors (CPC) at an initial Fe2+ concentration of 5mgL−1 and H2O2 concentration of 150–350mgL−1. Dissolved Organic Carbon (DOC), High-Performance Liquid Chromatography with Diode-Array Detection (HPLC–DAD), Liquid Chromatography–Time-Of-Flight Mass Spectrometry (LC–TOF-MS), toxicity and biodegradability tests were conducted to control the photocatalytic treatment. In DW, PYR was completely eliminated after 11.8min of illumination and initial DOC was reduced 50% after 79min of illumination with 33mM of H2O2 consumed. On the other hand, in DWNaCl water matrix, the same reduction in DOC took 110min of illumination and H2O2 consumption of 39mM, and total degradation of PYR was observed at 12min of illumination. PYR transformation products (TPs) were identified by LC–TOF-MS. It was demonstrated that photo-Fenton in a DWNaCl produces some chlorinated TPs in addition to the non-chlorinated TPs identified during degradation in the DW. All TPs formed were eliminated during photo-Fenton. Additionally, the presence of chlorinated TPs does not increase the toxicity of the water, and TPs formed are more biodegradable than PYR.