INTENSE PULSED LIGHT FOR VINEYARD WASTEWATER: A PROMISING NEW PROCESS OF DEGRADATION FOR PESTICIDES

Abstract

The use of pesticides for vine growing is responsible for generating an important volume of wastewater. In 2009, 13 processes were authorized for wastewater treatment but they are expensive and the toxicological impact of the secondary metabolites that are formed is not clearly established. Recently photodecomposition processes have been studied and proved an effectiveness to degrade pesticides and to modify their structures (Maheswari et al., 2010, Lassale et al., 2014). In this field, Pulsed Light (PL) seems to be an interesting and efficient process (Baranda et al., 2017). Therefore, the aim of this work was to investigate the PL technology as a new process for the degradation of pesticides.

The degradation by PL with a LPBox (Sanodev) of 20 pesticides widely used in viticulture was studied by HPLC-MS/MS. Firstly, untargeted analyses were performed in order to observe secondary metabolites formed during PL treatments. This study allowed to detect 118 metabolites and 53 hypotheses of structures were proposed using m/z, isotopic patterns of the molecules containing halogens as well as results previously obtained in the literature. Then, a quantitative method was built for the 20 studied pesticides and for the compounds previously identified as secondary metabolites. Two transitions per compound were used following fragmentation experiments. The developed MRM method allows absolute quanti- fication of the parent molecules and relative quantification of 87 major secondary metabolites. In order to further study the degradation ability of LPBox on pesticides, 7 pesticides were selected because of their rapid degradation with PL. An optimization was made to identify the number of pulses needed to degrade the 7 pesticides. These experiments show that the different light rays produced by LPBox are able to degrade pesticides from their LC50 (Daphnia Magna) to a concentration lower than their limit of quantification (LOQ). These experiments also demonstrate that it is possible to relatively quantify secondary metabolites of pesticides after PL treatment. Real wastewater samples were also treated by PL showing effective degradation of pesticides.

In conclusion, our results proved that PL has an effective impact on all pesticides treated although the fluence needed is molecule-dependent. An optimization in terms of fluence showed that it was possible to degrade pesticides from a toxic concentration to a concentration below the LOQ.