Impact of a pulsed light process on phytosanitary products and ecotoxicity of viticultural wastewaters

Pulsed light (PL) treatment of three viticultural wastewaters (WWs) was performed with increasing fluence from 0 to 91 J/cm2. The evolution of the concentrations of the pesticides was monitored by High-Performance Liquid Chromatography coupled with tandem Mass Spectrometry (HPLC-MS/MS). PL enabled a significant decrease in concentration of the majority of the pesticides present in the wastewaters (WW): 6 out of 12 pesticides were degraded by 62 to 92 % in WW1, 7 out of 10 by over 80 % in WW2, and the only pesticide observed, fluopicolide, was degraded by 87 % in WW3. Only four pesticides were not significantly affected by PL: ametoctradin, benalaxyl, dimethomorph and tebuconazole. PL treatment was found to be less effective on wastewater than on pesticide-spiked deionised water, likely due to the wastewater matrix components absorbing the radiation. Fifteen of the 36 targeted photoproducts were observed following PL treatment of wastewater. The main potential reactions of the halogenated compounds were dehalogenation or substitution of halogen by hydroxyl groups. A photoproduct and possibly natural metabolite of fenbuconazole (m/z 303) was observed in an untreated sample. Acute toxicity tests were performed on the bacteria A. fischeri. A significant reduction in toxicity was observed in the three tested wastewaters: by a factor of 4.1, 6.5 and 4.3 in WWs 1, 2 and 3 respectively. However, the wastewaters remained highly toxic even after the highest fluence applied, probably due to very high copper concentrations in the three wastewaters, and to the absorbance of the samples reducing the degradation efficiency of the PL. Further studies should focus on adapting PL treatment to wastewater; the first step should be a pilot study performed on a semi-industrial scale. Toxicity analyses should be carried out on various freshwater trophic levels to ensure the harmlessness of the process.