Mitigation of Glyphosate Ecotoxicity by Vacuum-UV Treatment

Azole fungicides have a variety of different applications to prevent the spread of fungal diseases. They are widely used not only in agriculture to control diseases in crops and vineyards, but also in medicine to treat human diseases. Due to their widespread use and environmental persistence, azole fungicides are frequently detected in wastewater, surface water and occasionally in groundwater. Their bioavailability to aquatic organisms has raised concern about potentially adverse effects on non-targeted organisms. UV treatment has appeared as a promising technology to remove unwanted chemicals from the water cycle and can potentially mitigate environmental impacts. Vacuum-UV (VUV) irradiation of water results in the in situ generation of reactive species, mainly hydroxyl radicals, able to react with a wide range of chemical pollutants. In this study, we investigated the potential of VUV (185 nm) and UV-C (254 nm) irradiation to degrade the fungicides tebuconazole (pesticide) and clotrimazole (pharmaceutical) in water matrices. The effects of monochromatic UV-C irradiation were compared with simultaneous irradiation by UV-C and VUV. The degradation of tebuconazole and clotrimazole and the associated transformation pathways were elucidated by HPLC and LC-HRMS analysis. Changes in toxicity during different UV regimes were examined using aquatic organisms from different trophic levels. The test battery included the luminescent bacterium Aliivibrio fischeri, the bioluminescent yeast Saccharomyces cerevisiae BLYR, the fungus Fusarium graminearum, the freshwater microalgae Raphidocelis subcapitata, and the crustacean Daphnia magna. These organisms were used to assess biological effect before and after UV exposure of parent compounds and degradation products. UV-C and VUV irradiation significantly decreased concentrations of the parent compounds and decreased the ecotoxicity by increasing the apparent EC values. A direct positive correlation was observed between the disappearance of the parent compounds and the measured decreases in toxicity to the test organisms. UV-C and VUV treatment was able to alleviate the ecotoxicity of tebuconazole and clotrimazole at concentrations below and above the mg/L level. The study showed that bioassays can provide key information about changes in water chemistry during photodegradation experiments and that UV mediated photolysis of tebuconazole and clotrimazole can degrade these compounds and decrease the overall ecotoxicity.