Photodegradation of profenofos in aqueous solution by vacuum ultraviolet

Profenofos is a widely used organophophorous pesticide for several crops and is detected in drinking water sources. This study investigated the degradation of profenofos using vacuum ultraviolet (VUV) compared with ultraviolet (UV). The factors affecting the degradation performance including pH, profenofos concentration, bicarbonate, nitrate, nitrite, natural organic matter (NOM), and aeration were examined. Profenofos removal efficiencies were 84 % and 52 % by VUV and UV after 7 min of irradiation, respectively (Initial profenofos concentration of 2 mg/L). Degradation of profenofos by VUV were 3 times faster than UV. The degradation rates decreased with increasing initial profenofos concentration. Direct photolysis at 185 nm and OH^• played major roles for profenofos removal by VUV. Aeration enhanced the profenofos degradation and mineralization by VUV but not UV. Bicarbonate inhibited the profenofos degradation while nitrate (≤50 mg-NO₃^-/L) acted as a photosensitizer enhancing profenofos degradation. NOM from groundwater and surface water sources also inhibited the profenofos removal by VUV as high as 39 % compared to deionized water. However, NOM promoted the profenofos removal by UV because degradation by OH^• formed via NOM photolysis became the main degradation mechanism. The result of profenofos degradation under isolated NOM fractions elucidated that hydrophobic fractions had less inhibition compared to hydrophilic fractions. Identified products suggested that the pathway of profenofos photodegradation was the breaking of the OP bond and reduction of Br.