Comparative studies of various iron-mediated oxidative systems for the photochemical degradation of endosulfan in aqueous solution

• Photoactivation of Fe led to a faster removal of endosulfan than direct photolysis.
• UV/HSO5−/Fe2+ was the most efficient and economical among all the studied AOPs.
• Impact of initial concentration of peroxide and Fe2+ on degradation was explored.
• Potential degradation pathways and stereochemistry of endosulfan was explored.
• Main by-product endosulfan ether was formed and further degraded.

This study investigated iron-mediated oxidative processes for the photochemical degradation of endosulfan, a chlorinated insecticide and central nervous system disruptor. At UV fluence of 360 mJ/cm2, 52.4% and 32.0% removal of 2.45 μM initial endosulfan was observed by UV/Fe3+ and UV/Fe2+ processes, respectively, at an initial concentration of 17.8 μM iron. The degradation of endosulfan by UV/Fe3+ or UV/Fe2+ was dramatically enhanced by adding peroxide (i.e., H2O2, S2O82− or HSO5−). Among the UV/peroxide/Fe processes, the highest degradation efficiency of 99.0% at UV fluence of 360 mJ/cm2 was observed by UV/HSO5−/Fe2+ with 2.45 μM [endosulfan]0, 17.8 μM [Fe2+]0, and 49.0 μM [HSO5−]0. The observed degradation rate constant of endosulfan was promoted either by increasing [Fe2+]0 and/or [peroxide]0 or by decreasing [endosulfan]0, while the initial degradation rate of endosulfan increased with increasing [Fe2+]0, [peroxide]0, or [endosulfan]0. At UV fluence of 6000 mJ/cm2, 45.0% mineralization as represented by the decrease in total organic carbon content was observed by UV/HSO5−/Fe2+ at 9.80 μM [endosulfan]0, 980 μM [HSO5−]0, and 17.8 μM [Fe2+]0. The major by-product of endosulfan was observed in all cases to be endosulfan ether which was further degraded with an extended reaction time. The results suggest that iron-mediated advanced oxidation processes (AOPs) have a high potential for the removal of endosulfan and its by-product from contaminated water.

Figure optionsDownload as PowerPoint slide