Kinetic and mechanism investigation on the gamma irradiation induced degradation of endosulfan sulfate

• Removal of endosulfan sulfate was assessed by gamma-rays under different conditions.
• Removal of endosulfan sulfate by gamma-rays was mainly due to aqueous electron.
• Removal of endosulfan sulfate was significantly affected by pH of aqueous solution.
• Second-order rate constants of endosulfan sulfate with hydroxyl radical and aqueous electron were determined.
• Degradation pathways of endosulfan sulfate were proposed from the nature of by-products evolved.

The gamma irradiation was investigated for potential removal of endosulfan sulfate, an emerging water pollutant and central nervous system disruptor. A removal efficiency of 99.5% of initially 1.30 μM endosulfan sulfate was observed at an absorbed dose of 1020 Gy. Aqueous electron (eaq−) was found to play primary role in the removal of endosulfan sulfate which was possibly due to greater reactivity of eaq− with endosulfan sulfate, considering the second-order rate constant of 8.1 × 109 and 3.4 × 1010 M−1 s−1 for hydroxyl radical (OH) and eaq−, respectively, with endosulfan sulfate. The removal efficiency of endosulfan sulfate was affected by the pH of aqueous solution, with observed removal efficiency of 99.5%, 98.3% and 31.3% at pH 6.2, pH 10.0, and pH 2.6, respectively. The efficiency was also influenced by inorganic anions and humic acid in the order of nitrate > nitrite > bicarbonate > carbonate ≃ humic acid. The initial degradation rate increased while degradation constant decreased with increasing initial concentrations of endosulfan sulfate. The degradation pathways showed that oxidative pathway was initiated at the SO2 bond while reductive pathways at the chlorine attached to the ring of endosulfan sulfate. The mass balance showed removal of 98% chloride and 72% sulfate ions from endosulfan sulfate at an absorbed dose of 1020 Gy. The removal of endosulfan sulfate followed by subsequent loss of by-products under extended treatment showed that gamma irradiation is potential technique for the remediation of organic pollutants from a water environment.