Degradation of atrazine in soil by dielectric barrier discharge plasma - Potential singlet oxygen mediation

Dielectric barrier discharge (DBD) was used for the first time to remediate atrazine-polluted soil in a plane-to-grid plasma reactor operating with air at atmospheric pressure. It was established that atrazine degradation efficiency is an increasing function of applied voltage and discharge frequency. The degradation efficiency of atrazine in dry soil reached as high as 86.9% and 98.1% after 60 min of plasma treatment, starting from initial pollutant concentrations of 100 and 10 mg/kg, respectively. Low soil moisture content (5-10%) was found to enhance atrazine degradation in the DBD reactor in comparison to dry soil conditions. Atrazine mineralization after 60 min of treatment was 65.5% as confirmed by total organic carbon (TOC) analysis. The degradation profile of atrazine under DBD treatment was assessed using Fourier transform infrared spectroscopy (FTIR) and ultra-performance liquid chromatography-mass spectrometry (UPLC-MS). Several degradation pathways of atrazine were identified in addition to those previously reported with OH center dot, H2O2, or O-3 as the main oxidizing agents. The detected degradants included des-ethyl atrazine, hydroxy atrazine and de-ethylated oligomers of atrazine with the isopropyl group being largely preserved. An atrazine degradation mechanism under DBD conditions is proposed that is consistent with the intermediates identified and supports the dominant involvement of singlet oxygen in initiating the degradation under DBD conditions.