Degradation of Thiamethoxam in aqueous solution by ozonation: Influencing factors, intermediates, degradation mechanism and toxicity assessment

• Main influencing factors on the degradation of Thiamethoxam in aqueous solution by ozonation were studied.
• Four intermediates were identified and the degradation mechanism was proposed.
• Toxicity changes during the ozonation process were measured.

This paper focuses on the degradation of Thiamethoxam (THIA) in aqueous solution by ozonation. Four influencing factors: pH, THIA initial concentration, ozone concentration and temperature were investigated in order to optimize the conditions, and pH showed the greatest impact; the removal efficiency reached up to 71.19% under the condition of pH 5–11, THIA initial concentration 50–300 mg L−1, the ozone concentration 10–22.5 mg L−1 at 293–308 K after 90 min. Four main intermediates were separated and identified and the possible degradation mechanism was proposed. The luminous intensity of photobacteria and the chemical oxygen demand (COD) were measured to assess the changes of toxicity and mineralization in ozonation process, and results showed that the inhibition rate decreased by 60% and 76% of COD was removed after 180 min with the THIA initial concentration was 200 mg L−1. Our study powerfully demonstrates that the degradation of THIA in aqueous solution by ozonation is a promising technology.

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