Sodium persulfate activated by solar radiation to generate sulfate anion radicals for degradation of the insecticide thiamethoxam in water

The degradation of the neonicotinoid insecticide Thiamethoxam (TMX) by the oxidizing agent sodium persulfate (SP) activated by H2O2, peracetic acid (PAA), pH, solar radiation, heating and sonication, also using combinations between the activators was evaluated. The optimal dosage of SP in the process was 10 mmol L−1 and at this concentration the oxidants hydrogen peroxide and PAA did not contribute to the increase in TMX degradation even when exposed to solar radiation. Under conditions of greater acidity and exposure to solar radiation, the degradation efficiency of TMX increased and continued for days, even with sample storage in the absence of light. The process promoted a drastic reduction in the pH of the medium, meaning that it always occurred at an acidic pH, regardless of the initial pH. The degradation kinetics of TMX can be described by a Pseudo-second order model with higher reaction rate in acidic medium. Analysis employing a sequestering agent (isopropyl alcohol) indicated that the degradation efficiency of the process can be attributed to the generation of HO• and SO4−• radicals. Ecotoxicological analyses show greater toxicity of the sample after TMX degradation.