In recent years, many new pesticides have been developed to meet the growing agricultural demands driven by global population growth. Unfortunately, this has led to their frequent detection in aquatic ecosystems, posing risks to non-target organisms and human health through environmental pollution and dietary exposure. Therefore, there is an urgent requirement to develop effective technologies to remove these pesticides from the environment. However, due to the complexity of pesticide structures, their degradation products are commonly unknown and may result in new environmental risks.
Permanganate is a strong oxidant and plays a vital role in drinking water purification, groundwater remediation, and wastewater treatment. It does not introduce new pollutants, and its reduction product, manganese dioxide, can also act as a coagulant to further remove pollutants.
In this study, we used experimental and theoretical methods to explore how potassium permanganate degrades pesticides. The reaction between permanganate and quinclorac was first studied, showing a bimolecular reaction mode, which is stable in a wide pH range. The UPLC-Q-TOF-MS analysis showed that the initial product was mono-hydroxylated quinclorac, which was formed by permanganate oxidation at the benzene ring and could be further oxidized to a less toxic catechol structure.
It is then hypothesized that permanganate oxidation is selective for certain functional groups, better than non-selective oxidants like hydroxyl radical. Then, the imidacloprid degradation by permanganate was further studied. The reaction was stable and efficient near neutral pH and different ion strengths. Background substances like humic acid and chloride ions in water barely affected degradation. UPLC-Q-TOF-MS analysis showed that the main pathway was C-H bond hydroxylation on the imidazole ring, finally leading to the breakage of the imidazole ring. Toxicity analysis with the ECOSAR program showed that the degradation products of imidacloprid by permanganate oxidation were less toxic to aquatic organisms.
