Conversation of pesticide residues into ammonium nitrogen (NH4+-N) through AOPs and its fertilization effect on lettuce growth

Abstract

Eliminating pesticide residues in soil through the Advanced Oxidation Processes (AOPs) has been attracted a lot of attention in recent years. However, the potential of converting them into small molecular nutrients such as ammonium nitrogen (NH4+-N) has been significantly ignored. Herein, we systematically detected the transformation of clothianidin (CTD) into NH4+-N through AOPs and the following effect on the growth of lettuce. Fe3S4-loaded biochar (BC@Fe3S4) was synthesized in one step through hydrothermal method, possessing excellent catalytic capacity to activate peroxymonosulfate (PMS). The results showed that the generated NH4+-N could reach up to 3.029 mg L−1 in soil–water system containing 20 mg L−1 of CTD after the treatment of BC@Fe3S4 + PMS. However, when the concentration of CTD in soil was 20 mg kg−1, the dry weight of lettuce was 17.3 mg/plant, and the dry weight of lettuce in CTD-contaminated soil with this concentration was 29.3 mg/plant after treatment by BC@Fe3S4 + PMS, and no CTD residue was detected. The results of lettuce cultivation showed that CTD in the system was converted to NH4+-N after treatment with BC@Fe3S4 + PMS, which resulted in increased dry matter accumulation and decreased residue of lettuce seedlings. Meanwhile, LC–MS/MS analysis revealed three main degradation routes involved in the CTD degradation process. T.E.S.T-QSAR was carried out to simulate the toxicity of all degradation intermediates to Fathead minnow and T.pyriformis, manifesting that the CTD toxicity decreased after BC@Fe3S4 + PMS treatment. Further analysis indicated that the degradation of CTD and the formation of NH4+-N occurred simultaneously, where •OH, 1O2 and SO4•− played a leading role in trigging those reactions. This work explains in detail the mechanism by which pesticides are converted into nutrients, providing feasible strategies and new perspectives for soil remediation.