Abstract
A simple and effective tandem process of photo-electrocatalytic oxidation (PECO)-MoS2 adsorption was developed for the synchronous removal of triazole fungicides (TFs) and toxicological transformation products (TPs). In order to accurately identify trace TPs and evaluate degradation pathway during water treatment, a sensitive analytical method was developed on the basis of the stir bar sorptive extraction (SBSE) pretreatment tandem LC-MS/MS technique. Firstly, the typical TFs (PRO, TET, and DIN, C0 = 1.0 mg/L) in actual water samples were treated under the optimal process (bias voltage 1.8 V, pH 4, irradiation intensity 50 mW/cm2, 0.05 g MoS2/100 mL, 350 rpm, adsorption of 5 min). The result indicated that the residues of PRO, TET, and DIN in secondary effluent were 0.0973, 0.0617, and 0.0012 mg/L, respectively, with the removal rates of 90.3%, 93.8%, and 99.9%, respectively, undergoing 30-min photo-electrocatalysis and 5-min adsorption. The alkaline medium was favorable for the adsorption of MoS2 to TFs. The assessment results of potential cancer risk indicated that the residues of TFs in secondary effluent were safe for drinking water consumption. Besides, the major TPs were identified via the SBSE-HRLC-MS/MS technique, and one possible transformation pathway of TFs was proposed. TFs mainly underwent dehydrochlorination, cyclization, hydroxylation, etc. to produce a series of nitrogenous heterocyclic compounds that possess higher polarity than parents, hinting that TPs might pose potential aquatic toxicity. However, TPs can be removed synchronously by this tandem technique. The current study can provide a theoretical basis for the harmless treatment of TFs in the water environment.
Highlights
In order to increase the yield and harvest of agricultural products, triazole fungicides (TFs) have been widely used in agricultural production due to the characteristics of low toxicity, high efficiency, and broad spectrum
Pesticides are a kind of typical environmental exogenous substances; once they enter into the environment, they will be degraded or metabolized to a series of unknown transformation products (TPs) under the biologic and abiotic actions
It is reported that TFs are usually transformed into a series of nitrogenous heterocyclic compounds (NHCs) with unknown chemical properties in the existence of light exposure (Rodríguez-Cabo et al 2018)
Summary
In order to increase the yield and harvest of agricultural products, triazole fungicides (TFs) have been widely used in agricultural production due to the characteristics of low toxicity, high efficiency, and broad spectrum. The residues of TFs in the water environment are at the trace level (ng/L or μg/L), some TFs such as propiconazole, tebuconazole, and prothioconazole still cause teratogenesis, carcinogenesis, and mutation (Tian et al 2019; Teng et al 2019). It is reported that TFs are usually transformed into a series of nitrogenous heterocyclic compounds (NHCs) with unknown chemical properties in the existence of light exposure (Rodríguez-Cabo et al 2018). These existing technologies mainly focus on the degradation of pesticide parent, but little attention is paid to their toxicological TPs (Ying and Luo 2017; Cui et al 2017), which will inevitably lead to secondary pollution. How to achieve synchronous removal and detoxification of TFs and trace toxicological TPs in the water environment becomes an important problem to be solved urgently at present
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