Photo-degradation behavior of seven benzoylurea pesticides with C3N4 nanofilm and its aquatic impacts on Scendesmus obliquus

Present concerns on the residual benzoylurea pesticides (BUPs) are rapidly climbing as their market shares increase and now seven typical compounds were picked to study their photo-degradation behavior and ecological impacts. Carbon nitride (C3N4) nanofilm at a thickness of 50-80 nm was built on the glass slides and utilized to evaluate the photostability of pesticides under visible light. The results showed that the nano-C3N4 can promote the degradation efficiency of BUPs and it follows the first-order dynamic mechanism. They could be divided into three categories with the substituents and their degradations were discriminated in order of chlorofluoro-, chlorofluoroalkoxy- and chlorofluorophenoxy- substituted ones. Analyzing the intermediates by UHPLC-MS, it can be speculated that the similar pathways came to BUPs such as cleavage of urea-bridge, hydroxylation and dehalogenation. It is attractive that they all passed into a same molecule, 2-fluorobenzamide (m/z, 301.14). Moreover Scendesmus obliquus was applied to indicate the ecological impacts of originals and their photoproducts. Exposed to pesticides, the levels of chlorophyll a demonstrated much more inhibition than chlorophyll b. Lufenuron and chlorfuazuron among seven showed the higher toxicity for algal cells and finally the photodegradation products showed the lowest toxicity. The activities of antioxidant enzymes happened to a significant remedy after photodegradation. It can be concluded that the residual BUPs under visible-light irradiation may degrade through similar pathways and reduce the aquatic toxicity with the presence of C3N4 nanofilm.