Photolysis of nitrate by solar light in agricultural runoffs: Degradation of emerging contaminant vs. formation of unintended products

Abstract

The wide application of nitrogenous fertilizers and herbicides in agricultural activities leads to the common co-existence of nitrate (NO3−) and diuron in agricultural runoffs, which are exposed to solar light irradiation. Previous studies reported that generation of reactive species and degradation of emerging contaminants can be induced by the photolysis of NO3−. In our present study, efficient degradation of diuron in solar light/NO3− system was verified, which was enhanced by the increase of NO3− concentration (0–10 mM). Typical spectra of HO and NO were detected using electron paramagnetic resonance, directly confirming the formation of HO and reactive nitrogen species. To investigate the transformation of nitrogen in NO3−, generation of nitrite and N-dimethylnitrosamine (NDMA) in solar light/NO3− system was determined, which are typically unintended products. Further, impacts of solution pH, alkalinity, and natural organic matter on the degradation of diuron, formation of nitrite and NDMA were evaluated. Of note, some nitrated products with higher toxicruity than parent diuron were detected, which are also unintended products. The acute toxicity appeared an increasing trend during diuron degradation in the solar light/NO3− system.