The Kinetics and Mechanisms for Photodegradation of Nitrated Polycyclic Aromatic Hydrocarbons on Lettuce Leaf Surfaces: an In Vivo Study

Insights into the environmental fates of nitrated polycyclic aromatic hydrocarbons (NPAHs) in edible vegetables are of great significance for better evaluating human exposure to NPAHs through dietary pathway. In this work, a fluorescence quenching method using graphene quantum dots as a fluorescent probe was firstly applied for the in vivo determination of 9-nitroanthracene (9-NAnt) and 1-nitropyrene (1-NPyr) adsorbed on the leaf surfaces of living lettuce (Lactuca sativa L.) seedlings. Moreover, the photolysis kinetics and mechanisms of the two adsorbed NPAHs were discussed. The photodegradation kinetics followed the pseudo-first-order equation, and the photodegradation half-lives of 1-NPyr (7.4 ± 0.2 h) was greater than that of 9-NAnt (2.3 ± 0.1 h). Anthraquinone and pyrenediones were identified to be the main photolytic products of 9-NAnt and 1-NPyr, respectively. Intra-molecular rearrangement was the most reasonable mechanism for the NPAH photolysis. The photolysis-driven degradation exhibited a key r...