Métodos biofotônicos no monitoramento dos mecanismos de ação do benzo[a]pireno no aparato fotossintético da macrófita aquática Lemna minor L. (Araceae)

Abstract

Polycyclic Aromatic Hydrocarbons (PAHs) are organic contaminants widely distributed in the environment, among which Benzo[a]pyrene (BaP) stands out due to its persistence and toxicological relevance. This study evaluated the effects of BaP on the photosynthetic apparatus of the aquatic macrophyte Lemna minor L. using biophotonic methods based on optical spectroscopy and chlorophyll a fluorescence. The research comprised in vitro and in vivo assays employing Synchronous Fluorescence Spectroscopy (SFS), Excitation-Emission Matrices (EEMs), Pulse-Amplitude Modulated fluorescence (PAM), fluorescence imaging, OJIP Transients, and Laser-Induced Chlorophyll Fluorescence (LICF). SFS enabled the characterization and quantification of BaP both as an isolated standard and in a PAH mixture, with Δλ = 40 nm providing the best spectral definition. In the in vitro assays, increasing BaP concentrations progressively quenched chlorophyll fluorescence, indicating an interaction between the contaminant and the fluorescent system. In the in vivo assays, BaP exposure altered the F₀, Fm, Fv/Fm, NPQ, and Rfd parameters, indicating progressive impairment of photosynthetic efficiency and vitality in L. minor. The OJIP curves revealed changes in the O-J, J-I, and I-P phases associated with QA reduction, electron transfer between QA and QB, the redox state of the plastoquinone pool, and subsequent stages of electron transport. The biophysical parameters derived from the JIP test showed increased energy dissipation and reduced photosynthetic performance over the exposure period. Laser-induced fluorescence analyses revealed changes in the emission bands near 680 and 735 nm, with more pronounced alterations in the F₆₈₀/F₇₃₅ ratio after 72–96 h, indicating late photosynthetic impairment. Overall, the results demonstrate that BaP progressively alters the dynamics of energy utilization, transport, and dissipation in the photosynthetic apparatus of L. minor, and that biophotonic methods constitute complementary, non-destructive tools for linking contaminant exposure to photophysiological responses in aquatic photosynthetic organisms.