Perfluorooctanoic acid and perfluorooctane sulfonate co-exposure induced changes of metabolites and defense pathways in lettuce leaves.

Growing evidence shows plants are at risks of exposure to various per- and polyfluoroalkyl substances (PFASs), however the phytotoxicity induced by these compounds remains largely unknown on the molecular scale. Here, lettuce exposed to both perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) at different concentrations (500, 1000, 2000 and 5000 ng/L) in hydroponic media was investigated via metabolomics. Under the co-exposure conditions, the growth and biomass were not affected by PFOA and PFOS, but metabolic profiles of mineral elements and organic compounds in lettuce leaves were significantly altered. The contents of Na, Mg, Cu, Fe, Ca and Mo were decreased 1.8%-47.8%, but Zn was increased 7.4%-24.2%. The metabolisms of amino acids and peptides, fatty acids and lipids were down-regulated in a dose-dependent manner, while purine and purine nucleosides were up-regulated, exhibiting the stress response to PFOA and PFOS co-exposure. The reduced amounts of phytol (14.8%-77.0%) and abscisic acid (60.7%-73.8%) indicated the alterations in photosynthesis and signal transduction. The metabolism of (poly)phenol, involved in shikimate-phenylpropanoid pathway and flavonoid branch pathway, was strengthened, to cope with the stress of PFASs. As the final metabolites of (poly)phenol biosynthesis, the abundance of various antioxidants was changed. This study offers comprehensive insight of plant response to PFAS co-exposure and enhances the understanding in detoxifying mechanisms.