Identification of the gallic acid mechanism of action on mercury chloride toxicity reduction using infrared spectroscopy and antioxidant assays

Human activities have enhanced environmental contamination by heavy metals such as mercury. One of the possible approaches to reducing mercury toxicity is chelation, with several plant compounds demonstrating this effect, such as gallic acid. The objective of this study was to evaluate the antioxidant, metal chelating and cytoprotective activity of gallic acid against the action of Mercury Chloride (HgCl2). Iron II and III chelation as well as antioxidant activity assays were performed using the DPPH (1,1-Diphenyl-1-picrylhydrazyl) method. The interaction between the metal and the phenolic compound was identified by infrared spectroscopy. The Minimum Inhibitory Concentration (MIC) was determined by microdilution. From these results, and using a sub-inhibitory concentration (64 μg mL−1 for bacterial and fungal assay respectively) of the phenolic compound, the Minimum Bactericidal (MBC) and Minimum Fungicide Concentration (MFC) were evaluated. Allelopathy and cytoprotection assays were performed using eukaryotic and prokaryotic models, with a protection of the fungi being observed. When using a plant model with a sub-allelopathic concentration (32 μg mL−1), the results demonstrated the cytoprotective effect of gallic acid against HgCl2, increasing the extension of caulicles and radicles as well as their dry mass. This protection may be associated with the chelating effect of gallic acid. These results demonstrate that natural products such as gallic acid may be used for toxic metal chelation allowing plant development in polluted environments thus retrieving land usage for crops or forestry initiatives.