BIOADSORPTION OF HEAVY METALS BY POLYSACCHARIDES EXTRACTED FROM INVASIVE MARINE MACROALGAE

Macroalgae inhabiting transitional environments, such as the brackish lake of Ganzirri (Messina, Italy), produce large amounts of biomass which needs to be periodically removed and treated as waste. Macroalgal polysaccharides possess several activities with attractive interest for the valuable transformation of waste into an economic and eco-friendly resource. Due to the anthropic activities, the concentration of heavy metals in the aquatic ecosystems is increasing, with negative consequences on the environmental and human health. In this study, crude polysaccharides extracted from Agardhiella subulata (Rhodophyta), Ulva ohonoi (Chlorophyta) and Sargassum muticum (Pheophyta) were evaluated for their biosorption of mercury, arsenic and vanadium (100ppm) by the ATR-FTIR spectroscopy. Carragenans from A. subulata (A1), alginate from S. muticum (S1) and ulvans from U. ohnoi (U1) were the main polysaccharides chemically identified. The spectra from the three polysaccharides after the exposition to As (III) and Hg (II) showed significant modifications in the peaks observed in the region attributed to OH groups of carbohydrates (800 to 1250 cm-1 ), whereas no changes were observed after exposition to V (V). In details, changes in the spectra of A1 and U1 indicated that both carragenans and ulvans adsorbed Hg, mainly through the adsorbed complexation of Hg ions by the polysaccharidic OH groups. Moreover, spectra showed that carragenans adsorbed As, by both OH groups and carbons bonds (C-C) (2930 and 815 cm-1 ). Exposed to As and Hg, S1 spectra showed significant changes in the region attributed to C-C bonds, but did not in that of OH groups, suggesting a weak interaction between alginate and these heavy metals. The collection of invasive, marine algal species may represent a double chance both for the mitigation of their negative impacts, and transforming waste into valuable resource of polysaccharides that could be used to remove heavy metals from aquatic systems.