Marine algal polysaccharides as heavy metals biosorbents for a bioremediation strategy

Heavy metals pollution is one of major concerns for environmental and human health. Invasive macroalgae, such as those from the brackish Lake of Ganzirri (Italy) produce large amounts of biomass with attractive interests for the valuable transformation of waste into an economic and eco-friendly resource. In this contest, we evaluated the biosorbent ability of macroalgal polysaccharides to remove heavy metals from aquatic environments. In this study, crude polysaccharides (100 μg/ml) extracted from the Rhodophyta Agardhiella subulata (κ-carrageenan, A1), the Pheophyta Sargassum muticum (alginate, S1) and the Chlorophyta Ulva ohnoi (ulvan, U1) were evaluated for their capacity to absorb arsenite (AsIII), mercury (HgII) and vanadium (VV) (100 ppm), by Graphite Furnace Atomic Absorption Spectrometry (GF-AAS). Moreover, Fourier Transform Infrared Spectroscopy (FTIR) was performed to identify the functional groups of crude extracted polysaccharides (100 μg/ml) interacting with heavy metals (100 ppm). The algal extracts adsorbed AsIII, HgII and VV with different capabilities. In details, A1 showed the highest absorption level of VV (52.5%), followed by S1 (33.1%) and U1 (18.5%). HgII was greatly absorbed by S1 (30.4%) and U1 (30.3%), followed by A1 (18.3%). The arsenic absorption was negligible (≤2%) by all polysaccharides. Moreover, FTIR analysis suggested that polysaccharides from invasive marine algae possessed functional groups (especially –OH groups) capable of binding heavy metals through ion exchange mechanisms. The algal polysaccharides A1 and S1 for their ability to absorb both HgII and VV could be used to develop alternative bioremediation strategies to physical or chemical ones for the removal of heavy metals from aquatic environments.