Metal Pollution in Water: Toxicity, Tolerance and Use of Algae as a Potential Remediation Solution

Metals are persistent pollutants which, in consequence of their accumulation in water bodies, can exert dangerous effects on human health and on the ecosystem. Conventional techniques used for their removal are expensive, energy-consuming and can release additional noxious chemicals, all aspects that could be overcome through the use of living organisms for bioremediation purposes. Algae are naturally exposed to complex and stressful environments so that they possess a certain degree of resistance to metal toxicity, thanks to physiological defence mechanisms that are at the basis of the utility for bioremediation. Both living and dead micro- and macroalgae were successfully demonstrated to sequester different metals from aqueous solutions, the main advantages being the high selectivity and affinity also at low metal concentrations and the possibility to interact with multiple ions. On the other hand, the process is species-specific, as algae are very diverse in composition, growth requirements, resistance to pre- and post-treatments and their use usually requires tailored processes. This chapter summarizes the basic aspects of cells interactions with the metals and the evidences of the great utility these organisms can have in metal removal. It analyses the applicative achievements obtained until now which are still at a base level due to the complex nature of real wastewaters and to the difficulty in scaling up the process at industrial level.