Microalgae as potential bioindicators for heavy metal pollution

Heavy metals (HMs) are considered persistent pollutants due to their low degradation rate. They can be easily accumulated along the food chain and reach the higher trophic levels, posing a threat for both the environment and human health. Microalgae, being at the base of food webs in marine and fresh waters, are one of the first groups to be affected by HM pollution and can be considered potential HM indicators in aquatic environments. In this frame we propose QPM (quantitative phase microscopy) optical techniques as an innovative approach for rapid detection of HMs stress on microalgae. Furthermore, since some HMs are considered essential elements for cell growth and metabolism, microalgae have designed strategies for their uptake and have been thus considered attractive candidates for bioremediation purposes. In the present work, a strain of Skeletonema pseudocostatum isolated from the mouth of the Sarno river (Gulf of Naples) was exposed to several concentrations of copper to test its tolerance to the HM in 72 hours small-scale experiments. A lethal (25 μM) and a sub-lethal (10 μM) copper concentration were identified and used for 72 hours scale-up experiments. The rate of copper adsorption/compartmentalization was evaluated by ICP-MS analyses of microalgal pellets at the end of each experiment. S. pseudocostatum showed tolerance to copper up to a concentration of 10 μM, with a rate of removal of 14% of copper administered in solution in larger scale experiments. These results seem promising considering future possible applications of this species for HM removal. In addition, preliminary QPM investigations of copper effects on cellular and subcellular morphology seem to suggest that these techniques could aid in elucidating S. pseudocostatum potential as a sensor of HM environmental pollution.