Functionalized silver nanoparticles enable efficient mercury removal and toxicity reduction toward microalgae

Water pollution, caused by human activities, is a major environmental and health concern. Among heavy metal pollutants, mercury (Hg) is recognized as one of the most persistent and bioaccumulative, while being also highly toxic for human health. Heavy metal removal from water presents significant challenges, and nanotechnology provides a promising solution through cost-effective, efficient, and reusable adsorption or immobilization. Silver nanoparticles functionalized with citrate and L-cysteine (AgNPcitLcys) have been specifically designed to remove Hg ions from water along with a negligible ecotoxicological impact to aquatic life. The present study aims to assess the efficacy of Hg removal from water by AgNPcitLcys through and ecotoxicity approach using the freshwater microalga Raphidocelis subcapitata and the marine water microalga Dunaliella tertiolecta. AgNPcitLcys showed low ecotoxicity to both microalgae, even though at high concentrations (10 mg/L) D. tertiolecta suffered a 40% inhibition of growth. Hg removal was highly efficient in marine water medium (99.26%) compared to freshwater (63.07%), regardless of the concentration of Hg. Despite removal in both media, Hg toxicity was successfully reduced by AgNPcitLcys only for D. tertiolecta. AgNPcitLcys showed to successfully work in a complex aquatic medium such as seawater, confirming their potentiality to be applied in real scenarios of water pollution by Hg.