From Metal-Related Public Health Risks to Bioremediation: The Potential of the Polyextremophilic Galdieria spp.—A Systematic Review

The growing demand for rare earth elements (REEs), heavy metals (HMs) and precious metals (PMs) has intensified interest in sustainable recovery strategies from secondary resources, including mining residues, industrial effluents and waste electrical and electronic equipment (WEEE). These streams represent exposure interfaces, because soluble and bioavailable metal species may persist, bioaccumulate and contribute to oxidative stress, genotoxicity, carcinogenic outcomes and chronic systemic effects. This systematic review, conducted following PRISMA guidelines, evaluates the thermoacidophilic red microalga Galdieria spp. as an extremophilic platform for metal bioremediation, recovery and upstream risk reduction. Galdieria spp. combines tolerance to low pH, elevated temperature and high metal loads with rapid surface biosorption and, in living biomass, slower intracellular sequestration and detoxification. Its interaction with REEs, PMs and toxic HMs is mediated by cell-wall functional groups, extracellular polymeric substances, redox-active processes and metabolic flexibility shaped partly by horizontal gene transfer (HGT). The review discusses matrix complexity and adsorption–desorption cycles, highlighting their implications for real industrial streams. Overall, Galdieria spp. emerges as a robust extremophilic bio-interface for selective metal recovery, hazardous waste mitigation, circular-economy biorefinery models and prevention of metal-associated risks to environmental and human health, while current scale-up limitations and process-oriented research priorities are identified.