Biosorption of Toxic Metals/Metalloids by Fungi: A Solution to Contaminated Soil

Abstract

Toxic metals and metalloids, such as lead, mercury, cadmium, and arsenic, are commonly found in industrial wastewater, soil, and groundwater due to anthropogenic activities, including mining, smelting, and the manufacturing of chemicals, electronics, and batteries. The discharge of these toxic substances into the environment can have severe consequences on the ecosystem and human health, such as cancer, neurological disorders, and developmental impairments. The high toxicity and persistence of these substances make it challenging to remove them from contaminated sites, and conventional technologies for treating metal-contaminated water and soil, such as chemical precipitation, ion exchange, and membrane filtration, are expensive, energy-intensive, and generate secondary wastes. To address these challenges, researchers have turned to alternative treatment technologies, such as bioremediation, which utilizes microorganisms, including bacteria, algae, and fungi, to detoxify metal-contaminated environments. Among these microorganisms, fungi have attracted attention due to their unique chemical and physical properties, including a high surface area-to-volume ratio, large surface charge, and a high content of chelating agents, such as carboxyl, amino, and hydroxyl groups, on their cell walls and exudates. These properties allow fungi to adsorb, precipitate, and transform toxic metals and metalloids through a variety of mechanisms, including ion exchange, electrostatic attraction, biosorption, and biomineralization. Fungal biomass has been shown to be effective in removing a wide range of heavy metals and metalloids, such as copper, zinc, chromium, nickel, selenium, and antimony, from aqueous solutions and contaminated soils. Several fungal species have been reported to have high metal adsorption capacities, including Aspergillus niger, Penicillium chrysogenum, Trichoderma harzianum, Mucor hiemalis, Rhizopus arrhizus, and Pleurotusostreatus. The efficiency of metal removal by fungi depends on various factors, such as the fungal species, biomass concentration, pH, temperature, metal concentration, and the presence of competing ions and organic compounds. The biosorption of toxic metals and metalloids by fungal biomass has several advantages over conventional treatment technologies, such as low cost, eco-friendliness, scalability, and the ability to handle complex metal mixtures and low metal concentrations. Moreover, fungal biomass can be easily harvested and regenerated, and the metal-loaded biomass can be utilized for the recovery of metals or transformed into value-added products, such as biochar, biofuels, and bioplastics. Therefore, the use of fungal biomass for metal bioremediation holds great promise for addressing the global problem of metal pollution and providing sustainable solutions for the circular economy.