Applications of Microbial Communities for the Remediation of Industrial and Mining Toxic Metal Waste: A Review

The increased amount of heavy metal pollution, due to rapid urbanization is one of the main reasons for ecosystem degradation. The sewer systems of industries, as well as the mining grounds, are the potential sources of toxic heavy metals. Broad application of mutagenic metals in different industrial processes results in their bioaccumulation in the soil ecosystem. The primary metal wastes are mercury, arsenic, lead, cadmium, cyanide, chromium, etc. Long-term exposure to even the low concentration of metals induces multiple health hazards and organ failure. The safe removal or treatment of wastes is crucial as many approaches might lead to the generation of harmful by-products or incomplete transformation of toxic metals. Therefore, eco-friendly biodegradation of toxic metals administrating efficient bioleachers is generally preferred. However, the activity of the microbes depends on their ability to tolerate large content of metals, and the use of metal-tolerant microbes found in nature is the simplest and biogenic way of degrading the metal contaminants of industries such as mining, manufacturing, textile, petroleum, plastics, etc. Microbial remediation includes the following mechanisms; surface absorption, bioleaching, transformation to less toxic products, biomineralization, and bioaccumulation. The objective of this review is to describe the industrial production and environmental occurrence of carcinogenic metals, highlight the role of the bioleachers in the decontamination process, harmful effects of toxic metals, and microbial bioleaching mechanism.