ABSTRACT
Rapid globalization and industrialization have led to the production and disposal of a large amount of heavy metals in the environment. Heavy metals such as iron, manganese, zinc, cobalt and molybdenum are required by human body in small amounts, but heavy metals such as mercury, cadmium, chromium, arsenic, nickel and lead have toxic effects on humans. Heavy metals are hazardous pollutants due to their persistent nature (long half-life), and their entrance into food chain leads to bioaccumulation. When consumed, they do not undergo metabolic degradation; therefore, their excretion from the body is difficult. Mutagenicity, carcinogenicity, immunosuppression, teratogenicity, effects on reproduction, skeletal lesions and dysfunction of organs such as kidney and liver are the main toxic effects of heavy metals on humans. The toxicity of any heavy metal depends upon the dose, exposure period, type of species, gender and nutritional and environmental factors. For the efficient removal of heavy metals from polluted sites, several conventional technologies have already been used, but they are not suitable due to their high cost and low efficiency and have numerous environmental hazards. Compared to other methods, bioremediation is an eco-friendly and cost-efficient alternative for the elimination of heavy metals from contaminated sites. This chapter gives an overview of the sources and effects of various heavy metals along with the active and emergent bioremediation techniques meant for decontamination of heavy metal-polluted ecosystems.
