Adverse effect of heavy metals (As, Pb, Hg, and Cr) on health and their bioremediation strategies: a review

Currently, heavy metal pollution becomes a severe problem whole over the world, and these toxic metals enter into the environment either by natural phenomena or due to extensive industrialization. The discharged effluents containing toxic heavy metals mixed with soil/water and change their natural composition. These heavy metals have adverse effects on living beings and cause damage to the vital body organs of animals as well as humans. The heavy metal pollution also inhibits the biodegradation of the chlorinated organic compounds (another type of environmental pollution) by interacting with metabolizing enzymes and inhibits their functioning. Earlier studies described that heavy metals cannot be fully removed from the environment, but they can be effectively neutralized or transformed into less toxic form so that their harmful effect on the environment can be reduced. The distinctive enzymatic apparatus within microbial system plays a major role in the transformation of heavy metals in the environment. A considerable advancement has been made during recent years to transform the heavy metals by utilizing the bioremediation potential of genetically engineered (GE) microorganisms. These transgenics are very much efficient in heavy metal transformations and still, we have to discover more to additionally utilize their full biotransformation potential. In the present review article, the detailed description of the adverse effects of four heavy metals (arsenic, lead, mercury, and chromium) and their adverse effect on our environment and human beings is discussed. Furthermore, the use of microorganisms/GE organisms for the bioremediation of heavy metals from the environment is also discussed along with their detailed bioremediation mechanism.