Human exposure to heavy metals: toxicity mechanisms and health implications

Human exposure to heavy metals is inevitable as heavy metals are continually present in air, water and food. Anthropogenic and industrial activities have rapidly increased the level of human exposure to heavy metals. Some heavy metals elicit deleterious health effects even at low levels in the body system. Every heavy metal has its own specific unique mechanistic process through which it exhibits toxicity. The major mechanisms through which most heavy metals such as Cr, As, Pb, Cu, Fe, Cd, Zn, Ni cause toxicity include the generation of reactive oxygen species (ROS), inhibition of enzyme activities and attenuation of antioxidant defense systems. Heavy metal ions are known to interfere with DNA and nuclear proteins leading to DNA structural and functional impairments as well as changes that initiate carcinogenesis, apoptosis as well as modulation of cell cycle. Heavy metal toxicity alters the activity of the central nervous system, and thereby causes mental disorder, alters blood composition, and liver, kidneys, lungs functions as well as other important body organs, resulting in the escalation of assorted human diseases. Prolonged human exposure and accumulation of heavy metals in the body aggravate the progression of physical, muscular and neurological degenerative processes that mimic certain diseases such as Alzheimer’s disease and Parkinson’s disease. Heavy metals mimic hormonal activities that alter the functions of the endocrine system. Thus, efforts must be made to mitigate the extent of human exposure and accumulation of heavy metals in the body as a result of anthropogenic and industrial activities in order to prevent incidences of deleterious health challenges.