Impact of Heavy Metal Pollution on the Biotic and Abiotic Components of the Environment

The environment comprises of biotic and abiotic components interacting as a system. The environment also contains organic and inorganic minerals in optimal concentration required by living organisms for growth, development, and metabolic activities. Due to anthropogenic activities and some natural occurrences, the availability of these elements has drastically increased in the ecosystem beyond the required threshold and permissible limits causing pollution. Heavy metal (HM) is one of the naturally occurring elements that threaten plant, animal, and human health. These HMs have been defined as elements with more than 5gcm-3 relative density that are not readily biodegradable but can be transformed from one state to another and are usually associated with toxicity or ecotoxicity. However, some heavy metals are biologically essential elements required in the body/plant or as constituents of important enzymes although in trace amounts while others are non-essential and are ranked as priority metals due to their high level of toxicity with no biological importance even at low concentrations. The non-degradability property of heavy metals contributes to its persistence and subsequent accumulation in the biota and the food chain which is of public health significance to humans and animals. The soil environment is highly prone to HM contamination due to physiological, biochemical, metabolic, and biogeochemical processes that occur within the environment mostly mediated by microbes. These microbes are inarguably the drivers of ecosystem functioning, although they are significantly the most affected by HM pollution. This review, therefore, describes the ecotoxicological effect of heavy metals with special reference to the soil environment. Other sections discussed are the toxicity and general properties of some selected heavy metal, their role as environmental pollutants and essential elements. In addition, the effect of HM on soil microbes has also been analyzed in two folds: i) reduction in microbial population and diversity and ii) increased diversity and abundance of HM-resistant microbial strains which are significant in bioremediation studies