Role of Microorganisms in Bioavailability of Soil Pollutants

The connection between soil pollutants and human health is justly recognized by health professionals worldwide. Of the top 10 pollutants recognized by the World Health Organization, nine are soil pollutants with well-known human health hazards. Some pollutants occur naturally in soils due to various geological and pedological processes, while others enter through various human-mediated activities. In addition to well-established pollutants, some emerging contaminants (microplastics and nanoparticles) are also on the rise. Once contaminants enter the soil environment, they undergo many transformations through chemical and biological means. While organic pollutants are prone to degrade through microbial-driven activities, inorganic contaminants tend to remain in soil for a long period of time. In addition to soil properties and climate, soil microbes play a role in shaping the mobility, bioavailability, and toxicity of contaminants, thus deciding their fate. Microbes interactively influence the bioavailability of soil pollutants through many mechanisms. In these mechanisms, microbes play a reciprocal action in determining metal speciation and mobility, influenced by site-specific conditions such as soil pH and redox potential. Various microbial activities alter soil physical and biochemical properties, thereby indirectly influencing the solubility and bioavailability of heavy metals. Thus, microorganisms make soil contaminants such as heavy metals available for uptake, facilitating their entry into terrestrial food webs. Microbes use pollutants as a source of carbon or substrate, thus degrading them into less toxic forms through extracellular enzymatic activities (EEA). EEA is also known to be a key factor in the heavy metal speciation process in soils that regulates their bioavailability. Recent advancements in research related to the soil microbiome have improved our understanding of microbes and their interactions with other biotic and abiotic components. This new wealth of information provides opportunities for scientists to modify the role of microbes in the bioavailability of pollutants, with the ultimate aim of restoring soil health and quality. The fate and behavior of emerging soil pollutants, such as microplastics, personal care products, and nanoparticles, would set new challenges to scientists. Therefore, more efforts and resources should be put forthwith in order to explore their behavior and fate in soils. Such a concerted effort would allow the scientific community to be conscious of emerging threats and to take appropriate measures to regulate them.