3 - Death in the Fields: Microbial ‘Destruction’ in Polluted Soils

Summary

The introduction and persistence of industrial pollutants in soil is recognized as an increasingly urgent environmental concern. Soil pollution can occur via a number of sources like volcanic eruptions or mineral percolation, but it mainly originates from anthropogenic endeavours such as agricultural practices, waste management, and the metallurgical and smelting industry. These and other human activities generate and disperse heavy metals such as copper, lead, nickel, zinc, cadmium, platinum, chromium and arsenic. It is widely acknowledged that the presence of heavy metals in soil has a negative impact on the ecological surroundings. Industrial waste and residues can accumulate and persist in soil in the long term, with damaging effects on the ecosystem and on human health. Specifically, the environmental pollution of soil can lead to serious imbalances in the abundant microbial communities living underground (Lenart-Boroń and Boroń, 2013). Among their many activities, microbes assist plants in finding nutrients and they contribute to the formation and structure of soil. Some naturally occurring metals with metabolic or cell enhancing properties can be sustained by the ecosystem and turn useful for microbial life and development, whereas high concentrations of metals with no biological functions can become harmful, disruptive and toxic. Among the damaging effects, these chemicals can lead to a decreased abundance and destruction – death – of the soil microbiome, a term indicating the complex community of microorganisms inhabiting a specific environment or host, such as oceans, animals and plants (Microbiology Society, 2017). The health of soil microbial communities in turn has an impact on the wider soil ecosystem.

Removing heavy metals entirely from the environment is a problematic undertaking. While prevention is recognized as most effective in avoiding heavy metal pollution, in many sites this is no longer feasible. Solutions adopted so far include the relocation of the contaminated soil to landfill or incineration of the pollutants, but these have proved to be expensive and potentially hazardous practices (Vidali, 2001). What is emerging as scientifically interesting however is the high tolerance to heavy metals shown by strains of microbes like Firmicutes, bacteria capable of enduring heavy metals such as lead and zinc (Fajardo et al, 2019).