Engineered nanoparticles in the soil and their potential implications to microbial activity

Abstract

Among the factors influencing soil quality, biological indicators are reported as critically important because soil organisms directly influence soil ecosystem processes, especially the decomposition of soil organic matter and the cycling of nutrients. Hence, any factor that affects soil microbial biomass, activity and populations would necessarily affect soil quality and sustainability. Presently, a staggering number of engineered nanoparticles (ENPs) employed for industrial and environmental applications or formed as by-products of human activity are finding their way into soils. Common ENPs include the metal ENPs (elemental Ag, Au, Fe etc.), fullerenes (grouping Buckminster fullerenes, CNTs, nanocones etc.), metal oxides (TiO2, CuO, FeO2, ZnO, Al2O3, SiO2 etc.), complex compounds (Co–Zn–Fe oxide), quantum dots often coated with a polymer e.g. cadmium–selenide (CdSe) and organic polymers (dendrimers, polystyrene, etc.). The antimicrobial activity of these ENPs has been extensively studied with human pathogenic bacteria. Similarly, studies also exist on the affect of ENPs on beneficial microbes in vitro under controlled conditions. But very little information is available on how these ENPs affect microbial communities in soil under field conditions. The few published literature does suggest that among the ENPs, fullerenes and their derivatives are less toxic, while small size metal and metal oxide ENPs are detrimental to soil microbial communities. However, under field conditions, soil organic matter and related components like humic and fulvic acids could possibly negate the toxic effects of these ENPs through various mechanisms. Also, the resistance and resilience of soil microbial communities to such perturbations cannot be discounted. The paper also stresses the need for more information on interaction of ENPs with soil microorganisms under field conditions.