Toxicity of ZnO and Fe2O3 nano-agro-chemicals to soil microbial activities, nitrogen utilization, and associated human health risks

Abstract

Background Various nano-enabled agrochemicals are being extensively used for soil remediation and to boost crop production by increasing the nutrient efficiency of fertilizers. However, understanding of their potential risks on the manure–soil–plant continuum is limited. These nano-agrochemicals can be potentially toxic to soil microbes and their associated functions, such as nitrogen (N) mineralization and decomposition of organic materials. Moreover, the accumulation of nanoparticles (NPs) in edible crops may reduce food quality, and can cause serious threats to human health. Accordingly, here we investigated how zinc (ZONPs) and iron oxide (IONPs) nanoparticles affect the soil microbial communities, their efficiency of decomposition and N mineralization, radish yield, and plant N recovery after soil application of poultry manure (PM). Furthermore, we studied the associated health risks (DIM, HRI) via dietary intake of radish. Results Soil application of ZONPs and IONPs significantly (P < 0.05) increased microbial biomass Zn/Fe indicating their microbial utilization. This decreased the colony-forming units (CFU) of bacteria and fungi. For example, the application of PM with ZONPs and IONPs decreased the CFU of bacteria by 32% and 19%, respectively. In case of fungi, the CFU reductions were slightly different (ZONPs: 28% and IONPs: 23%). Consequently, the N mineralization significantly decreased by 62% and 29% due to ZONPs and IONPs, respectively. Which ultimately resulted in the reduction of radish dry matter yield by 22% and 12%. The respective reductions of the apparent N recovery (ANR) were 65% and 39%. Health risk assessment indicated that DIM and HRI values from both the NPs lie under safe limits. Conclusions We conclude that both metal oxide nanoparticles (i.e., ZONPs and IONPs) can significantly affect the soil microbial community, their associated functions, and crop yield with the former being relatively more toxic. However, no evidence was found regarding the health risks to humans via dietary radish intake. These toxicological effects imply restricting the widespread production and use of NPs, and developing strategies for their safe disposal to avoid their contact with soil beneficial microorganisms.

The unseen world beneath our feet: Heliyon soil science. Exploring the cutting-edge techniques and ambitious goals of modern soil science

“…Pollution of soils with inorganic and organic contaminants is of ever-growing concern. In addition to old burdens, mainly heavy metals and metalloids from mining activities and metal processing industries and classical organic pollutants like PCBs and PAHs, new, still poorly explored danger is coming, among others, from e-waste, pharmaceuticals, nanoparticles, microplastics and microfibers ([ 56 ] [ 57 ] [ [58] , [59] , [60] ]). How soil multifunctionality is affected by these new threats is a further hot topic that deserved research efforts, especially considering real field situations.…”

Nano-Management Approaches for Salt Tolerance in Plants under Field and In Vitro Conditions

“…The mechanism of this action may be microbial cell membrane absorption, leading to direct association with amino, carboxyl, and thiol functional groups of proteins and nucleic acids. Regarding the indirect impacts of nanotoxicity, they can be attributed to the interaction with organic toxicants after they reach cumulative effects [164]. The possible mechanisms for direct nano- Concerning the nanotoxicity on soil microbiomes, NMs have direct impacts due to their high applied dose, which reduces nutrient bioavailability.…”

“…The mechanism of this action may be microbial cell membrane absorption, leading to direct association with amino, carboxyl, and thiol functional groups of proteins and nucleic acids. Regarding the indirect impacts of nanotoxicity, they can be attributed to the interaction with organic toxicants after they reach cumulative effects [164]. The possible mechanisms for direct nanotoxicity may include the disruption of membranes, genotoxicity, forming ROS, and release of toxic constituents, as well as structural changes in the microbial membrane, disruption of the functionality of cells, and eventually the death of cells [164].…”

“…Regarding the indirect impacts of nanotoxicity, they can be attributed to the interaction with organic toxicants after they reach cumulative effects [164]. The possible mechanisms for direct nanotoxicity may include the disruption of membranes, genotoxicity, forming ROS, and release of toxic constituents, as well as structural changes in the microbial membrane, disruption of the functionality of cells, and eventually the death of cells [164]. Phytotoxicity is also an expected problem after applying intensive amounts of manufactured NMs [1].…”