Metal Oxide Engineered Nanomaterial Effects on Soil Function and Microbial Communities
Nanotechnology is a rapidly growing, innovative technology that exploits the novel properties of engineered nanomaterials (ENMs) to develop new materials and products and/or enhance the performance of existing products. ENMs entering the environment directly (e.g., nanoagrochemicals) or indirectly (released during all life cycle phases) may become the next emerging category of contaminants with little known of potential toxic effects. The nano forms of the metals molybdenum oxide (MoO3), nickel oxide (NiO) and lithium oxide (Li 2O) are finding wide application in advanced technologies including batteries and fuel cells. We evaluated soil responses to nanoMoO3, nanoNiO, and nanoLi2O as some environmental release of the materials, either directly or following the land application of biosolids, is expected. Using Drummer soil (Fine-silty, mixed, superactive, mesic Typic Endoaquolls), we evaluated the impacts of the three nanometals on soil gas emissions, enzyme activities (β-glucosidase (BG) and urease), and microbial community structure in 60 day microcosm incubation. Soil treated with nanoLi2O released 3.45 times more CO2 with respect to the control. Additionally, BG activity decreased while urease activity increased following nanoLi2O treatment. While no clear patterns were observed for gas emissions in soils exposed to nanoMoO3 and nanoNiO, a temporary suppression of BG in soil treated with either metal was detected. All three domains of microbial community were affected by increasing metal concentrations, except the archaea community under nanoLi2O presence. Further, we analyzed response to chemical pollution with nanoLi2O and nano and bulk forms of MoO3, NiO, and ZnO, during the 14 days following initial exposure. NanoLi2 O, ZnO, and MoO3, induced distinctive perturbations on soil microbial community diversity and composition. Soil exposed to nanoLi 2O showed the most drastic response, with disturbed microbial communities, increased soil pH and soil basal respiration, and decreased soil enzyme activity. ZnO also affected soil function, with an increased pH and BG enzyme activity while decreasing β-N-acetylglucosamidase and soil basal respiration. NiO increased soil pH with no effects on soil enzymes or basal respiration. Next (current) generation sequencing identified bacterial phyla across all samples with Proteobacteria, Acidobacteria, Bacteroidetes, Verrucomicrobia and Actinobacteria dominant. The relative abundance of Acidobacteria, Chloroflexi and Armatimonadetes and WS3 (candidate phylum "Latescibacteria") decreased in soils exposed to nanoLi2O, while Bacteroidetes, Nitrospirae, and Verrucomicrobia increased. Under MoO3 exposure, Acidobacteria increased while Bacteroidetes bacterial phyla decreased. In contrast, under ZnO, bacterial Phylum Bacteroidetes increased. This study provides evidence that soil microbial diversity and composition were influenced by the presence of nanoLi2O, nanoMoO3, and nanoZnO. However, through the assessment of toxicity provided here, there is no evidence that the toxicity was caused by nano-effects.^
Ronald F. Turco, Purdue University, Loring F. Nies, Purdue University.
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