title: Comparative phytotoxicity of ZnO NPs, bulk ZnO, and ionic zinc onto the alfalfa plants symbiotically associated with Sinorhizobium meliloti in soil.
abstract: ZnO nanoparticles (NPs) are reported as potentially phytotoxic in hydroponic and soil media. However, studies on ZnO NPs toxicity in a plant inoculated with bacterium in soil are limited. In this study, ZnO NPs, bulk ZnO, and ZnCl₂ were exposed to the symbiotic alfalfa (Medicago sativa L.)-Sinorhizobium meliloti association at concentrations ranging from 0 to 750 mg/kg soil. Plant growth, Zn bioaccumulation, dry biomass, leaf area, total protein, and catalase (CAT) activity were measured in 30 day-old plants. Results showed 50% germination reduction by bulk ZnO at 500 and 750 mg/kg and all ZnCl₂ concentrations. ZnO NPs and ionic Zn reduced root and shoot biomass by 80% and 25%, respectively. Conversely, bulk ZnO at 750 mg/kg increased shoot and root biomass by 225% and 10%, respectively, compared to control. At 500 and 750 mg/kg, ZnCl₂ reduced CAT activity in stems and leaves. Total leaf protein significantly decreased as external ZnCl₂ concentration increased. STEM-EDX imaging revealed the presence of ZnO particles in the root, stem, leaf, and nodule tissues. ZnO NPs showed less toxicity compared to ZnCl₂ and bulk ZnO found to be growth enhancing on measured traits. These findings are significant to reveal the toxicity effects of different Zn species (NPs, bulk, and ionic Zn) into environmentally important plant-bacterial system in soil.
authors.affiliation: Environmental Science and Engineering PhD program, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States; University of California Center for Environmental Implications of Nanotechnology (UC CEIN), The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States.
authors.forename: Susmita
authors.initials: S
authors.lastname: Bandyopadhyay
authors.affiliation: Department of Physics and Astronomy, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, United States.
authors.forename: Germán
authors.initials: G
authors.lastname: Plascencia-Villa
authors.affiliation: Environmental Science and Engineering PhD program, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States; University of California Center for Environmental Implications of Nanotechnology (UC CEIN), The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States.
authors.forename: Arnab
authors.initials: A
authors.lastname: Mukherjee
authors.affiliation: Department of Chemistry, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States; University of California Center for Environmental Implications of Nanotechnology (UC CEIN), The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States.
authors.forename: Cyren M
authors.initials: CM
authors.lastname: Rico
authors.affiliation: Department of Physics and Astronomy, The University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, United States.
authors.forename: Miguel
authors.initials: M
authors.lastname: José-Yacamán
authors.affiliation: Environmental Science and Engineering PhD program, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States; Department of Chemistry, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States; University of California Center for Environmental Implications of Nanotechnology (UC CEIN), The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States.
authors.forename: Jose R
authors.initials: JR
authors.lastname: Peralta-Videa
authors.affiliation: Environmental Science and Engineering PhD program, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States; Department of Chemistry, The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States; University of California Center for Environmental Implications of Nanotechnology (UC CEIN), The University of Texas at El Paso, 500 West University Ave., El Paso, TX 79968, United States. Electronic address: jgardea@utep.edu.
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Gardea-Torresdey
mesh_terms: D018527:Hydroponics; D000455:Medicago sativa / Q000187:drug effects* / Q000382:microbiology / Q000502:physiology; D053758:Nanoparticles / Q000633:toxicity*; D016962:Sinorhizobium meliloti / Q000187:drug effects* / Q000502:physiology; D012987:Soil; D012988:Soil Microbiology; D012989:Soil Pollutants / Q000633:toxicity*; D013559:Symbiosis; D015034:Zinc Oxide / Q000633:toxicity*
chemical_list: D012987:Soil; D012989:Soil Pollutants; D015034:Zinc Oxide
keywords: Bulk ZnO; General plant behavior; Ionic Zn; Toxicity; Zn uptake; ZnO nanoparticles