Effect of ZnO nanoparticles on Zn, Cu, and Pb dissolution in a green bioretention system for urban stormwater remediation
Chemosphere, 2021, 282, pages 131045. https://doi.org/10.1016/j.chemosphere.2021.131045
Stable Zn isotopes reveal the uptake and toxicity of zinc oxide engineered nanomaterials in Phragmites australis
Environmental Science: Nano, 2020, 7, pages 1927-1941. DOI: 10.1039/D0EN00110D
The uptake, transport, and toxicity mechanisms of zinc oxide (ZnO) engineered nanomaterials (ZnO-ENMs) in aquatic plants remain obscure. We investigated ZnO-ENM uptake and phytotoxicity in Phragmites australis by combining Zn stable isotopes and microanalysis. Plants were exposed to four ZnO materials: micron-size ZnO, nanoparticles (NPs) of <100 nm or <50 nm, and nanowires of 50 nm diameter at concentrations of 0–1000 mg l−1. All ZnO materials reduced growth, chlorophyll content, photosynthetic efficiency, and transpiration and led to Zn precipitation outside the plasma membranes of root cells. Nanoparticles <50 nm released more Zn2+ and were more toxic, thus causing greater Zn precipitation and accumulation in the roots and reducing Zn isotopic fractionation during Zn uptake. However, fractionation by the shoots was similar for all treatments and was consistent with Zn2+ being the main form transported to the shoots. Stable Zn isotopes are useful to trace ZnO-ENM uptake and toxicity in plants.
Our understanding of zinc oxide nanomaterials interaction with wetland plants is hampered by the lack of scientific consensus about their uptake and toxicity mechanisms in these species. This is a serious concern given the alarming global increase in the discharge of these nanomaterials into the environment and the key ecological roles of wetland plants. The Zn isotopic signature of plant tissue integrates all the Zn metabolic pathway throughout the plant’s life, giving insight about the form of Zn taken up, even if this later transforms into another Zn species. Thus, our findings clarify the exposure routes and the mechanisms of action of zinc oxide engineered nanomaterials in wetland plants while advancing the toolbox for plant physiology and environmental studies.
Assessment of Metal Immission in Urban Environments Using Elemental Concentrations and Zinc Isotope Signatures in Leaves of Nerium oleander
A thorough understanding of spatial and temporal emission and immission patterns of air pollutants in urban areas is challenged by the low number of air-quality monitoring stations available. Plants are promising low-cost biomonitoring tools. However, source identification of the trace metals incorporated in plant tissues (i.e., natural vs anthropogenic) and the identification of the best plant to use remain fundamental challenges. To this end, Nerium oleander L. collected in the city of Zaragoza (NE Spain) has been investigated as a biomonitoring tool for assessing the spatial immission patterns of airborne metals (Pb, Cu, Cr, Ni, Ce, and Zn). N. oleander leaves were sampled at 118 locations across the city, including the city center, industrial hotspots, ring-roads, and outskirts. Metal concentrations were generally higher within a 4 km radius around the city center. Calculated enrichment factors relative to upper continental crust suggest an anthropogenic origin for Cr, Cu, Ni, Pb, and Zn. Zinc isotopes showed significant variability that likely reflects different pollution sources. Plants closer to industrial hotspots showed heavier isotopic compositions (δ66ZnLyon up to +0.70‰), indicating significant contributions of fly ash particles, while those far away were isotopically light (up to −0.95‰), indicating significant contributions from exhaust emissions and flue gas. We suggest that this information is applied for improving the environmental and human risk assessment related to the exposure to air pollution in urban areas.
Zinc isotopic fractionation in Phragmites australis in response to toxic levels of zinc.
Stable isotope signatures of Zn have shown great promise in elucidating changes in uptake and translocation mechanisms of this metal in plants during environmental changes. Here this potential was tested by investigating the effect of high Zn concentrations on the isotopic fractionation patterns of Phragmites australis (Cav.) Trin. ex Steud. Plants were grown for 40 d in a nutritive solution containing 3.2 μM (sufficient) or 2 mM (toxic) Zn. The Zn isotopic composition of roots, rhizomes, shoots, and leaves was analysed. Stems and leaves were sampled at different heights to evaluate the effect of long-distance transport on Zn fractionation. During Zn sufficiency, roots, rhizomes, and shoots were isotopically heavy (δ66ZnJMC Lyon=0.2‰) while the youngest leaves were isotopically light (–0.5‰). During Zn excess, roots were still isotopically heavier (δ66Zn=0.5‰) and the rest of the plant was isotopically light (up to –0.5‰). The enrichment of heavy isotopes at the roots was attributed to Zn uptake mediated by transporter proteins under Zn-sufficient conditions and to chelation and compartmentation in Zn excess. The isotopically lighter Zn in shoots and leaves is consistent with long-distance root to shoot transport. The tolerance response of P. australis increased the range of Zn fractionation within the plant and with respect to the environment.