Uptake and speciation of zinc in edible plants grown in smelter contaminated soils

PLoS One. 2020 Apr 17;15(4):e0226180. doi: 10.1371/journal.pone.0226180. eCollection 2020.

Abstract

Heavy metal accumulation in edible plants grown in contaminated soils poses a major environmental risk to humans and grazing animals. This study focused on the concentration and speciation of Zn in different edible plants grown in soils contaminated with smelter wastes (Spelter, WV, USA) containing high levels of the metals Zn, Cu, Pb, Cd. Their accumulation was examined in different parts (roots, stem, and leaves) of plants and as a function of growth stage (dry seed, sprouting seed, cotyledon, and leaves) in the root vegetables radish, the leafy vegetable spinach and the legume clover. Although the accumulation of metals varied significantly with plant species, the average metal concentrations were [Zn] > [Pb] > [Cu] > [Cd]. Metal uptake studies were complemented with bulk and micro X-ray absorption spectroscopy (XAS) at Zn K-edge and micro X-ray fluorescence (μXRF) measurements to evaluate the speciation and distribution of Zn in these plant species. Dynamic interplay between the histidine and malate complexation of Zn was observed in all plant species. XRF mapping of spinach leaves at micron spatial resolution demonstrated the accumulation of Zn in vacuoles and leaf tips. Radish root showed accumulation of Zn in root hairs, likely as ZnS nanoparticles. At locations of high Zn concentration in spinach leaves, μXANES suggests Zn complexation with histidine, as opposed to malate in the bulk leaf. These findings shed new light on the dynamic nature of Zn speciation in plants.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Environmental Monitoring
  • Plant Leaves / chemistry
  • Plant Leaves / metabolism
  • Plant Roots / chemistry
  • Plant Roots / metabolism
  • Plants, Edible / chemistry
  • Plants, Edible / metabolism*
  • Raphanus / chemistry
  • Raphanus / metabolism
  • Seeds / chemistry
  • Seeds / metabolism
  • Soil / chemistry
  • Soil Pollutants / analysis*
  • Soil Pollutants / metabolism
  • Spinacia oleracea / chemistry
  • Spinacia oleracea / metabolism
  • Trifolium / chemistry
  • Trifolium / metabolism
  • Vegetables / chemistry
  • Vegetables / metabolism*
  • Zinc / analysis*
  • Zinc / metabolism

Substances

  • Soil
  • Soil Pollutants
  • Zinc

Grants and funding

This work was funded by National Science Foundation through grant to BM and SM. X26A was supported by the Department of Energy (DOE) - Geosciences (DE-FG02-92ER14244 to The University of Chicago - CARS) and DOE - Office of Biological and Environmental Research, Environmental Remediation Sciences Div. (DE-FC09-96-SR18546 to the University of Kentucky). Use of the NSLS was supported by DOE under Contract No. DE-AC02-98CH10886.