In Situ Metal Imaging and Zn Ligand-Speciation in a Soil-Dwelling Sentinel: Complementary Electron Microprobe and Synchrotron Microbeam X‑ray Analyses

• Published in: Environmental science & technology 2013-01, Vol.47 (2), p.1073-1081
• Main Authors: Morgan, A. J, Mosselmans, J. F. W, Charnock, J. M, Bennett, A, Winters, C, O’Reilly, M, Fisher, P, Andre, J, Turner, M, Gunning, P, Kille, P
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Biological and medical sciences; Cadmium - analysis; Cadmium - metabolism; Cellular biology; Ecotoxicology, biological effects of pollution; Effects of pollution and side effects of pesticides on protozoa and invertebrates; Electron Probe Microanalysis; Environmental Monitoring; Fundamental and applied biological sciences. Psychology; Lead - analysis; Lead - metabolism; Lead content; Ligands; Oligochaeta - metabolism; Oligochaeta - ultrastructure; Soil - analysis; Soil Pollutants - analysis; Soil Pollutants - metabolism; Spectrum analysis; Synchrotrons; Terrestrial environment, soil, air; Transmission electron microscopy; Worms; X-Ray Absorption Spectroscopy; X-Rays; Zinc; Zinc - analysis; Zinc - metabolism
• ISSN: 0013-936X; 1520-5851
• DOI: 10.1021/es302633f

Understanding the relationships between accumulated metal speciation in cells and tissues of ecologically significant taxa such as earthworms will improve risk assessments. Synchrotron-based μ-focus X-ray spectroscopy was used to detect, localize, and determine ligand-speciation of Zn and Pb in thin sections of two epigeic earthworm species collected from a Pb/Zn-mine soil. The findings indicated that Zn and Pb partition predominantly as typical hard acids (i.e., strong affinities for O-donors) within liverlike chloragocytes. Moreover, Zn speciation was very similar in the chloragog and intestinal epithelia but differed subtly in the kidneylike nephridial tubules; neither Zn nor Pb was detectable in the ventral nerve cord. High resolution X-ray mapping of high pressure-frozen, ultrathin, freeze-substituted sections in a transmission electron microscope (TEM), combined with conventional TEM structural analysis, identified a new cell type packed with highly organized rough endoplasmic reticulum and containing deposits of Cd (codistributed with S); there was no evidence that these cells are major depositories of Zn or Pb. These data may be used in a systems biology approach to assist in the interpretation of metal-evoked perturbations in whole-worm transcriptome and metabolome profiles.