In situ metal imaging and Zn ligand-speciation in a soil-dwelling sentinel:complementary electron microprobe and synchrotron microbeam x-ray analyses

Morgan, A. J. and Mosselmans, J. F. W. and Charnock, J. M. and Bennett, A. and Winters, C. and O'Reilly, M. and Fisher, P. and Andre, Jane and Turner, M. and Gunning, P. and Kille, P. (2013) In situ metal imaging and Zn ligand-speciation in a soil-dwelling sentinel:complementary electron microprobe and synchrotron microbeam x-ray analyses. Environmental Science and Technology, 47 (2). pp. 1073-1081. ISSN 0013-936X

Abstract

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.