Pb and Zn imaging and in situ speciation at the geogenic/biogenic interface in sentinel earthworms using electron microprobe and synchrotron micro-focus X-ray spectroscopy

Using synchrotron- and electron microscope-based X-ray microanalyses, the distribution and speciation of Zn and Pb were examined in situ in two earthworm species (Dendrodrilus rubidus and Lumbricus rubellus) living in heavily-polluted soils. Main findings: (i) Zn spectra in ingested soil and in tissues more closely resembled Zn-3(PO4)(2) than ZnS; (ii) Zn speciation in tissues gave a best fit for Zn to the inner shell of 4 oxygens at 1.94 angstrom (or nitrogens at 1.96 angstrom); (iii) the best fit for Pb in tissue was with a shell of oxygens at 2.18 angstrom and a shell of sulphurs at 2.67 angstrom; (iv) a component of the Zn and much of the Pb detectable in gut contents was co-distributed with S; (v) Zn and Pb display 'soft' acid affinities in soil, but 'hard' acid affinities in tissue. This is the first metal characterisation study conducted on an invertebrate quench-frozen in the field. (C) 2012 Elsevier Ltd. All rights reserved.