Analysis of metal deposit distribution in ants (Crematogaster scutellaris) at the Florence external scanning microbeam

Metals are one of the major classes of environmental contaminants and raise concerns for their adverse effects on ecosystems. Ants are good candidates as bioindicators for metal contamination assessment; previous studies indeed showed that ants are able to selectively accumulate some metals within their tissues. Available works provide only whole-body burdens of these contaminants, with scarce information on the fine-scale localisation in tissues and organs, although this information is important to better understand the behaviour of metals in living organisms and to clarify their effects in ecosystems. At the Florence external scanning microbeam, we are carrying on a Particle Induced X-ray Emission (PIXE) study on a common ant species sampled from sites with different environmental metal availabilities. Measurements were carried out on resin-embedded, self-standing sections for a direct localisation of metal deposits and an easy determination of their content. The combined use of the PIXE and the external scanning microbeam made it possible to map element distributions with good spatial resolution and sensitivity, restricting quantitative analyses to the metal accumulation regions. To determine in which tissues/organs metals concentrated, we compared PIXE maps with histological images on sections contiguous to the analysed slices. Measurements in the external set-up allowed us to avoid sample damaging. Differences in metal concentrations in ants from different sites resulted from quantitative PIXE analyses.