Abstract

A wide gamut of environmental and health issues of high societal impact benefit from analytical techniques which can characterize elemental abundances and chemical speciation in minute samples that are heterogeneous at the submicrometer scale. High-intensity, highly focused X-ray probes, so-called hard X-ray microprobes (HXRM), have had a major impact in advancing our understanding of the speciation, transport, and reactions of chemical species in these spatially heterogeneous materials. X-ray microprobe techniques offer distinct advantages over other analytical techniques by allowing analyses to be done in situ, an important example being the ability to determine chemical speciation of a wide variety of toxic elements in moist soils and biological specimens with little or no chemical pretreatment and with low detection limits (ppm and ppb). In particular, coupled microfocused X-ray fluorescence, spectroscopy, and diffraction analysis allows researchers to quantify the abundance and speciation of trace elements in these and simultaneously evaluate the mineralogy to which they are adsorbed or bound. Modern HXRM instruments also allow for these analyses to be done as imaging experiments, not only in two dimensions but three dimensionally (3D) using tomographic techniques. Such information is crucial in understanding the toxicity, mobility, and containment of contaminating metals in the environment, mechanisms of trace element partitioning, and paths of strategic metal enrichment in nature. This presentation will provide a brief overview of the GSECARS 13-ID-E HXRM instrument at the Advanced Photon source and provide some examples of how researchers have used these methods in environmental and biological sciences.

Figure 1. X‐ray fluorescence compositional map of the posterior section of Lumbricus terrestris Linnaeus, the common earthworm. This is from a study by Seiter et al. (2012), with an emphasis on understanding the biogenic formation of metal‐rich granules in earthworms from Pb‐enriched soils. Shown are fluorescence intensities for Ca Kα (red), Zn Kα (green) and Pb Lα1 (blue). The image covers an area 2.35 × 2.06 mm in size and consists of 1.2 megapixels. Pixel size is 2 μm with 10 ms accumulation time per pixel. The Pb‐rich areas in the earthworm digestive system shown in blue are where Pb has accumulated in biogenically formed metal‐rich granules. The Zn‐enriched areas at the earthworm margins in green are Zn localized in setae, growths on earthworm segments used for locomotion.