Spectrochimica Acta Part B: Atomic Spectroscopy | 2019
Uranium quantification of oak tree rings (Quercus petraea) from a former uranium mining site by High Resolution Inductively Coupled Plasma Mass spectrometry in Laser Ablation and Solution modes
Abstract
Abstract Tree ring proxies are employed in dendroanalysis as a valuable tool for evaluating past anthropogenic contamination. A wide variety of analytical methods are used to quantify tree ring content for a broad spectrum of chemical elements. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is often used to investigate element concentrations in the tree rings. However, several issues regarding the representativeness of laser ablation measurements for trace elements have to be addressed before definitive conclusions can be drawn. In this study, High Resolution (HR)-ICP-MS has been implemented to analyze the trace concentration of uranium (U) in annual growth rings of oak trees (Quercus petraea) using both laser ablation (LA) and solution modes. The three tree samples taken for the present study were located upstream (with respect to the hydrologic system) of a former uranium mine site at Rophin (Puy de Dome, France), where mining operations were performed between 1949 and 1958. According to the LA-HR-ICP-MS technique, two-dimensional quantitative (2D) mapping of uranium has developed to study the spatial distribution of uranium at the tree ring surface. A strong heterogeneity was observed, leading to an average uranium concentration with high uncertainty (50–66%). Pressed pellets of the standard reference material, NIST1570a spinach leaves and uranium doped cellulose powder were adopted as the uranium standards for quantification. No agreement was found between uranium concentrations measured after acid digestion and the values obtained by laser ablation. This comparison highlights the limitations of laser ablation technique; hence the solution mode should be preferred for quantifying uranium trace concentrations in tree rings. However, low uncertainty (