Elemental line scanning of an increment core using EDXRF: From fundamental research to environmental forensics applications

Abstract

Environmental forensics seeks to determine the responsible parties for contamination from leaks or spills of petroleum or other toxic products. Dendrochemistry contributes to environmental forensics at the intersection of analytical chemistry, tree biology, and environmental responsibility. To be useful, dendrochemistry requires the rigorous application of analytical techniques as well as an understanding of tree biology. The choice of analytical technique is usually driven by tradeoffs among the selection of chemical elements or molecules of interest, sensitivity and discrimination, spatial resolution, ease of sample preparation, availability, sample destructiveness, and cost. One useful solid-state spectroscopic technique for dendrochemical analysis is energy dispersive X-ray fluorescence (EDXRF). This method provides essentially non-destructive, simultaneous detection of a number of elements with an adjustable spatial resolution, typically from 0.1 to 0.3 mm. The most commonly targeted elements are S and Cl as markers for fossil fuels, Cl for solvents, and Pb for leaded gasoline. Other metal elements may also be used as indicators of mining and smelting. For elements that are not normally present in appreciable amounts in wood, the mere presence of the element anywhere in the tree-ring record indicates exposure of the tree to an unusual chemical event or process. Dating the environmental exposure from dendrochemical analysis can be complicated by internal changes in tree chemistry due to wood infection, tree maturation, and wood maturation.