USE OF XRF SPECTROMETRY TO ANALYZE METAL CONCENTRATIONS IN TREE CORES

X-ray fluorescence spectrometry (XRF) offers a potentially nondestructive method of analyzing metal concentrations in tree cores. If metals are immobile once emplaced in tree rings, a ring-by-ring analysis presents a unique opportunity to study both the temporal and spatial extent of contamination in a forested area. Idaho's Silver Valley is a reasonable place to test the applicability of XRF analysis of metals in tree cores. Mining in the Silver Valley began with the discovery of gold in 1883 and continued with the later discovery of silver, lead, and zinc-bearing ore, making the Silver Valley one of the richest mining regions in the country. Mines and mills dumped waste rock and tailings directly into the river or on steep hillsides. Smelting began in 1917, producing an even more toxic environment. Metal production in the Silver Valley peaked in the 1960's, and the Bunker Hill Complex was declared a Superfund Site in 1983. Contaminants remain in the system; lead, for example, is found in concentrations of tens of thousands of parts per million in stream sediment. Previous studies have shown that trees take up and sequester metals. A USGS LA-ICPMS study demonstrated that pine trees recorded a history of mine-related metal pollution in California. Analysis via LA-ICPMS is expensive and time-consuming, whereas XRF analysis is quick, cheap, and nondestructive. The question remains, however: does it produce accurate and repeatable results? Comparison of XRF and FAAS analyses of tree core segments reveals both consistencies and inconsistencies. Comparison of XRF analyses of unmodified tree cores, modified tree cores, and crushed tree cores indicates that sample condition influences test results.