Trees Preserve History of Contaminant Exposure


There is disagreement on whether analysis of annual rings from trees growing in contaminated areas provides information on a tree’s contaminant exposure history. Tracy Punshon at the University of Georgia’s Savannah River Ecology Laboratory (SREL) used synchrotron x-ray microanalysis at Brookhaven’s National Synchrotron Light Source on extracted cores from black willow trees to show that this past disagreement is due in part to an inability to determine the spatial distribution of metals in tree core samples. This novel analytic approach enables the study of the in situ distribution, concentration, and chemical binding environment of metals in environmental samples a far more informative technique than traditional wet-chemistry methods, which involve drying, grinding and digestion of samples in acids. Punshon’s work shows that trees from metal-contaminated areas do have a signature of metals in their annual rings that corresponds with historic information on the timing of contaminant exposure. However, a tree can only be used as an indicator of its contaminant history if it has not experienced excessive toxicity. Over time, trees can adapt to their environment, enabling them to avoid high-level pockets of contaminants, reducing the amount of contaminant they take up. Knowing this may help scientists to more accurately interpret tree ring data in the future.