USE OF DENDROCHEMISTRY TO EVALUATE ELEMENT UPTAKE IN BLACK WALNUT TREES GROWING ON A COAL WASTE PILE IN INDIANA

A dendrochemistry study was conducted to evaluate temporal changes in trace metal uptake at an abandoned coal mine site in western Indiana. Tree cores were collected from five black walnut trees growing on a coal waste pile and also from five black walnut trees at an uncontaminated control site located four km upgradient, with respect to groundwater flow and prevailing wind direction, from the mine site. Each tree was cored twice to ensure accuracy in cross dating. Three samples were extracted from each core at prescribed five-year intervals (i.e., year intervals of 1960-1964, 1978-1982, and 1996-2000), representing early, middle, and late growth. The samples were dissolved and resulting solutions were analyzed by inductively coupled plasma mass spectrometry for 28 elements, including those commonly associated with coal waste products. We were able to quantify elements with concentrations as low as one ppb.

Preliminary results reveal that Si, Ca, K, Mg, Fe, Cu, Zn, Ni, Sr, Ba, Mn, Cr, Al, Rb, Ga, Co, V, and Tl (in decreasing order of abundance) are present in the tree rings at concentrations higher than the limit of quantitation (LOQ). Whereas, Ag, As, Cd, Cs, Li, Pb, Se, and U are at concentrations below the LOQ. The preliminary data show that there is little variability in trace element concentrations between the sampled trees growing at the study site. In addition, the data indicate no significant differences in the concentrations of most trace elements from early to late growth. Several elements do show a minor decrease in concentration in the middle time interval. This decrease coincides with a known drought period that overlaps the sampling time interval. In general, the results indicate that the bioavailability of these elements has not changed significantly during the life span of the trees.