MAPPING URANIUM AND LEAD CONTAMINATION THROUGH THE ISOTOPIC ANALYSIS OF TREES

Cores taken from black oak (Quercus velutina) were used to map the spatial distribution of air and waterborne contamination of an isotopically distinct form of uranium (depleted uranium) emanating from an industrial facility in West Concord, Massachusetts. Isotope dilution thermal ionization mass spectrometry allows for the identification and measurement of the natural and anthropogenic components of uranium and lead present in sapwood and bark samples; sapwood is demonstrated to monitor the uptake of contaminants from near surface water while bark monitors atmospheric contamination. The highest depleted uranium concentrations in sapwood come from samples that are immediately down gradient from the manufacturing facility, following known groundwater flow vectors. Similarly, the highest concentrations of depleted uranium in bark samples are found down wind from the site. Depleted uranium is present in bark samples over a far greater area than sapwood samples and is also present across hydrologic boundaries. The isotopic composition of lead appears to reflect mixing between anthropogenic lead and bedrock-derived sources. Lead isotopic compositions in bark are similar to published data for atmospheric lead in New England, whereas sapwood samples are considerably more radiogenic. Likewise, bark lead concentrations are an order of magnitude higher than sapwood concentrations.

Analysis of wood and bark samples from birch, hemlock, maple and pine are being performed in order to determine whether these species may also be useful for monitoring contamination. These parallel studies of isotopically distinct uranium and lead offer promise that 1) trees may be suitable monitors of trace element air and waterborne contamination, and 2) uptake pathways of contaminants within trees can be determined.