Geochemical
Signature of Contaminated sediment Remobilization Revealed by Spatially
Resolved X-ray Microanalysis of Annual Rings of Salix nigra
TRACY
PUNSHON, PAUL M. BERTSCH, ANTONIO LANZIROTTI, KEN MCLEOD, AND JOANNA BURGER
Consortium for Risk Evaluation With Stakeholder Participation,
Environmental and Occupational Health Sciences Institute, Division of
Life Sciences, Rutgers University, 604 Allison Road, Piscataway, New Jersey
08854,
Savannah River Ecology Laboratory, University of Georgia, Drawer E, Aiken,
South Carolina 29802, and Consortium for Advanced Radiation Sources, The
University of Chicago, 5640 S. Ellis Avenue, Chicago, Illinois 60637
An X-ray microprobe was used to determine the concentration and distribution of Ni, U, and other metals within annual rings of willows (Salix nigra L.) from a former de facto radiological settling basin (Steed Pond; SP) and a depositional environment downstream (Tims Branch; TB) on the Savannah River Site (SRS). Geochemical and historical information about both areas are well documented. Following spillway breaches at SP in 1984 and the early 1990s, TB is inundated with contaminated sediments during storms. Bulk elemental composition of tree cores was determined using ICP-OES. Synchrotron X-rayfluorescence (SXRF) analysis showed that the metal contents of SP and TB cores were an order of magnitude higher than those from a reference site. TB cores were enriched with Ni in 1984 and 1991, corresponding with SP spillway breaches (containing 790 mg kg-1 Ni in 1991). Cores from SP exhibited an extremely high Ni peak in 1996, approximately 5000 mg kg-1, even though contaminant levels at SP did not change. The geochemical signature of contaminants recorded in TB annual rings reflected the significant sediment remobilization events consistent with the detailed history of the site, and at concentrations relative to their proximity to the source term. However, physiological processes occurring within impacted trees strongly influence the chronological accuracy of dendroanalysis and must be investigated further.
SREL Reprint #2675
Punshon, T., P. M. Bertsch, A. Lanzirotti, K. W. McLeod and J. Burger. 2003. Geochemical signature of contaminated sediment remobilization revealed by spatially resolved X-ray microanalysis of annual rings of Salix nigra. Environmental Science & Technology 37:1766-1774.
