2015 GSA Annual Meeting in Baltimore, Maryland, USA (1-4 November 2015)

Paper No. 107-5
Presentation Time: 9:00 AM-6:30 PM


CARLSON, Timothy, MCHUGH, Kelly C. and WIDOM, Elisabeth, Department of Geology and Environmental Earth Science, Miami University, Oxford, OH 45056, carlsotr@miamioh.edu

The Mound site in Miamisburg, Ohio was opened in 1946 by the Department of Energy for atomic weapons research and development. The site expanded to include facilities that supported energy, weapons, and space missions. During operation, metals and radioisotopes such as Po, Pu, Th, and U were released and deposited in the local soil and groundwater due to poor waste containment and improper materials handling. The facility was designated a superfund site in 1989, shut down in 1996; remediation started in 1997. This study tests modern lichen as an indicator of the spatial distribution of past airborne contamination. Lichen absorb all nutrients directly from the air, hence they provide records of the spatial extent of airborne particulate dispersal. Seven lichen samples were collected within 2.3 km of the Mound site, most in the dominant downwind direction. Ashed lichen contain high abundances of Pb (149-727 ppm) and Ti (5-176 ppm); many metals (As, Mo, Sn, REE) show decreasing concentrations with distance from the site. Pb in the lichen is most likely sourced from the urban industrial area surrounding the laboratories (this may also be the source of Ti). Despite U and Th being handled on site for nuclear weapons and energy research, low concentrations of U (0.23-1.17 ppm) and Th (0.62-3.03 ppm) were detected in the ashed lichen samples. However, TIMS analysis of U isotopic compositions in the lichen indicate the presence of non-natural U in the environment, with 235U/238U = 0.00726 - 0.00732, 236U/238U = 4.42E-08 – 6.17E-06, and 234U/238U activity ratios = 0.88 - 1.03. Though large additions of anthropogenic U are required to modify 235U/238U, the minor isotopes of U, especially 236U, are sensitive to minute additions of non-natural U. Positive correlations between U concentrations and 236U/238U as well as 234U/238U provide cryptic evidence that enriched U was released into the area surrounding the Mound Site. These results further illustrate that lichen can be used for detection and tracking spatial distributions of contaminants.