Geomicrobiology of High-Level Nuclear Waste-Contaminated Vadose Sediments at the Hanford Site, Washington State

Authors

James K. Fredrickson, Pacific Northwest National LaboratoryFollow
John M. Zachara, Pacific Northwest National LaboratoryFollow
David L. Balkwill, Florida State University
David Kennedy, Pacific Northwest National LaboratoryFollow
Shu-mei W. Li, Pacific Northwest National Laboratory
Heather M. Kostandarithes, Pacific Northwest National Laboratory
Michael J. Daly, Uniformed Services University of the Health Sciences
Margaret F. Romine, Pacific Northwest National Laboratory
Fred J. Brockman, Pacific Northwest National Laboratory

Date of this Version

2004

Citation

Applied and Environmental Microbiology, 70(7); pp. 4230–4241, (July 2004)

Abstract

Sediments from a high-level nuclear waste plume were collected as part of investigations to evaluate the potential fate and migration of contaminants in the subsurface. The plume originated from a leak that occurred in 1962 from a waste tank consisting of high concentrations of alkali, nitrate, aluminate, Cr(VI), ¹³⁷Cs, and ⁹⁹Tc. Investigations were initiated to determine the distribution of viable microorganisms in the vadose sediment samples, probe the phylogeny of cultivated and uncultivated members, and evaluate the ability of the cultivated organisms to survive acute doses of ionizing radiation. The populations of viable aerobic heterotrophic bacteria were generally low, from below detection to ~10⁴ CFU g^-1, but viable microorganisms were recovered from 11 of 16 samples, including several of the most radioactive ones (e.g., >10 µCi of ¹³⁷Cs/g). The isolates from the contaminated sediments and clone libraries from sediment DNA extracts were dominated by members related to known gram-positive bacteria. Gram-positive bacteria most closely related to Arthrobacter species were the most common isolates among all samples, but other phyla high in G+C content were also represented, including Rhodococcus and Nocardia. Two isolates from the second-most radioactive sample (>20 µCi of ¹³⁷Cs g^-1) were closely related to Deinococcus radiodurans and were able to survive acute doses of ionizing radiation approaching 20 kGy. Many of the gram-positive isolates were resistant to lower levels of gamma radiation. These results demonstrate that gram-positive bacteria, predominantly from phyla high in G+C content, are indigenous to Hanford vadose sediments and that some are effective at surviving the extreme physical and chemical stress associated with radioactive waste.