Microbial Community Composition Near Depleted Uranium Impact Points

Abstract

Military training activities can result in the deposition of depleted uranium (DU) into surface soils. Mechanisms of introduction include the generation of dust from firing and impact as well as the eventual corrosion of projectile fragments and unexploded ordnance. Microorganisms in surface soils have the potential to affect the transport of DU by direct binding of the metal to the cell surface, by altering near field soil chemistry that affects metal solubility, and by microbially influenced corrosion. We investigated the response (in terms of community composition) of a native soil microbiota to the presence of DU in an arid environment. Bacteria in soils outside of the test area were challenged in dilute media with “yellow cake” or U ₃ O ₈ . At concentrations of 200 to 20,000 mg L^{− 1} only species of Bacillus were identified. In situ characterizations (by PLFA analysis) of exposed site soils showed an enrichment in sulfate reducing bacterial (i17:1w7c up 39%) and Bacillus species (a15:0 up 35%) biomarkers. Three types of microbial communities were defined (as PLFA profiles) using exploratory statistics and related to three different levels of DU exposure. The community types were then statistically corresponded to site soil chemistry. Observed differences in site soil chemistry were attributed to munitions firing since enrichments (unexposed to exposed) were observed in the minerals magnesium (increase of ∼ 18 mg kg⁻¹ ), potassium (increase of ∼ 46 mg kg⁻¹ ) and sulfur (increase of ∼ 12 mg kg⁻¹ ), all constituents of munitions residues. Increased concentrations of these minerals corresponded with a community type that was associated with an area of extensive DU round use.

Keywords:

• Depleted Uranium (DU)
• munitions
• ester-linked polar lipid fatty acids (PLFA)
• microbial community composition.

We would like to thank Dr. Greg Ostrom, Mr. Lou Roncase, Mr. Ray Kelso, Mr. Gary Beckstrom and Mr. Matthew Jackson for their assistance in the collection, packaging, and safe shipment of the samples and Larry Perry and Karen Foley for their technical assistance in sample preparation. We would also like to thank our sponsor, the Naval Facilities Engineering Command, Washington, D.C., for funding this effort and Mr. Andy Del Collo, program manager for Environmental RDT&E, for his interest and input.

Notes

¹Tryptic Soy Broth.

²Peptone, Tryptone, Yeast Extract, Glucose.

³Microbial Identification Instrument (MIDI) similarity index (1 = perfect match).