Bacteria need chemical resistance for nuclear remediation

Scientists from the Los Alamos National Laboratory have found that bacteria used for remediation of nuclear waste contamination, need to be resistant to chemical pollution rather than radioactivity, if they are to be truly successful.

Bacteria are already widely used to remediate contaminated land, and have been known to break down nuclear material (see related story). This research may well make their use far more widespread, particularly for land contaminated with actinides and other radionuclides.

Published in the journal Environmental Microbiology, the research shows that actinides - elements with an atomic number above 89 and usually radioactive - produce primarily chemical, rather than radiological, toxicity. Therefore, a bacteria's resistance to radiation does not necessarily mean they will be tolerant to radionuclides. In fact, the things that would affect the bacteria's performance the most may well be other toxic metals rather than the radioactive elements.

The study also shows that, when it comes to these environmental bacteria, plutonium is less toxic than uranium, and, in general, actinides are less toxic than other types of metals.

"This study is exciting because even though we've known for years that bacterial bioremediation can be a preferred method for cleaning up actinide contamination, we've never really known whether or not radioactivity or chemical toxicity will stifle the process," said Mary Neu, one of the Los Alamos team who conducted the study. "Our study found that actinides are chemically toxic to bacteria only at high levels far, far above concentrations at contaminated sites, and that common toxic metals, such as cadmium, nickel and chromium, are more likely to cause problems for the bacteria."

In most cases, bacteria used for bioremediation are selected to target a specific form and oxidation state of toxic pollutants, such as soluble hexavalent uranium carbonate for uranium contamination. However, a single chemical rarely contaminates soils and groundwater, and combinations of actinides, radionuclides, organic chemicals and metal regularly exist at many nuclear sites.

Based on the results of this study, if bioremediation is to be effective at these types of sites, the operative micro-organisms must be able to grow, function and do better than other bacteria in the presence of all kinds of contaminants.

Source: Los Alamos National Laboratory.




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