Uptake of polonium and sulfur by bacteria

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Abstract
Elevated concentrations of polonium‐210, the last radioactive member of the 238U decay series, have been reported for groundwater in a number of shallow wells from the Central Florida Phosphate District. The 210Po must originate either directly from the naturally occurring phosphate rock of the area or from phosphogypsum, a byproduct of the wet‐process manufacture of phosphoric acid. Phosphate rock is characterized by relatively high levels of uranium and daughter products, while phosphogypsum contains high 226Ra, 210Pb, and 210Po. We assessed the potential of a bacterial isolate to remove and incorporate dissolved polonium from solution by conducting comparative radiotracer experiments using 35SO4 and 208Po. Since the observed chemical concentration of Po in these wells is too low to serve in any direct metabolic function, it was suspected that it might be cometabolized as a sulfur analogue. Our experiments were designed to (1) evaluate the rate of 33SO4 and 208Po uptake as a function of bacterial growth, and (2) fractionate the bacteria into various cellular components to determine how polonium and sulfur were partitioned within the cell. Results indicated that while the initial uptake mechanisms for 33SO4 and 208Po differ, once associated with the bacterial cells, polonium is dispersed between the cell walls, cytoplasm, and protein in a manner similar to sulfur. The bacterial uptake rate of polonium is sufficiently rapid that the potential exists for development of a bioremediation scheme for removal of polonium (and perhaps other ions) from contaminated aqueous solutions.