Evaluating the potential of native ureolytic microbes to remediate a ⁹⁰Sr contaminated environment

This study was a preliminary evaluation of ureolytically driven calcite precipitation and strontium coprecipitation for remediating ⁹⁰Sr contamination at the Hanford 100-N Area in Washington; in particular the approach is suitable for treating sorbed ⁹⁰Sr that could otherwise be a long-term source for groundwater contamination. Geochemical conditions at the site are compatible with long-term calcite stability, and therefore groundwater and sediment samples were examined to assess the ureolytic capabilities of the native microbiota. Quantitative assays detected up to 2 × 10⁴ putative ureC gene copies mL^-1 in water and up to 9 × 10 ⁵ copies g^-1 in sediment. The ureC assays and laboratory-based estimates of ureolytic activity indicated that the distribution of in situ ureolytic potential was very heterogeneous with depth and also that the ureolytic activity was predominantly associated with attached organisms. A mixed kinetic-equilibrium model was developed for the 100-N site to simulate urea treatment and predict strontium removal. Together, the microbial characterization data and modeling suggest that the site has the requisite biogeochemical characteristics for application of the calcite precipitation remediation approach for ⁹⁰Sr.