UO22+ speciation determines uranium toxicity and bioaccumulation in an environmental pseudomonas sp. isolate

Abstract

In the present study, experiments were performed to investigate how representative cellulosic breakdown products, when serving as growth substrates under aerobic conditions, affect hexavalent uranyl cation (UO22+ ) toxicity and bioaccumulation within a Pseudomonas sp. isolate (designated isolate A). Isolate A taken from the Cold Test Pit South (CTPS) region of the Idaho National Laboratory (INL), Idaho Falls, ID, USA. The INL houses low-level uranium-contaminated cellulosic material and understanding how this material, and specifically its breakdown products, affect U-bacterial interactions is important for understanding UO22+ fate and mobility. Toxicity was modeled using a generalized Monod expression. Butyrate, dextrose, ethanol, and lactate served as growth substrates. The potential contribution of bicarbonate species present in high concentrations was also investigated and compared with toxicity and bioaccumulation patterns seen in low-bicarbonate conditions. Isolate A was significantly more sensitive to UO22+ and accumulated significantly more UO 22+ in low-bicarbonate concentrations. In addition, UO22+ growth inhibition and bioaccumulation varied depending on the growth substrate. In the presence of high bicarbonate concentrations, sensitivity to UO22+ inhibition was greatly mitigated, and did not vary between the four substrates tested. The extent of UO22+ accumulation was also diminished. The observed patterns were related to UO22+ aqueous complexation, as predicted by MINTEQ (ver. 2.52) (Easton, PA, USA). In the low- bicarbonate medium, the presence of positively charged and unstable UO 22+ -hydroxide complexes explained both the greater sensitivity of isolate A to UO22+ , and the ability of isolate A to accumulate significant amounts of UO22+ . The exclusive presence of negatively charged and stable UO22+ -carbonate complexes in the high bi-carbonate medium explained the diminished sensitivity of isolate A to UO22+toxicity, and limited ability of isolate A to accumulate UO22+. © 2010 SETAC.