Speciation-Dependent Toxicity of Neptunium(V) Toward Chelatobacter heintzii

Abstract

This work investigates how chemical speciation controls the toxicity of neptunium and the neptunium−NTA complex toward Chelatobacter heintzii. We studied the effect of aquo and complexed/precipitated neptunium on the growth of C. heintzii in noncomplexing glucose and phosphate-buffered nitrilotriacetic acid (NTA) growth media. Equilibrium chemical speciation modeling and absorption spectroscopy were used to link neptunium speciation to biological growth inhibition. Our results show that metal toxicity of aquo NpO2 + significantly limits the growth of C. heintzii at free metal ion concentrations greater than ≈10-5 M. However, neptunium concentrations ≥10-4 M do not cause measurable radiotoxicity effects in C. heintzii when present in the form of a neptunium−NTA complex or colloidal/precipitated neptunium phosphate. The neptunium−NTA complex, which is stable under aerobic condi tions, is destabilized by microbial degradation of NTA. When phosphate was present, degradation of NTA led to the precipitation of a neptunium-phosphate phase.

Subsurface bio-mediated reduction of higher-valent uranium and plutonium

“…In our research [8,4,[16][17][18], we also have shown that neptunyl, as NpO 2 + , is reduced in a wide variety of anaerobic systems. Methanogens and sulfate reducers actively precipitate neptunium from solution, and this was confirmed to be due to bioreduction to form Np(IV) precipitates by XANES analysis.…”

Experimental study of neptunyl adsorption onto Bacillus subtilis

“…Np(IV) also is generally less soluble than Np(V), (Lemire et al, 2001) and both of these properties suggest that the mobility of Np(IV) is considerably lower than that of Np(V) in the subsurface. To date, most Np-related geomicrobiological research has focused on the microbial reduction of Np(V) to Np(IV) (Banaszak et al, 1998;Banaszak et al, 1999;Lloyd et al, 2000;Soderholm et al, 2000;Rittmann et al, 2003). Np(V) adsorption onto bacterial cell walls has received relatively little attention.…”

Adsorption of Pb(II) and Eu(III) by Oxide Minerals in the Presence of Natural and Synthetic Hydroxamate Siderophores

“…These highly toxic radioactive elements are known to form strong complexes with biological ligands that affect both their sorption by soil minerals and their uptake by microorganisms (2,3). Otherwise, in the absence of competing ligands, their sorption to metal oxides, clay minerals, and soil or sediment solids is strong (4)(5)(6)(7).…”