Detection of biological uranium reduction using magnetic resonance

Area of Science:

• Environmental science
• Microbiology
• Geochemistry

Background:

• Subsurface uranium contamination poses environmental risks.
• Bacterial reduction of U(VI) to U(IV) is a promising immobilization strategy.
• Iron and sulfate-reducing bacteria facilitate uranium transformation.

Purpose of the Study:

• To investigate magnetic resonance (MR) relaxation times (T₁ and T₂) of uraninite.
• To quantify the impact of uraninite properties on MR signals.
• To assess the feasibility of using MR for monitoring uranium bioremediation.

Main Methods:

• Bacterial reduction of uranyl ions (UO₂²⁺) to uraninite (UO₂(s)) using Shewanella putrefaciens CN32.
• Magnetic resonance imaging (MRI) techniques including gradient echo and spin echo.
• Experiments in liquid suspension, polysaccharide gel, and in situ bioreactors with varying mixing conditions.

Main Results:

• T₁ and T₂ relaxation times showed dependence on uranium oxidation state and solubility.
• Magnetic field fluctuations (T*₂) from uraninite particles and uranyl ions were quantified.
• A reduction in T₂ was observed in a polysaccharide gel simulating biofilm.
• Quantifiable T₂ magnetic relaxation effects were detected in bioreactors over the reaction time.

Conclusions:

• Magnetic resonance imaging is a viable tool for monitoring uranium bioremediation.
• Uraninite properties significantly influence MR relaxation times.
• Understanding these effects aids in developing effective strategies for immobilizing subsurface uranium contamination.