Elevated concentrations of actinides in mono lake

Area of Science:

• Geochemistry
• Environmental Science
• Radiochemistry

Background:

• Mono Lake, a saline and alkaline lake, exhibits unique water chemistry.
• Actinide concentrations in natural waters are typically low due to their insolubility.

Purpose of the Study:

• To investigate the elevated concentrations of certain actinides in Mono Lake.
• To determine the factors responsible for maintaining these actinides in solution.

Main Methods:

• Comparison of actinide concentrations in Mono Lake water with seawater.
• Analysis of actinide ratios (e.g., actinium/protactinium, americium/plutonium) to infer speciation and sources.
• Assessment of the role of natural ligands in actinide solubility.

Main Results:

• Tetravalent thorium, pentavalent protactinium, hexavalent uranium, and plutonium are significantly more concentrated in Mono Lake than in seawater.
• Trivalent actinides (actinium, americium) are not similarly enhanced, as indicated by low actinium/protactinium and americium/plutonium ratios.
• The elevated concentrations of insoluble actinides are attributed to complexation with natural ligands in the lake water.

Conclusions:

• Natural ligands play a crucial role in solubilizing and retaining normally insoluble actinides in Mono Lake.
• The high actinide concentrations are maintained by complexation, not by an exceptionally high rate of supply.
• Mono Lake serves as a unique natural laboratory for studying actinide behavior in aquatic environments.