Plutonium(VI) accumulation and reduction by lichen biomass: correlation with U(VI)

Area of Science:

• Environmental science
• Radiochemistry
• Mycology

Background:

• Lichens are sensitive bioindicators of environmental contamination.
• Understanding radionuclide uptake by lichens is crucial for terrestrial ecosystem assessment.
• Plutonium (Pu) and Uranium (U) are key actinide contaminants of concern.

Purpose of the Study:

• To investigate the uptake mechanisms and migration behavior of plutonium (Pu) and uranium (U) in the foliose lichen Parmotrema tinctorum.
• To determine the influence of lichen biomass on the speciation and distribution of Pu and U in terrestrial environments.

Main Methods:

• Incubation of P. tinctorum with Pu(VI) and U(VI) solutions at varying pH.
• Quantification of radionuclide uptake using gravimetric analysis.
• Microscopic analysis using Scanning Electron Microscopy (SEM).
• Spectroscopic analysis using UV/VIS absorption spectroscopy to determine oxidation states.

Main Results:

• P. tinctorum exhibited significant uptake of both Pu and U.
• Pu accumulated on lichen surfaces, while U distributed within cortical and medullary layers.
• Pu(VI) was reduced to Pu(V) in solution and to Pu(IV) upon accumulation on the lichen.
• U(VI) maintained its oxidation state, indicating different interaction mechanisms.

Conclusions:

• Lichen uptake and reduction of Pu(VI) significantly influence Pu mobilization and speciation in terrestrial ecosystems.
• The low solubility of Pu(IV) hydroxides limits Pu penetration into lichen tissues.
• Parmotrema tinctorum's biological activity plays a critical role in controlling plutonium's environmental fate.