Speciation of americium in seawater and accumulation in the marine sponge Aplysina cavernicola

Abstract

The fate of radionuclides in the environment is a cause of great concern for modern society, seen especially in 2011 after the Fukushima accident. Among the environmental compartments, seawater covers most of the earth's surface and may be directly or indirectly impacted. The interaction between radionuclides and the marine compartment is therefore essential for better understanding the transfer mechanisms from the hydrosphere to the biosphere. This information allows for the evaluation of the impact on humans via our interaction with the biotope that has been largely undocumented up to now. In this report, we attempt to make a link between the speciation of heavy elements in natural seawater and their uptake by a model marine organism. More specifically, because the interaction of actinides with marine invertebrates has been poorly studied, the accumulation in a representative member of the Mediterranean coralligenous habitat, the sponge Aplysina cavernicola, was investigated and its uptake curve exposed to a radiotracer (241)Am was estimated using a high-purity Ge gamma spectrometer. But in order to go beyond the phenomenological accumulation rate, the speciation of americium(III) in seawater must be assessed. The speciation of (241)Am (and natural europium as its chemically stable surrogate) in seawater was determined using a combination of different techniques: Time-Resolved Laser-Induced Fluorescence (TRLIF), Extended X-ray Absorption Fine Structure (EXAFS) at the LIII edge, Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy and Scanning Electron Microscopy (SEM) and the resulting data were compared with the speciation modeling. In seawater, the americium(III) complex (as well as the corresponding europium complex, although with conformational differences) was identified as a ternary sodium biscarbonato complex, whose formula can be tentatively written as NaAm(CO3)2·nH2O. It is therefore this chemical form of americium that is accumulated by the sponge A. cavernicola.

Experimental Speciation of Plutonium(IV) in Natural Seawater

“…Previously, this method was successfully applied to the study of uranium, neptunium and americium in natural seawater. X‐ray Absorption Spectroscopy (XAS) was performed together with Time Resolved Laser Fluorescence Spectroscopy for uranium(VI) ,…”

Molecular dynamics simulations of Y(iii) coordination and hydration properties

“…Reiller et al 15,16 performed inductive analysis of the existing migration law of Am and associated it with rare-earth elements; they concluded that when the pH of the solution is less than 7, between 7 and 8.5, and above 8.5, the main complex ions are RE 3+ , RECO 3 + and RE(CO 3 ) 2 À , and possibly RE(CO 3 ) 3 3À or higher-valence-state complex ions, respectively. Given similarities in the physicochemical properties of Am and rareearth elements, Maloubier et al 17 investigated the results of Am migration studies and concluded that the main forms of rare-earth carbonate ions in a water environment with pH 7-9 are RECO 3 + and RE(CO 3 ) 2…”

Determining Metal Ion Complexation Kinetics with Fluorescent Ligands by Using Fluorescence Correlation Spectroscopy

“…This typically involves sample volumes of ca. 1 ml at concentrations around 10 −6 M or larger . As an example, for the actinide 241 Am such a sample has a radioactivity of ∼31 kBq (taking into account a specific activity of 3.43 Ci/g).…”