How Do Radionuclides Accumulate in Marine Organisms? A Case Study of Europium with Aplysina cavernicola

Abstract

In the ocean, complex interactions between natural and anthropogenic radionuclides, seawater, and diverse marine biota provide a unique window through which to examine ecosystem and trophic transfer mechanisms in cases of accidental dissemination. The nature of interaction between radionuclides, the marine environment, and marine species is therefore essential for better understanding transfer mechanisms from the hydrosphere to the biosphere. Although data pertaining to the rate of global transfer are often available, little is known regarding the mechanism of environmental transport and uptake of heavy radionuclides by marine species. Among marine species, sponges are immobile active filter feeders and have been identified as hyperaccumulators of several heavy metals. We have selected the Mediterranean sponge Aplysina cavernicola as a model species for this study. Actinide elements are not the only source of radioactive release in cases of civilian nuclear events; however, their physicochemical transfer mechanisms to marine species remain largely unknown. We have targeted europium(III) as a representative of the trivalent actinides such as americium or curium. To unravel biological uptake mechanisms of europium in A. cavernicola, we have combined radiometric (γ) measurements with spectroscopic (time-resolved laser-induced fluorescence spectroscopy, TRLIFS, and X-ray absorption near-edge structure, XANES) and imaging (transmission electron microscopy, TEM, and scanning transmission X-ray microscopy, STXM) techniques. We have observed that the colloids of NaEu(CO)·nHO formed in seawater are taken up by A. cavernicola with no evidence that lethal dose has been reached in our working conditions. Spectroscopic results suggest that there is no change of speciation during uptake. Finally, TEM and STXM images recorded at different locations across a sponge cross section, together with differential cell separation, indicate the presence of europium particles (around 200 nm) mainly located in the skeleton and toward the outer surface of the sponge.

Uranium Uptake in Paracentrotus lividus Sea Urchin, Accumulation and Speciation

“…13 Ku et al reported similar values with a mean concentration of uranium of about 3.3 µg/L. 14 Altogether uranium represents about 1% of the total radioactivity in seawater (the major contributor being 40 K accounting for more than 90%). 15 In seawater, the accumulation of several heavy metals in marine organisms has been widely studied at all trophic levels.…”

“…39 The STXM methodology employed in this study was similar to that described previously. [40][41] The photon energy calibration of the monochromator was performed at the neon K-edge (867.3 eV). The STXM measurements were performed with a 25 nm zone plate in transmission mode and the ALS was operating in top-off mode with a beam current of 500 mA.…”

Sponges are highly resistant to radiation exposure and cancer

“…For these reasons sponges are considered biological indicators of environmental pollution such as radionucleotides 37,38 .…”

The Adsorption of Europium and Uranium on the Sodium Dodecyl Sulfate Modified Molybdenum Disulfide Composites

“…With the rapid development of nuclear energy, the safe treatment and disposal of nuclear waste have restricted the further development of the nuclear industry. As one of the common radionuclide contaminants, uranium (U) mainly results from nuclear fuel production, which has been released into the ecological environment. − Because of its long half-life, europium (Eu) is also considered to be a hazardous radioactive contaminant. , The accumulation and storage of a large volume of radioactive waste in the environment can be a threat to human health and result in various diseases due to its potential toxicity and carcinogenesis. , Therefore, many methods such as coagulation, electrodeposition, adsorption, reverse osmosis, and solvent extraction have been used for the elimination of radionuclides from the environment. − Among these techniques, adsorption is a low cost and environmental friendly method, and a variety of adsorbents including activated carbon and clay mineral have been applied to remove radionuclides. , For example, the adsorption of U­(VI) on the layered double hydroxide/graphene material achieved 277.80 mg/g, showing a great advantage . Nevertheless, most of the existing studies only pay attention to the elimination of a single pollutant and neglect the existence of other radionuclides.…”

“…4,5 The accumulation and storage of a large volume of radioactive waste in the environment can be a threat to human health and result in various diseases due to its potential toxicity and carcinogenesis. 6,7 Therefore, many methods such as coagulation, electrodeposition, adsorption, reverse osmosis, and solvent extraction have been used for the elimination of radionuclides from the environment. 8−11 Among these techniques, adsorption is a low cost and environmental friendly method, and a variety of adsorbents including activated carbon and clay mineral have been applied to remove radionuclides.…”