Exploring Americium bioaccumulation in Ascophyllum nodosum seaweed through Europium as a surrogate: A kinetic and speciation study

Studies of metallic radionuclides in oceans represent an important field of research. Because of their direct impact on marine ecosystems, they are especially important for assessing environmental health and safety. The high chemical – and radio – toxicity of heavy actinide elements makes them a particular threat to organisms, regardless of isotopy. Among these, americium is well known for its strong biosorption potential and combined chemo – radiotoxic effects. This study investigates the bioaccumulation of ²⁴¹Am and of ¹⁵³Eu (stable) and ¹⁵²Eu as its chemical surrogate, in the brown macroalga Ascophyllum nodosum. Environmental analogies between ¹⁵²Eu and ²⁴¹Am are discussed, validating Europium as a reliable homolog in this system. Biokinetic accumulation models across trace and ultra-trace concentration levels are reported showing consistent behavior within the data, with a mono-exponential saturation pattern best fitting. Alginate was identified as a primary chelating agent, with speciation studies revealing potential alginate – Europium complexes in algal tissues. These findings highlight the essential role of algal polysaccharides in the uptake of metallic radionuclides and provide an entry into the ecological risk assessment associated with marine ecosystem contamination.