Biokinetics of Americium-241 in the euryhaline diamond sturgeon Acipenser gueldenstaedtii following its uptake from water or food

Abstract

Americium-241 whole body and internal biokinetics were experimentally investigated in the euryhaline diamond sturgeon Acipenser gueldenstaedtii during its uptake from water and food, in fresh (FW) and brackish water (BW; 9 psu). Whole-body uptake rates of ²⁴¹Am from water and subsequent depuration rates were quantified over 14 and 28 days, respectively, and assimilation efficiency (AE) of ²⁴¹Am from diet (chironomid) was determined over 28 days. FW reduced the biological half-life of ²⁴¹Am following aqueous uptake by an order of magnitude. In contrast BW greatly reduced ²⁴¹Am assimilation efficiency (AE) from diet (chironomid) by several orders of magnitude (from an AE of 8.5% (FW) down to 0.003% (BW)). Hence, salinity per se is indicated as a major environmental variable in determining the radiological exposure of A. gueldenstaedtii to ²⁴¹Am. During aqueous exposure BW appreciably increased ²⁴¹Am activity concentrations in most body components, but aqueous or dietary exposure pathway at either salinity did not determine marked differences in how ²⁴¹Am was distributed among six body components. The highly mineralized skin of A. gueldenstaedtii recurred as a major repository of ²⁴¹Am in all experimental treatments, as high as 50% among body components, due to its internal transfer from diet, surface adsorption and/or active absorption from water. The indicated prominence of the aqueous, compared to the dietary, exposure pathway for ²⁴¹Am accumulation by A. gueldenstaedtii suggests its radiological exposure would be enhanced by BW as it leads to its greater long-term retention, due to a much longer biological half-life.