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

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 Am from water and subsequent depuration rates were quantified over 14 and 28 days, respectively, and assimilation efficiency (AE) of Am from diet (chironomid) was determined over 28 days. FW reduced the biological half-life of Am following aqueous uptake by an order of magnitude. In contrast BW greatly reduced Am 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 Am. During aqueous exposure BW appreciably increased Am activity concentrations in most body components, but aqueous or dietary exposure pathway at either salinity did not determine marked differences in how Am was distributed among six body components. The highly mineralized skin of A. gueldenstaedtii recurred as a major repository of Am 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 Am 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.