Accumulation of Tc-99 in duckweed Lemna minor L. as a function of growth rate and Tc-99 concentration

This study focuses on the question of whether short-term studies can be use d to forecast the accumulation of the long-lived fission product Tc-99 in d uckweed, Lemna minor L., grown in the field, in other words, are the accumu lation parameters independent of changing growth rates typical of natural p opulations of duckweed. Two processes determine the 99Tc accumulation: (i) uptake and release of (TcO4-)-Tc-99, characterised by a concentration facto r, K-d, and (ii) first-order reduction and complexation of Tc-VII, characte rised by k(red). At various Tc-99 concentrations, the growth, total Tc and TcO4- accumulation were monitored over 10 days; parameters were fitted and compared with earlier results. Both K-d and k(red) turn out to be independe nt of time, concentration and growth rate up to a concentration Of 10(-6) m ol l(-1 99)TcO(4)(-). Concentrations above this level result in toxic effec ts. The Tc accumulation in field populations of duckweed at Tc concentratio ns which generally occur in the environment can be forecasted by using the results from short-term experiments. (C) 2001 Elsevier Science Ltd. All rig hts reserved.