Assessment of the hyperaccumulating lead capacity of Salvinia minima using bioadsorption and intracellular accumulation factors

Salvinia minima has been reported as a cadmium and lead hyperaccumulator being the adsorption and intracellular accumulation the main uptake mechanisms. However, its physicochemical properties, the effect of metal concentration and the presence of organic and inorganic compounds on its hyperaccumulating capacity are still unknown. Furthermore, the specific adsorption and accumulation mechanisms occurring in the plant are not clear yet. Thus, based on a compartmentalization analysis, a bioadsorption (BAF) and an intracellular accumulation factor (IAF) were calculated in order to differentiate and quantify these two mechanisms. The use of kinetic models allowed predicting the specific type of uptake mechanisms involved. Healthy plants were exposed to five lead concentrations ranging from 0.80 +/- 0.0 to 28.40 +/- 0.22 mg Pb(2+)l(-1) in batch systems. A synthetic wastewater, amended with propionic acid and magnesium sulfate, and deionized water were used as media. The BAF and IAF contributed to gain an in-depth insight into the hyperaccumulating lead capacity of S. minima. It is clear that such capacity is mainly due to adsorption (BAF 780-1980) most likely due to its exceptional physico-chemical characteristics such as a very high surface area (264 m(2) g(-1)) and a high content of carboxylic groups (0.95 mmol H(+)g(-1) dw). Chemisorption was predicted as the responsible mechanism according to the pseudo-second order adsorption model. Surprisingly, the ability of S. minima to accumulate the metal into the cells (IAF 57-1007) was not inhibited at concentrations as high as 28.40 +/- 0.22 mg Pb(2+)l(-1).