Chromium bioaccumulation: comparison of the capacity of two floating aquatic macrophytes.

The capacity of Salvinia herzogii and Pistia stratiotes to remove Cr (III) from water and their behaviour at different Cr (III) concentrations were studied in outdoor experiments. Cr distribution in aerial parts and roots with time and the possible mechanisms of Cr uptake were analyzed. Both macrophytes efficiently removed Cr from water at concentrations of 1, 2, 4 and 6 mgCrL(-1). S. herzogii was the best adapted species. At a greater initial concentration, greater bioaccumulation rates were observed. Root Cr uptake was a rapid process that was completed within the first 24h. Cr uptake through direct contact between the leaves and the solution is the main cause of the increase of Cr in the aerial parts, Cr being poorly translocated from the roots to the aerial parts. Both mechanisms were fast processes. The Cr uptake mechanism involves two components: a fast component and a slow one. The former occurs mainly due to the roots and leaves adsorption and is similar for both species. The slow component is different for each species probably because in P. stratiotes a Cr precipitation occurs induced by the roots.