Phytotoxicity testing of lysimeter leachates from aided phytostabilized Cu-contaminated soils using duckweed (Lemna minor L.).

Aided phytostabilization of a Cu-contaminated soil was conducted at a wood preservation site located in southwest France using outdoor lysimeters to study leaching from the root zone and leachate ecotoxicity. The effects of Cu-tolerant plants (Agrostis gigantea L. and Populus trichocarpa x deltoides cv. Beaupré) and four amendments were investigated with seven treatments: untreated soil without plants (UNT) and with plants (PHYTO), and planted soils amended with compost (OM, 5% per air-dried soil weight), dolomitic limestone (DL, 0.2%), Linz-Donawitz slag (LDS, 1%), OM with DL (OMDL), and OM with 2% of zerovalent iron grit (OMZ). Total Cu concentrations (mgkg(-1)) in lysimeter topsoil and subsoil were 1110 and 111-153, respectively. Lysimeter leachates collected in year 3 were characterized for Al, B, Ca, Cu, Fe, Mg, Mn, P, K and Zn concentrations, free Cu ions, and pH. Total Cu concentration in leachates (mgL(-1)) ranged from 0.15±0.08 (LDS) to 1.95±0.47 (PHYTO). Plants grown without soil amendment did not reduce total Cu and free Cu ions in leachates. Lemna minor L. was used to assess the leachate phytotoxicity, and based on its growth, the DL, LDS, OM and OMDL leachates were less phytotoxic than the OMZ, PHYTO and UNT ones. The LDS leachates had the lowest Cu, Cu(2+), Fe, and Zn concentrations, but L. minor developed less in these leachates than in a mineral water and a river freshwater. Leachate Mg concentrations were in decreasing order OMDL>DL>PHYTO=OM=LDS>UNT=OMZ and influenced the duckweed growth.