Metal-accumulating woody species have been considered for phytoextraction of metal-contaminated sites. We investigated Zn and Cd accumulation in tissues of adult trees and associated herbaceous ...species collected from contaminated areas in Central Europe. We found considerable Cd and Zn accumulation in various willow, poplar and birch species with up to 116
mg
Cd
kg
−1 and 4680
mg
Zn
kg
−1 in leaves of
Salix caprea. Annual variation of Cd and Zn concentrations in leaves of
Salix caprea were small, indicating that data obtained in different years can be compared. Metal concentrations in leaves were not related to total (
aqua regia) or labile (1
M NH
4NO
3 extract) concentrations in soil but the accumulation factors (leaf concentration: soil concentration) for Cd and Zn followed an inverse log type function. Metal partitioning between tissues showed a minimum in the wood, with increasing concentrations of Cd and Zn towards the leaves and fine roots.
Adult field-grown Salix caprea, Populus tremula and other tree species accumulate up to 4680
mg
Zn
kg
−1 and 116
mg
Cd
kg
−1 in their leaves.
Phytoextraction is an emerging technology for non-destructive remediation of heavy metal-polluted soils. This study was conducted to test chelate-assisted phytoextraction of Cu, Pb and Zn using EDTA ...and canola (Brassica napus L. cv. Petranova) on a moderately polluted industrial soil (loamy sand) in the sub-continental climate of Eastern Austria. The effects of the rate (up to 2.1 g kg-1 soil) and mode (single versus split) of EDTA application on the biomass, water contents and metal concentrations in shoots and roots were investigated along with changes of metal lability in soil and leaching from the root zone in parallel outdoors pot and lysimeter experiments. Labile (1 M NH4NO3-extractable) metal concentrations in soil increased considerably upon application of EDTA, indicating enhanced phytoavailability. However, this was also associated with enormously increased metal concentrations in the leachates collected below the root zone. Enhanced metal labilities and leachate concentrations persisted for more than 1 year after harvest. Metal lability was more enhanced by EDTA in rhizosphere relative to bulk soil, indicating interactions of EDTA with root activities. Shoot biomass and water contents of canola were virtually unaffected by EDTA, revealing that canola can tolerate excessive metal concentrations in soil pore water. Metal concentrations in shoots were increased considerably, but were insufficient to obtain reasonable extraction rates. Split applications were generally more effective than the same amounts of EDTA added at once. Metal concentrations in roots decreased after each application of EDTA, possibly indicating metal removal from roots by free protonated EDTA, but increased again within several days. As the application of chelate-assisted phytoextraction is limited by the risk of groundwater pollution, further work should focus on natural, continuous phytoextraction technologies.
Sorption curves are commonly used to predict the partitioning of ions between the soil solid and solution in ion transport and rhizosphere models. We review methods for measuring metal desorption for ...such purposes, and we illustrate the problems involved by means of measurements of Ni desorption from a contaminated soil as an example. We find that measurements of metal concentration in shaken soil suspensions at a range of solution:soil ratios give similar desorption curves to the more tedious method of repeated extraction at a constant, smaller and therefore more realistic solution:soil ratio. We also find that desorption is sensitive to the nature and concentration of the background electrolyte used, and to interactions between these and additions of organic chelating agents of the sort excreted by roots and rhizosphere microbes.
