There are very few practical demonstrations of the phytoextraction of metals and metalloids from soils and sediments beyond small-scale and short-term trials. The two approaches used have been based on using 1) hyperaccumulator species, such as Thlaspi caerulescens (Pb, Zn, Cd, Ni), Alyssum spp. (Ni, Co), and Pteris vittata (As) or 2) fast-growing plants, such as Salix and Populus spp. that accumulate above-average concentrations of only a smaller number of the more mobile trace elements (Cd, Zn, B). Until we have advanced much more along the pathway of genetic isolation and transfer of hyperaccumulator traits into productive plants, there is a high risk in marketing either approach as a technology or stand-alone solution to clean up contaminated land. There are particular uncertainties over the longer-term effectiveness of phytoextraction and associated environmental issues. Marginally contaminated agricultural soils provide the most likely land use where phytoextraction can be used as a polishing technology. An alternative and more useful practical approach in many situations currently would be to give more attention to crops selected for phytoexclusion: selecting crops that do not translocate high concentrations of metals to edible parts. Soils of brownfield, urban, and industrial areas provide a large-scale opportunity to use phytoremediation, but the focus here should be on the more realistic possibilities of risk-managed phytostabilization and monitored natural attenuation. We argue that the wider practical applications of phytoremediation are too often overlooked. There is huge scope for cross-cutting other environmental agenda, with synergies that involve the recovery and provision of services from degraded landscapes and contaminated soils. An additional focus on biomass energy, improved biodiversity, watershed management, soil protection, carbon sequestration, and improved soil health is required for the justification and advancement of phytotechnologies.

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SUMMARYNine different clones of six species of Salix (Salix cordata Muhlenb. non Michaux, 5. fragilis L., S. caprea L., S. cinerea h., S. burjatica Nazarov. and 5. viminalis L.) and one hybrid (S. x calodendron Wimm.) were exposed to heavy metals in solution culture in an attempt to increase innate metal resistance. Resistance was estimated using comparative root measurements, and metal uptake was also studied. The first experiment entailed pretreatments with background nutrient solution, or 0-25 and 050 mg Cu 1"^ amendments, and re-exposure to each of the same concentrations. In a second experiment clones were exposed to sub-toxic concentrations of single metals (0-15 mg Cu 1"', O-lSmgCdl"' or 2-5mgZnl'') and dual-combination treatments (0-075mgCu|-'-l-0-O75mgCdl-', O'O75 mg Cu 1"'+ 1 25 mg Zn I"' or 0'075 mg Cd 1"'+ 1-25 mg Zn 1" = )' with concentrations gradually raised 10-fold over 128 d. Plants tested in the first experiment, following pre-exposure to Cu, were no more resistant to subsequent exposure to this metal. In the second experiment, gradual cumulati^ e doses resulted in reduced phytotoxicity and increased resistance, most notably to Cd. There appeared to be an inverse relationship between metal uptake and resistance. Copper uptake was restricted to the roots, whereas Cd and Zn were more evenly distributed throughout the plant. Exposure to dual combinations of metals resulted in several interaction effects on uptake: increased root-bound Cu in all combinations, and the increase in uptake of both Cd and Zn into the root tissues when supplied with Cu. The implications of these results for the use of willows in phytoremediation programmes are discussed.