THE POSSIBILITY OF IN-SITU HEAVY-METAL DECONTAMINATION OF POLLUTED SOILS USING CROPS OF METAL-ACCUMULATING PLANTS

The decontamination of soils and wastes polluted with heavy metals pre sents one of the most intractable problems for soil clean-up. Present technology relies upon metal extraction or immobilization processes, b oth of which are expensive and which remove all biological activity in the soil during decontamination. They may only be appropriate for sma ll areas of valuable redevelopment land. In this paper the use of meta l-accumulating plants is explored for the removal of metals from super ficially-contaminated soils such as those resulting from the long-term application to land of metal-contaminated sewage sludges. Green remed iation employs plants native to metalliferous soils with a capacity to bioaccumulate metals such as zinc and nickel to concentrations greate r than 2% in the aerial plant dry matter (hyperaccumulators). Growing such plants under intensive crop conditions and harvesting the dry mat ter is proposed as a possible method of metal removal and for 'polishi ng' contaminated agricultural soils down to metal concentrations below statutory limits. Not only are the biological activity and physical s tructure of soils maintained but the technique is potentially cheap, v isually unobtrusive and offers the possibility of biorecovery of metal s. The limitations of the process are reviewed and the future requirem ents for the development of efficient phytoremediators are outlined.