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13 Phytoremediation Towards the Future: Focus on Bioavailable Contaminants 285

EBCS procedure, the potential gaseous loss of Hg(0) has been controlled (Mercury
tracker 3000IP Mercury Instruments GMBH) and the values were negligible. When
used at field scale, a monitoring program should be planned to control the absence
of transport of mercury in the deeper soil layer.
Since the natural processes of depletion and accumulation are not quantitatively
determinable in the short term, according to a precautionary principle we have
modified the BCS remediation approach by adding a new step, in which mercury
bioavailability was enhanced with the use of a mobilizing agent. In this way, the
amount of Hg releasable over time is considered. This amount is largely greater
than the one deriving from natural processes, and thus represents all the possible
available Hg that can be removed by plants (remediation target), while the
remaining Hg in soil can be safely considered unavailable. This hypothesis was
supported by results from the second growing cycle. If we move from current
definition of remedial targets based on total metal concentrations, EBCS appears
promising, since it removes the most dangerous metal forms while substantially
shortening the cleanup time, with an elevated security. After EBCS, the residue
metal in soil will remain unavailable over time, since it was not released in mobile
forms even with the use of strong mobilizing agents.

13.5 Concluding Remarks

The concept of soil quality has evolved in response to the increased demand for a
sustainable land use. It has been recognized that soil is essential for the environ-
ment, and new strategies must be defined for soil protection. Contamination is one
of the most important threats to soil quality and contaminated soils must be cleaned
up. However in remediation procedures, soil quality has often been considered only
marginally. The new trends in remediation strategies “Green Remediation” have
recovered the importance of soil quality. Green remediation technologies are
rapidly expanding in the world to reduce overall environmental impact of cleanup.
Green remediation is a completely new strategy of remediation that consider
environmental impacts of remediation activities at every stage of the remedial
process in order to maximize the net environmental benefit of a cleanup.
Considerations include selection of a remedy, energy requirements, efficiency of
on-site activities, and reduction of impacts on surrounding areas (USEPA 2008a).
Among the core elements of green remediation there is the aim to minimize the
bioavailability of contaminants by the use of minimally invasive technologies to
reduce soil and habitat disturbance. In this frame, the use of a solar-driven
biological technology such as phytoremediation as primary remedy or finishing
step is strongly recommended.
Considerable future research for the improvement of phytoremediation is still
necessary. Multidisciplinary efforts are needed to combine plant biology, soil
chemistry, and microbiology, as well as agricultural practices, but high efficiency
of phytoextraction will be obtained only if bioavailable contaminant is in contact