Page 286 - Plant-Based Remediation Processes

280 G. Petruzzelli et al.

· Further growing cycles Extraction with
· Further chemical mild extractant
extraction to evaluate 4 Verification of the to determine metals
residual bioavailable absence of 1 Evaluation of in soil pore water
metals bioavailable metal bioavailable
metals

3 Growth of plants 2 Assessment
treated with of the potential
mobilising agents release of metals
from soil surface
Determination of metals Extraction
concentration in by mobilising agents
plants and leachates specific for each metal

Fig. 13.1 Enhanced bioavailable contaminant stripping scheme

quality, which is not uncommon at contaminated sites. In addition, the plant growth
may highlight the root-induced changes affecting metal bioavailability (Hinsinger
and Courchesne 2008).
The EBCS approach shown in Fig. 13.1 can be subdivided into four steps:

1. Evaluation of the metal in a potentially bioavailable form. Soluble or easily
solubilizable amounts are identified (i.e., the exchangeable species).
2. Determination of the total amount of long-term extractable metal over time. This
step is performed making use of metal-specific mobilizing agents. Since the
action of the mobilizing agent is much greater than any natural process, the
amount determined in this step can be considered (based on a precautionary
approach) as the maximum quantity of metals available to plants.
3. Growth of plants in pot experiments, in order to select the most efficient species
on the basis of their ability to take up both the original and the newly created
available fractions, which are brought into solution by the specific mobilizing
agent. Control of the possible presence of metals in the leachates from pot trials.
4. After harvesting, further cycles of plant growth are performed on the same soils,
with and without the addition of the specific mobilizing agent, in order to control
the absence of residual metals in bioavailable forms. An extraction with the
specific additive is carried out on soil to verify the absence of mobile chemical
forms of the metallic element. When the metal concentration in plants is
negligible and no amount of metal can be extracted from the soil by the specific
mobilizing agent, the residual concentration of metal can be considered to be
permanently unavailable.