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10.3 Remediation Strategies

Remediation is essential to mitigate the negative effects caused by the heavy metals
incorporated to ecosystems, alone or in mixtures. The overall objective of any soil
remediation approach is to create a final solution that protects human health and the
environment. Natural remediation of heavy metal-contaminated soils can be
improved by immobilization techniques.

10.3.1 Immobilization Techniques

Ex situ and in situ immobilization techniques are practical approaches to remedia-
tion of metal-contaminated soils.
The ex situ technique is useful in areas where a large amount of contaminated
soil must be removed from its place of origin, and its storage is connected with a
high ecological risk. The main advantage of ex situ techniques is the fast and
easy applicability. However, the disadvantages include (1) high invasivity to the
environment, (2) generation of a significant amount of solid wastes (twice as large
as volume after processing), (3) the by-product must be stored on a special landfill
site, (4) in the case of changing of the physicochemical condition in the side product
or its surroundings, there is serious danger of the release of additional contaminants
to the environment, and (5) permanent control of the stored wastes is required. Soil
remediation by conventional physicochemical technologies could be expensive;
there is an interest in alternative remediation strategies.
In in situ technique, the fixing agent’s amendments are applied on the
unexcavated soil. The technique’s advantages are (1) low invasivity, (2) simplicity
and rapidity, (3) relatively inexpensive, (4) small amount of wastes are produced,
(5) high public acceptability, and (6) envelop a wide spectrum of inorganic
pollutants. The disadvantages of in situ immobilization are as follows (1) is only
a temporary solution (contaminants are still in the environment), (2) the activation
of pollutants may occur when soil physicochemical properties change, (3) the
reclamation process is applied only to the surface layer of soil (30–50 cm), and
(4) permanent monitoring is necessary (USEPA 1995; Martin and Ruby 2004). In
situ immobilization technology often uses organic and inorganic amendment to
accelerate the attenuation of metal mobility and toxicity (Mench et al. 2006).
Specially, stabilization of contaminated soil by amendments or phytostabilization
is a remediation technique that reduces the mobile fraction of heavy metals, which
could contaminate groundwater or be taken up by soil organisms (Mench et al.
2000). In this respect, it is important remark that the study of solubility and
bioavailability might be more important in remediation activities than the study
of total or pseudo-total concentrations of these elements in contaminated soils,
because they represent the most labile fractions subject to leaching and to being
uptaken by plants and microorganisms (Adriano 2004).