**1. Introduction**

Over two centuries of various anthropogenic emissions have caused soil contamination to be a globally widespread problem, involving not only industrialized countries but even remote areas of less developed countries [1]. From decision makers to scientists and even to individual

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

citizens, all generally accept and understand that air and water pollution can have negative impacts on human health [2–4]. However, the same statement concerning soil pollution is harder to understand [5]. In the vast majority of papers or books that deals with the problem of soil pollution, the traditional approach is to isolate a single variable, such as a specific contaminant, and then investigate that variable as its source, fate, distribution and/or health effect [6]. Nonetheless, it is difficult to accept that, after 200 years of industrialization and intensive agriculture, rural and urban soil are only mono-contaminated. It is more than probable that in any contaminated soil horizon, more than one pollutant is present [7]. Among the most common harmful contaminants are heavy metals (37%) and mineral oils (33%), along with a large variety of persistent organic pollutants (known as POPs). Scientists and members of the medical professions are acknowledging that environmental and health effects due to soil multiple contamination present complicated issues due to synergistic relationships [8].

Almost all manuscripts that presented soil decontamination techniques have a similar approach: identification of a single pollutant and subsequent treatment. Moreover, the vast majority of these studies generally use a clean soil spiked with the chosen compound. The general reason given for not using genuine contaminated soil is often the same: since it is known that many remediation processes belong to either phyto- [9] or bioremediation [10] families, the authors wanted to avoid interferences with their own method. However, such procedures may be valuable in diminishing or even completely eliminate a particular pollutant, but in the probable case of multiple contaminations it would mean a multiple treatment of the polluted soil. Moreover, most of these treatment methods are still on the laboratory or on the ex situ scale [11]. This renders most of the laboratory-scale treatment inapplicable because of ultimately high costs: the same soil should be treated in various ways, according to each particular pollutant present [12, 13].

The general assessment criteria for the selection of the proper remediation technology are:


Thus, in order to diminish the costs of a treatment procedure applied to contaminated soils, an obvious solution would be to have *in situ* treatment instead of an ex situ one (completely removing the cost of transportation and relocation of soil). A good number of such processes are also known nowadays [14–17].

There are various ways to consider the most appropriate way to treat a contaminated soil [11]. These are the following: (1) doing nothing (if the environmental assessment indicates that humans and the environment are not at risk, then no remediation activity is required, e.g., in the case of small-scale spills on sites where human and animal exposure is not likely), (2) introducing institutional controls to contain the contaminants in the infected area (a legal or institutional mechanism that limits the use or the access to the contaminated area, e.g., the Chernobyl or Fukushima areas) or (3) the removal of soil and/or destruction of contaminants

(in some cases, the best option may be to physically remove the contaminated soil and move it to a special treatment, storage and disposal facility; in other cases, it is possible to remove the contaminant from the soil using technologies such as surfactant washing, soil washing or thermal desorption). Ultimately, the contaminants are destroyed, on condition that the byproducts are not toxic.

The *in situ* technologies are categorized into three major groups based on the primary mechanism by which the treatment is achieved:


citizens, all generally accept and understand that air and water pollution can have negative impacts on human health [2–4]. However, the same statement concerning soil pollution is harder to understand [5]. In the vast majority of papers or books that deals with the problem of soil pollution, the traditional approach is to isolate a single variable, such as a specific contaminant, and then investigate that variable as its source, fate, distribution and/or health effect [6]. Nonetheless, it is difficult to accept that, after 200 years of industrialization and intensive agriculture, rural and urban soil are only mono-contaminated. It is more than probable that in any contaminated soil horizon, more than one pollutant is present [7]. Among the most common harmful contaminants are heavy metals (37%) and mineral oils (33%), along with a large variety of persistent organic pollutants (known as POPs). Scientists and members of the medical professions are acknowledging that environmental and health effects due to soil multiple contamination present complicated issues due to synergistic relationships [8]. Almost all manuscripts that presented soil decontamination techniques have a similar approach: identification of a single pollutant and subsequent treatment. Moreover, the vast majority of these studies generally use a clean soil spiked with the chosen compound. The general reason given for not using genuine contaminated soil is often the same: since it is known that many remediation processes belong to either phyto- [9] or bioremediation [10] families, the authors wanted to avoid interferences with their own method. However, such procedures may be valuable in diminishing or even completely eliminate a particular pollutant, but in the probable case of multiple contaminations it would mean a multiple treatment of the polluted soil. Moreover, most of these treatment methods are still on the laboratory or on the ex situ scale [11]. This renders most of the laboratory-scale treatment inapplicable because of ultimately high costs: the same soil should be treated in various ways, according to

The general assessment criteria for the selection of the proper remediation technology are:

– the reduction in mass or volume of the contaminants (preferably their complete eradication);

Thus, in order to diminish the costs of a treatment procedure applied to contaminated soils, an obvious solution would be to have *in situ* treatment instead of an ex situ one (completely removing the cost of transportation and relocation of soil). A good number of such processes

There are various ways to consider the most appropriate way to treat a contaminated soil [11]. These are the following: (1) doing nothing (if the environmental assessment indicates that humans and the environment are not at risk, then no remediation activity is required, e.g., in the case of small-scale spills on sites where human and animal exposure is not likely), (2) introducing institutional controls to contain the contaminants in the infected area (a legal or institutional mechanism that limits the use or the access to the contaminated area, e.g., the Chernobyl or Fukushima areas) or (3) the removal of soil and/or destruction of contaminants

each particular pollutant present [12, 13].

234 Soil Contamination - Current Consequences and Further Solutions

– the cost-effectiveness.

are also known nowadays [14–17].

– the short-term versus long-term effectiveness in remediation;

– the overall reduction of the toxicity of previously contaminated soil; and

– Thermal

Physical/chemical treatment includes soil vapour extraction, solidification/stabilization, soil flushing, chemical oxidation and electrokinetic (EK) separation. Biological treatment uses microorganisms or vegetation to degrade, remove or immobilize pollutants in soil. Biological technologies include bioventing, phytoremediation and monitored natural attenuation. Electrical resistivity heating, steam injection and extraction, conductive heating, radiofrequency heating and vitrification are technologies summarized under thermal treatment.

The past few years saw an increase in the number of *in situ* treatment technologies that are effectively used in the field (e.g. chemical oxidation [18] or thermal treatment [19]), demonstrating thus that *in situ* technologies are a viable option for treating contaminated soils.

Yet, in order to have a truly useful as well as an economical process, the technology should be able to eliminate more than only one contaminant, simultaneously, since it is obvious that mono-pollution is an utopian case. For example, the soils of abandoned agricultural land contaminated by e-waste activities in Hong Kong listed no less than four classes of pollutants (polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, polybrominated diphenyl ether compounds and heavy metals—cadmium, copper, chromium, lead and zinc) [20]. Fortunately, in the last few years, such methods made an interesting appearance in the environmental science and engineering literature. In the following, we review some of these dual decontamination methodologies that deal simultaneously with at least one organic and one inorganic contaminant in the same soil matrix.
