Our environment remains the victim of industrial growth. The number of recognized waste sites continues to grow daily (Panagos et al., 2013; Brombal et al., 2015; Carré et al., 2017). Past and continuing abuses require high remediation efforts in terms of technical, financial, and social resources. There is now international recognition of the problems of environmental damage, especially to soil. Land contamination is one of the eight threats mentioned in the EU Thematic Soil Strategy (European Commission, 2002), and is listed as one of the ten key threats that hamper the achievement of sustainable soil management (FAO, 2017). Managing soil pollution has been explicitly recognized as one of the needs to achieve sustainable development (UNEP, 2018). Accordingly, management and remediation of contaminated land is a rapid growth area for applications and technological innovations.
Cleaning up contaminated soils in an effective way is very difficult, even more so as it needs to be economically feasible at the same time. Increasingly, broader considerations with respect to overall environmental impact, long-term concerns, and sustainability further affect and change the way soil remediation is developing. Soil remediation and management of contaminated soil has evolved and matured over the past half-century toward promoting sustainable approaches that (Ellis and Hadley, 2009)
• Minimize consumption of energy or other natural resources
• Maximally avoid releases to the environment
• Harness or mimic natural processes
• Result in the reuse or recycling of land and materials
• Favor approaches that lead to effective destruction of contaminants
In many countries, the management of contaminated land has matured, and it is developing in many others. China, for example, recently has put a comprehensive policy and legislative framework in place (Li et al., 2015). In other countries, the process is yet to start (Sam et al., 2016; Arias Espana et al., 2018). This chapter aims to provide an overview of the issue of soil contamination and soil remediation approaches.
1.2 SOIL DEGRADATION AND SOIL CONTAMINATION
Natural soils in the environment are the result of thousands to millions of years of soil forming processes (Targulian and Krasilnikov, 2007). Time is one of the five major soil formation factors, next to climate, organisms, relief, and parent material (Jenny, 1994). As such, the natural soil is a unique resource that, once disturbed, cannot be reverted to a pristine state in the short term. In this sense it is non-renewable.
Soils provide numerous services to humanity. Soils are a substrate for biomass production, providing food, fodder, renewable energy, and raw materials. These functions are the basis of human and animal life (Blum, 2005). Soil has important filtering, buffering, and transformation capacities, providing a stable environment for supporting life functions, and largely contributing to the quality of air, food, and water, and thus to human health (Carré et al., 2017). It is a biological habitat for a large variety of organisms and thus hosts a large gene reserve. Soil is the physical support for human activities, and provides a source for raw materials such as clay, gravel, sand, and minerals. Humanity must move to a truly sustainable use of the soil as a limited resource.
Soil degradation refers to a decrease of the soil’s actual or potential capability to produce quantitative and qualitative goods and services as a result of degradative processes. These degradation processes may be of physical, chemical, or biological nature (Lal and Stewart, 2012). Compaction and hardsetting, laterization, and erosion/desertification by wind and/or water deteriorate the physical properties of the soil. A decline of organic matter and reduction of soil biological life reflect biological soil degradation. Chemical soil degradation is related to depletion of nutrients/fertility and establishment of imbalances in chemical composition. Contamination with toxic compounds is but one of the several threats to soil quality, and its remediation is the scope of this book.
Chemical contaminants are emitted into the environment by human activities related to mining, urbanization, industry, and agriculture (Horta et al., 2015). In Europe, waste disposal and treatment has been estimated to account for 37% of the contaminated sites, followed by industrial and commercial activities (33.3%), storage (10.5%), and transport spills on land (7.9%) (Panagos et al., 2013). Local contamination occurs when inadequate handling of wastes or accidents during human activities introduces excessive contaminants in the soil. Diffuse contamination is defined where the relationship between the contaminant source and the level and spatial extent of soil contamination is indistinct (Jones et al., 2012). Dispersed sources and transformation and dilution in other environmental compartments may have occurred before the contaminants ended up in the soil over wider areas and typically in more moderate concentrations.
The number of contaminated and potentially contaminated sites has been estimated at about 10 to 20 million worldwide (Carré et al., 2017) (Table 1.1). About 60% of contamination in soils in Europe is by metals (34.8%) and petroleum hydrocarbons (23.8%). Contamination with CHC (8.3%), BTEX (10.2%), and PAH (10.9%) constitutes another 30% of soil contamination cases (Panagos et al., 2013) (Figure 1.1). Although many countries actioned on their urgent sites, overall progress of remediation is slow. In the European Union, 5% of all identified sites were cleaned up in 2013. In Australia, the progress is at a rate of 5% per year. However, each year, about 5% new sites are identified. The United States had 1322 superfund sites in 2014. These are the most severely contaminated sites that are being monitored at the federal level. While 375 sites were cleaned up, 53 new sites were proposed for being designated superfund sites (Horta et al., 2015; Carré et al., 2017).
Soil remediation may entail substantial costs. In 2011, total costs for remediation of a site in Europe ranged from less than 5000 € to more than 50,000,000 €. More than 40% of the remediation cases costed between 50,000 and 500,000 € for site investigation and remediation (Figure 1.2) (Van Liedekerke et al., 2014). These costs may be offset in the longer term by the revalorization of the cleaned land and added value of the remedial actions. Remediation can create opportunities for recycling materials and potentially energy recovery. Revalorization of contaminated derelict land may create a wide range of beneficial opportunities including renewable energy, renewable feedstocks, water resource improvement, flood capacity and drainage management, carbon management, and societal benefits from amenity land and landscaping (Bardos et al., 2000; Dickinson et al., 2009; Bardos et al., 2011; Cundy et al., 2016).
