Extensive environmental and health impacts studies have been car- ried out on FA, which contains trace and heavy metals. They can readily percolate down from conventionally used earth-lined ash lagoons and pol- lute groundwater. Effect of FA on groundwater is a function of physical and chemical characteristics of ash and hydrogeologic and climatic con- ditions of the disposal site (Ciccu et al., 2003; Goetz, 1983; Kopsick and Angino, 1981; Kumpiene et al., 2007). Weathered FA deposits cause more groundwater contamination because of the presence of higher levels of sol- uble salts. In unweathered ash, although there is generally a higher release of soluble salts initially, it declines rapidly with time (Hjelmar, 1990; Jones and Lewis, 1960; Kopsick and Angino, 1981; Mattigod et al., 1990; Theis et al., 1978).
FA, particularly when it has been dry collected and handled, contains moderate-to-high levels of soluble salts, primarily sulphates and borates.
Dissolution of these salts into soil solution can generate high levels of salts, which can suppress plant growth or actually kill salt-sensitive seedlings and/
or established vegetation (Adriano et al., 2002). This behavior is referred to as phytotoxicity, and generally decreases drastically once the ash-bound salts are leached away by rainfall. The soluble salt content of CCPs or CCPs- treated soil is measured by an assessment of the electrical conductance over a water extract. Under strongly acidic conditions (<pH 5.0), ash-bound heavy metals such as Al, Mn, Zn and Cu can also come into solution and become phytotoxic (Daniels et al., 2002). Therefore, application of CCPs mainly depends on the pH of the amended soil (Seshadri, 2011; Fig. 6.9).
For example, when the soil pH raises above 8.5 after amending with CCPs, fertilizer P applied to soil can be retained and precipitated in the soil. Simi- larly, when pH falls below 6.5, mobilization of some of the heavy metals (native or CCPs-derived) may take place and can result in toxic effects to plants. Under such a scenario, phytomining can be a potential option for the environmental management of CCPs in soil. At optimal pH (6–7), the use of CCPs in soil encourages agricultural applications, especially in terms of effective phosphorus management (Figs 6.8 and 6.12).
Very little is known regarding the effects of CCPs amendment on soil biological properties (Schutter and Fuhrmann, 2001). Few studies have been conducted on the size, activity and nature of the microbial community on
Figure 6.12 Schematic representation on pH-based risk management approaches in the utilization of CCPs.
ash disposal sites. All of the factors discussed above (viz. high pH, salinity, toxicities of B and other elements, poor physical conditions) can limit colo- nization of microorganisms as well as plants in the ash (Carlson and Adriano, 1993). Even so, by far, the most limiting factors for microbial activity are often a lack of substrate C as an energy source for heterotrophic microor- ganisms and the lack of an adequate N supply (Klubek et al., 1992).
Several short-term laboratory incubation studies found that addition of unweathered FA to sandy soils severely inhibited microbial respiration, enzyme activity and soil nitrogen cycling processes such as nitrification and N mineral- ization (Cervelli et al., 1987; Garau et al., 1991; Gupta et al., 2012; Pitchel and Hayes, 1990; Topaỗ et al., 2008; Wong and Wong, 1986). Adriano et al. (2002) reported that at higher levels of FA, some heavy metals might become more active and hinder microbial activity. These metals form complexes, which undergo transformation, influenced by various factors like pH, moisture, cat- ion exchange and microbial activity (Milovsky and Kononov, 1992).
Generally, the FA particles are small enough to escape emission control devices and easily get suspended in the air. Repeated exposure to FA can cause irritation in eyes, skin, nose, throat and respiratory tract and result in As poisoning (Belkin et al., 1999; Carlson and Adriano, 1993; Davison et al., 1974; Finkelman et al., 2000; Natusch and Wallace, 1974). Fine ash particles formed during coal combustion in power stations, if not collected in the air pollution control devices are emitted into the atmosphere. The fine ash particles can remain airborne for long periods and can result in deleterious health effects when inhaled and deposited in the lungs (Buhre et al., 2005).
Harrison and Yin (2000) conducted epidemiological studies on FA par- ticulate matter exposure and consistently demonstrated adverse effects on human health, the mechanism of effect was unclear. Depending on their toxicity, chemical properties and concentration in the air, FA particles may pose an inhalation hazard to exposed workers. When FA particles are inhaled and deposited in the lung, they can impose health risks by leach- ing genotoxic compounds, and through the alteration of immunological mechanisms. Studies have indicated that exposure to high concentrations of fine particulate matter may not be the sole contributor to these adverse effects, but that particle toxicology could also play an important role (Har- rison and Yin, 2000). The emissions of fine ash particles and trace (toxic) elements from coal combustion are closely associated because of the relative enrichment in trace elements of these fine particles (Lighty et al., 2000).
Although the fine particles are enriched in trace elements, their composi- tion is not determined by these elements. Coal composition is shown to
be an important parameter affecting the amount and composition of the submicron ash particles (Buhre et al., 2005).
Toxic heavy metals from CCPs are likely to be leached under acidic conditions. These metals can be easily taken up by humans through drink- ing water supplies, causing severe health problems:
• Lead—brain, kidney, and nervous system damage • Cadmium—high blood pressure, liver damage, cancer • Mercury—deterioration of the nervous system • Arsenic—carcinogenic
Arsenic is classified as a Class A human carcinogen (US EPA), and is at the top of the most hazardous substances list (ATSDR, 1997). Viriyavejakul and Watanasak (2003) evaluated carcinogenic risks of As present in CCPs and observed that As levels are within the acceptable limits. They also related the potential human health risk with the distance from the contaminated site and concluded that health risk decreased with the distance away from the site.
In vitro studies show that CCPs independent of type of coal combus- tion, origin or precipitation are capable of exerting cytotoxicity in a num- ber of conventional tests using either animal lung cells, human red blood cells or cell lines such as hamster ovary cells (Borm, 1997). Dogra et al.
(1995) demonstrated that inhaling CCPs may result in an impairment of the local immune response of the lungs without an associated effect on the systemic immunity. They have shown that phagocytosis and adherence of alveolar macrophages, as well as the appearance of antibody forming cells in lymph nodes were moderately but significantly affected by in vivo exposure to both FA and silica (Dogra et al., 1995).
In general, CCPs are less toxic than crystalline silica (when used as posi- tive control) but significantly more toxic than negative controls (TiO2, latex beads, methacrylate polymers). McDonald et al. (2001) observed strong association between silicosis and lung cancer in silica-exposed cohorts, demanding a careful evaluation of the health effects of CCPs containing considerable amount of silica.