high soil pH, the cations replace protons and get adsorbed to charged colloids so
tightly that they are not readily bioavailable (Olaniran et al. 2013). Transition (Fe,
Al, Zn, Cu, Cr, Ni, Mn, Pb and Co) as compared to alkaline earth cations has strong
tendency to get adsorbed onto charge colloids and form inner-sphere complexes
(Violante et al. 2010). Moreover, organic pollutants with low molecular weight
behold less adsorption capacity onto silicates in soil (Lin et al. 2015).
16.4.2.3 Hydrolysis of Inorganic/Organic Species in Solution
Sorption capacity of soil increases with increasing soil pH and vice versa (Paulose
et al. 2007). The lower the pH value, the more organic and inorganic elements can be
found in solution. Soil pH catalyzes the hydrolysis reaction and subsequently
influences degradation of pesticides, atrazine and inorganic salts (Zhang et al. 2013).
16.4.2.4 Dissolution of Inorganic/Organic Complexing Anions
High soil pH lowers high solubility of dissolve organic carbon and base cation
concentrations, whereas low pH enhances their solubility in soil (Olaniran et al.
2013). Several studies have reported a positive correlation between pH and retention
of Cd, Pb, Cu and Zn in soil (Deurer and Bottcher 2007).
16.4.3 Soil Organic Matter
Soil organic matter can reduce or increase the bioavailability of pollutants in soil
through immobilization or mobilization by forming various insoluble or soluble
complexes, respectively (Shrestha et al. 2019). A wide range of organic acids
(formic, acetic, oxalic, succinic, malonic, maleic, citric, malic, lactic, fumaric acids
and aconitic) acts as ligands for many cations in soil (Vranova et al. 2013;
Fijałkowski
et
al.
2012).
Generally,
citric
acid
followed
by
malic>acetic>tartaric>oxalic acid is the most effective in terms of desorption of
different metals (Zn, Cu, Hg, Pb, caesium (Cs) and Cd) in soil due to more carboxyl
group to form stable ligand (Köchy et al. 2015).
16.4.4 Cation Exchange Capacity
Cation exchange capacity (CEC) of soils depends upon soil types, amounts and
types of different colloids (Harter and Naidu 2001). Clayey soils have higher CEC
value (30 cmol kg
-1
) compared to sandy soils (< 5 cmol kg
À1 ). Similarly, humus has
very high CEC value compared to the inorganic clays (i.e., kaolinite). Thus, the
greater the CEC value, more is the exchange sites on soil minerals for organic and
inorganic species.
16 Causes, Effects and Sustainable Approaches to Remediate Contaminated Soil
461
tightly that they are not readily bioavailable (Olaniran et al. 2013). Transition (Fe,
Al, Zn, Cu, Cr, Ni, Mn, Pb and Co) as compared to alkaline earth cations has strong
tendency to get adsorbed onto charge colloids and form inner-sphere complexes
(Violante et al. 2010). Moreover, organic pollutants with low molecular weight
behold less adsorption capacity onto silicates in soil (Lin et al. 2015).
16.4.2.3 Hydrolysis of Inorganic/Organic Species in Solution
Sorption capacity of soil increases with increasing soil pH and vice versa (Paulose
et al. 2007). The lower the pH value, the more organic and inorganic elements can be
found in solution. Soil pH catalyzes the hydrolysis reaction and subsequently
influences degradation of pesticides, atrazine and inorganic salts (Zhang et al. 2013).
16.4.2.4 Dissolution of Inorganic/Organic Complexing Anions
High soil pH lowers high solubility of dissolve organic carbon and base cation
concentrations, whereas low pH enhances their solubility in soil (Olaniran et al.
2013). Several studies have reported a positive correlation between pH and retention
of Cd, Pb, Cu and Zn in soil (Deurer and Bottcher 2007).
16.4.3 Soil Organic Matter
Soil organic matter can reduce or increase the bioavailability of pollutants in soil
through immobilization or mobilization by forming various insoluble or soluble
complexes, respectively (Shrestha et al. 2019). A wide range of organic acids
(formic, acetic, oxalic, succinic, malonic, maleic, citric, malic, lactic, fumaric acids
and aconitic) acts as ligands for many cations in soil (Vranova et al. 2013;
Fijałkowski
et
al.
2012).
Generally,
citric
acid
followed
by
malic>acetic>tartaric>oxalic acid is the most effective in terms of desorption of
different metals (Zn, Cu, Hg, Pb, caesium (Cs) and Cd) in soil due to more carboxyl
group to form stable ligand (Köchy et al. 2015).
16.4.4 Cation Exchange Capacity
Cation exchange capacity (CEC) of soils depends upon soil types, amounts and
types of different colloids (Harter and Naidu 2001). Clayey soils have higher CEC
value (30 cmol kg
-1
) compared to sandy soils (< 5 cmol kg
À1 ). Similarly, humus has
very high CEC value compared to the inorganic clays (i.e., kaolinite). Thus, the
greater the CEC value, more is the exchange sites on soil minerals for organic and
inorganic species.
16 Causes, Effects and Sustainable Approaches to Remediate Contaminated Soil
461