conditions for both solubility and kinetic reasons. It is noteworthy that MTE
immobilization is not always a suitable treatment, as for example when top soils
are contaminated by radioelements or when stabilized in the form of strong
soluble complexes. Except for sulfide under anaerobic conditions and oxide
compounds, most of oxidized MTE are mobile. For example, in France their
regulated concentrations in water for discharge into the natural environment is
ranging from 0.1 to 5 mg l
À1 for the non-radioactive elements (Rodier et al.
2005). In conclusion, the most reactive oxidation states follow usually the order
M(I) > M (II) > M (IV), and so on, and the species that could be mobilized are
essentially mono and divalent MTEs (Wilkins 1991).
3. Metalloids (the most frequent are As, Sb, Se and Te) which have a rather low
volatility except for alkylated compounds of As and Se. Metalloids are dissolved
in water as oxyanions and are often present in soils as low solubility salts with
divalent or trivalent cations. They can be mobilized from soils by competing
anions such as phosphate or carbonate. Like for MTEs, their speciation often
depends on pH and redox potential. For example, As exists in the trivalent
(arsenite H 3 AsO 3 ) and pentavalent (arsenate H 3 AsO 4 ) oxidation states in GW
and form oxyanion complexes of different charges and properties upon pH; up to
height different forms are possible in pure water that behave differently in GW
(Watt and Le 2003). In addition, under anaerobic sulfidic conditions, As may be
found as soluble thioarsenic complexes. In contrast to arsenite and thioarsenic
forms, arsenate is easily removed from GW by precipitation. In France, the
regulated levels of metalloids for water discharged into the natural environment
are ranging from 0.1 to 5 mg l
À1 (Rodier et al. 2005).
4. Salts (the most usual are ClO x¼0–4
À , CN
À
, F
À , NO x¼2–3
À , SO 4
2À ) which are
inherently nonvolatile but very soluble in water. The management strategies are
either (bio)degradation by redox reactions or SL combined with on-site treatment
of leachates using degradation or concentration using reverse osmosis or adsorption (Nozawa-Inoue et al. 2005; Srinivasan and Viraraghavan 2009; Bardiya and
Bae 2011).
5. Hydrocarbons: they are distributed in several categories: light, heavy, saturated,
unsaturated among which aromatic (BTEX and PAHs), with heteroatoms (especially halogenated, oxygenated, nitrogen, sulfur and phosphorus compounds).
They are characterized by their octanol–water partition constant (K ow ) at room
temperature, in order to categorize them as hydrophilic (log K ow < 2) and
hydrophobic (log K ow > 4) (Schwarzenbach et al. 2003). Besides, the superficial
soil layers are often loaded with organic matter (OM). The soil organic carbon–
water partitioning coefficient (K oc ) of a compound is the ratio of its mass that is
adsorbed in the soil per unit mass of organic carbon in the soil per its equilibrium
concentration in solution. It is used to differentiate compounds that can be easily
adsorbed because of their hydrophobic character (log K oc > 4) from hydrophilic
ones (log K oc < 2). Most of the organic contaminants, mostly displaying hydrophobic features, have relatively low water solubility. Nevertheless, polar compounds and especially those able to generate H-bonds with water (e.g., alcohols,
amines, halogenated compounds) may have aqueous solubility much higher than
12
N. Fatin-Rouge
immobilization is not always a suitable treatment, as for example when top soils
are contaminated by radioelements or when stabilized in the form of strong
soluble complexes. Except for sulfide under anaerobic conditions and oxide
compounds, most of oxidized MTE are mobile. For example, in France their
regulated concentrations in water for discharge into the natural environment is
ranging from 0.1 to 5 mg l
À1 for the non-radioactive elements (Rodier et al.
2005). In conclusion, the most reactive oxidation states follow usually the order
M(I) > M (II) > M (IV), and so on, and the species that could be mobilized are
essentially mono and divalent MTEs (Wilkins 1991).
3. Metalloids (the most frequent are As, Sb, Se and Te) which have a rather low
volatility except for alkylated compounds of As and Se. Metalloids are dissolved
in water as oxyanions and are often present in soils as low solubility salts with
divalent or trivalent cations. They can be mobilized from soils by competing
anions such as phosphate or carbonate. Like for MTEs, their speciation often
depends on pH and redox potential. For example, As exists in the trivalent
(arsenite H 3 AsO 3 ) and pentavalent (arsenate H 3 AsO 4 ) oxidation states in GW
and form oxyanion complexes of different charges and properties upon pH; up to
height different forms are possible in pure water that behave differently in GW
(Watt and Le 2003). In addition, under anaerobic sulfidic conditions, As may be
found as soluble thioarsenic complexes. In contrast to arsenite and thioarsenic
forms, arsenate is easily removed from GW by precipitation. In France, the
regulated levels of metalloids for water discharged into the natural environment
are ranging from 0.1 to 5 mg l
À1 (Rodier et al. 2005).
4. Salts (the most usual are ClO x¼0–4
À , CN
À
, F
À , NO x¼2–3
À , SO 4
2À ) which are
inherently nonvolatile but very soluble in water. The management strategies are
either (bio)degradation by redox reactions or SL combined with on-site treatment
of leachates using degradation or concentration using reverse osmosis or adsorption (Nozawa-Inoue et al. 2005; Srinivasan and Viraraghavan 2009; Bardiya and
Bae 2011).
5. Hydrocarbons: they are distributed in several categories: light, heavy, saturated,
unsaturated among which aromatic (BTEX and PAHs), with heteroatoms (especially halogenated, oxygenated, nitrogen, sulfur and phosphorus compounds).
They are characterized by their octanol–water partition constant (K ow ) at room
temperature, in order to categorize them as hydrophilic (log K ow < 2) and
hydrophobic (log K ow > 4) (Schwarzenbach et al. 2003). Besides, the superficial
soil layers are often loaded with organic matter (OM). The soil organic carbon–
water partitioning coefficient (K oc ) of a compound is the ratio of its mass that is
adsorbed in the soil per unit mass of organic carbon in the soil per its equilibrium
concentration in solution. It is used to differentiate compounds that can be easily
adsorbed because of their hydrophobic character (log K oc > 4) from hydrophilic
ones (log K oc < 2). Most of the organic contaminants, mostly displaying hydrophobic features, have relatively low water solubility. Nevertheless, polar compounds and especially those able to generate H-bonds with water (e.g., alcohols,
amines, halogenated compounds) may have aqueous solubility much higher than
12
N. Fatin-Rouge