110
Trace Elements in Abiotic and Biotic Environments
15.2 SOILS
The average F contents in soils have been estimated to be 329 and 360  mg/kg,
for European and the U.S. soils, respectively, but within the broad range of
<1–1360 mg/kg (Table 15.1). Its highest concentrations are in heavy loamy soils
and the lowest in organic soils. Its F content in soils is inherited form the parent
material, but its distributions reflect soil-forming processes and soil texture. Soils
may accumulate relatively high amounts of F, especially in B horizons, usually
enriched in the amorphous Al hydroxides. Soils derived from bedrocks enriched
in F usually contain its increased level (>1000 mg/kg), and are of a great environmental problem because they are associated with the endemic provinces of fluorosis (Ermakov 2004; Chen et al. 2008).
The behavior of F in soils is variable and highly controlled by pH, clay contents,
concentrations of Ca and P, and Al hydroxides. The most common F compound
in soils is fluoroapatite, but other fluorides are also present. Its mobile species are
NaF, KF, and NH 4 F, whereas AlF 3 , CaF 2 , and MgF 2 are very slightly mobile. In
soil solutions, both cationic (AlF 2+ , AlF + ) and anionic F species (F – , AlF 4
– , AlF 6
3– ,
SiF 6
2– ) occur. In certain soils, in which CaF 2 and mobile Al species are present, F is
fixed and in a relatively insoluble aluminum fluorosilicate, Al 2 (SiF 6 ) 3 , form. In calcareous soils, F is very slightly mobile, whereas in sodic and some acidic soils, it is
TABLE 15.1
Fluorine Contents in Soils, Water, and Air
Environmental Compartment
Range
Soil (mg/kg)
Light sandy
80–205
Medium loamy
175–462
Heavy loamy
470–1360
Calcerous (calcisols)
470–680
Organic (histosols)
<1–350
Water (μg/L)
Rain
50
River
50–2700
Sea, ocean
30–1350
Air (ng/m 3 )
Industrial and urban regions
1–7
Source: Data are given for uncontaminated environments,
from Kabata-Pendias, A and Mukherjee, A.B.,
Trace Elements from Soil to Human, Springer,
Berlin, Germany, 2007; Reimann, C. and de
Caritat, P., Chemical Elements in the Environment,
Springer-Verlag, Berlin, Germany, 1998.