Geoscience Reference
In-Depth Information
Table 15.5 Range of soil
solution concentrations for
certain trace elements;
estimates based on data
(Sauve and Parker 2005 )
Element
Soil solution lg/L
As
0.5-60,000
Cd
0.01-5,000
Cr
2-500
Cu
5-10,000
Ni
0.5-5,000
Pb
0.5-500
Se
1-100,000
Zn
1-100,000
(CH 3 -Hg-CH 3 ), which are volatile and absorbable by the organic fraction of the
subsurface solid phase or subsurface microorganisms.
The transformation of metal contaminants by complexation with inorganic or
organic ligands occurs mainly in the subsurface aqueous solution. The potential
inorganic ligands are nitrates, sulfate, chloride, and (bi)carbonate. Even though
their concentration is relatively high (i.e., millimolar), they are weak ligands with
minimal effect on metal contaminant complexation. Organic compounds, of bio-
logical origin present in the subsurface aqueous solution, comprise both weak and
strong metal-complexing ligands. Their composition is discussed in Chap. 1 . The
concentration of trace metals able to be complexed by organic ligands existing in
the subsurface aqueous solution may vary between uncontaminated and contam-
inated sites. Data indicating their range of concentration in soil solutions are
presented in Table 15.5 .
Speciation is a dynamic process that depends not only on the ligand-metal
concentration but also on the properties of the aqueous solution in chemical
equilibrium with the surrounding solid phase. As a consequence, the estimation of
aqueous speciation of contaminant metals should take into account the ion asso-
ciation, pH, redox status, formation-dissolution of the solid phase, adsorption, and
ion-exchange reactions. From the environmental point of view, a complexed metal
in the subsurface behaves differently than the original compound, in terms of its
solubility, retention, persistence, and transport. In general, a complexed metal is
more soluble in a water solution, less retained on the solid phase, and more easily
transported through the porous medium.
References
Alexander M (1977) Introduction to soil microbiology, 2nd edn. Wiley, New York
Alexander
M
(1980)
Biodegradation
of
chemicals
of
environmental
concern.
Science
211:132-138
Azadpour-Keeley A, Russell HH, Sewell GW (1999) Microbial processes affecting monitored
natural attenuation of contaminants in the subsurface. EPE/54o/S-99/001
Bode M, Stobe P, Thiede B, Schuphan I, Schmidt B (2003) Biotransformation of atrazine in
transgenic tobacco cell culture expressing human P450. Pest Manag Sci 60:49-58
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