Selected Research Findings: Contaminant Transport - Contaminant Geochemistry - page 280

Chapter 12
Selected Research Findings: Contaminant
Transport
Many factors affect the transport of contaminants in the subsurface, including the
(spatially and temporally variable) hydraulic and physicochemical characteristics
of the solid phase and the properties of water and the contaminants themselves. In
this chapter, we focus on several specific groups of contaminants, including heavy
metals and metalloids, nanomaterials, pesticides, and petroleum hydrocarbons, as
representative examples of reactive (nonconservative) contaminant transport.
12.1 Heavy Metals and Metalloids
During their transport in soil and subsurface environments, heavy metals and
metalloids (recall Sect. 3.5 ) may be involved in a series of surface-induced,
chemical, and biological reactions. Solid-phase properties, water-phase composi-
tion, and microorganisms presence control the retention and mobility of heavy
metals and metalloids, and their complexation, during transport through the soil
and subsurface. Important factors affecting heavy metal and metalloid mobility in
the soil-subsurface system are the pH of the ambient solution, sorbent nature, and
presence and concentration of organic and inorganic ligands, including humic and
fulvic acids, and root exudates. Chemical and biochemical processes involved in
heavy metal and metalloid mobility in soil-subsurface systems are sorp-
tion-desorption, oxidation-reduction, complexation-dissociation, and precipita-
tion-dissolution. Preferential flow of water into the soil-subsurface system induces
an increase in heavy metal and metalloid transport, either as solute or adsorbed on
colloidal materials. For an extended presentation of this topic, the reader is
directed to the reviews of Kretzschmar et al. ( 1999 ), Violante et al. ( 2010 ) and
Selim ( 2013 ).