Geoscience Reference
In-Depth Information
Fig. 17.13 Distribution of
Pu and Am in saline
groundwater, as affected by
the presence of humic and
fulvic acids (Japan Atomic
Energy Research Institute
2000
)
adsorption-desorption study suggested that the rates of Cd retention and release
differ
not
only
between
bacterial
species
but
also
between
unattached
and
deposited bacteria (Pang and Simunek
2006
).
When heavy metals reach groundwater, they may become bioavailable and thus
toxic to some organisms and/or for groundwater used as drinking water. It should
be stressed that once released to the soil-subsurface environment, heavy metals
cannot be degraded. The only processes that may affect them are transport,
immobilization, and changes in their oxidation state. Heavy metals adsorb onto the
mineral fraction of the solid phase and suspended particles in the liquid phase, and
become a continuous source of groundwater contamination due to their slow rate
of desorption. Therefore, metal contaminants become, essentially, permanent
microcomponents of the porous medium and groundwater, which consequently
leads to irreversible changes in groundwater composition.
