Environmental Engineering Reference
In-Depth Information
et al. 1981 ; van Leeuwen et al. 2005 ). These complexes can undergo partitioning
between liquid-solid and solid-solid phases, thereby affecting the environmental
fate and transport of metals (Hays et al. 2004 ). (ix) The polyvalent cations and
their concentrations are considerably affected by the distribution of DOM frac-
tions and by their quantities (which can for instance be determined using XAD-8
resins), particularly at low DOC concentrations and high pH (Kaiser 1998 ). It
is also shown that hydrophilic DOC increases and hydrophobic DOC decreases
with increasing concentrations of metal cations, in the order Ca < Al < Fe, due
to formation of metal-DOM complexes (Kaiser 1998 ). (x) Complexation of
Fe 2 + by catechol and thiol ligands leads to the formation of aqueous species
that are capable of reducing substituted nitroaromatic compounds to the corre-
sponding anilines, and thus play an important role in the reductive transforma-
tion of persistent organic contaminants (Naka et al. 2006 ). (xi) Competition of
Cu(II), Co(II) and Ni(II) for the few (~1-10 % of the total) strong binding sites
of humic substances suggest that Ni(II) is bound to the much more numerous
(~99-90 % of the total) weak binding sites, forming labile nickel complexes.
The consequence is that Ni(II) is largely present as free nickel ion (Ni(II)-aquo
complex), which is reported to be toxic (Mandal et al. 1999 , 2000 ; Lavigne
et al. 1987 ). (xii) Metal binding properties of DOM and the interaction of
iron-DOM complexes with phosphate can decrease the concentration of dissolved
nutrients and subsequently act as nutrient reservoirs during periods of low
availability (Francko and Heath 1983 ; Jones 1998 ; Vahatalo et al. 2003 ). (xiii)
Complexes between As and humic acids are much stronger than As-protein or
As-fulvic acids ones. Therefore, intake of black soil (or dark brown soil) with
high amounts of humic acid could reduce As levels in the human body. Note that
while eating soil is quite unusual for humans, in some rural Bangladesh villages it
is customary for pregnant women to eat shikal (it sounds like “chain” in English),
which consists of small (2 in. × 1 in. × 1/2 in.) pellets made out of flooded soil
(information source is personal experience of one of the authors). While the origin
of this tradition is quite uncertain, it is noteworthy that it was observed in one of
the world's regions where human exposure to As is the highest.
8 Scope of the Future Research
It is reported that autochthonous fulvic acid of algal or phytoplankton origin,
typically shows fluorescence properties at peak C- and A-regions, which is a simi-
lar behavior as allochthonous fulvic and humic acids (Coble 1996 , 2007 ; Parlanti
et al. 2000 ; Mostofa and Sakugawa 2009 ; Zhang et al. 2009 ; Yamashita and Jaffe
2008 ; Stedmon et al. 2007 ; Mostofa et al. 2009b ; Fulton et al. 2004 ; Yamashita
and Tanoue 2004 ; Fu et al. 2010 ). Currently, PARAFAC modeling has been
applied to the identification of various fluorescent components and of their char-
acteristic changes (optical and chemical) when autochthonous fluorescent DOM
originates from algae or phytoplankton and undergoes photoinduced and microbial
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