Environmental Engineering Reference
In-Depth Information
for determining the interaction of trace elements with dis-
solved organic matter (van den Berg, 1984; Moffett and Zika,
1987; Sigleo and Means, 1990; Rue and Bruland, 1995; Wen
et al., 1996; Miller and Bruland, 1997; Wells et al., 1998).
The technique allows for the determination of the strength
of binding between the natural ligand(s) present and Hg
2
(i.e., determination of a conditional stability constant) and
also provides a measure of the abundance of the Hg binding
ligand concentration (L). Although this information is
highly useful for equilibrium modeling and bioavailability
predictions, it does not provide direct information on the
composition of the binding ligand(s).
Methods for determining the interaction of inorganic
Hg(II) species with DOM in natural waters and waste-
waters using the CLE approach have been described by
Hsu and Sedlak (2003), Han and Gill (2005), and Black
et al. (2007). Details about these analytical approaches
and results for determining the binding of inorganic
Hg(II) with natural organic matter are given in Table 3.5.
Methods to Assess Divalent Mercury-Organic
Matter Interactions
Several approaches to determine the interaction of
inorganic Hg(II) with dissolved organic matter in natu-
ral waters based on competitive ligand equilibrium (CLE)
approaches have been described. The technique is based on
an equilibrium competition between the natural ligands
present in the solution and an added ligand that has
well-characterized formation constants for free ionic Hg
2
.
table 3.5
Selected Summary of Analytical Approaches and Results for Determining the Binding of
Inorganic Divalent Mercury with Natural Organic Matter in Natural Waters
Matrix
Method
Log K
cond
(HgL
'
)
[L
'
]
a
Reference
Fresh and
saline water
Osteryoung square wave anodic
stripping voltammetry using a
gold disk electrode
9.7-10.8
1.4-4.5 nM
Wu et al. (1997)
Freshwater
Dual CLE using thiosalicylic acid
and diethyldithiocarbamate with
isolation and separation of
Hg-competing ligand complexes
by SPE on C18
29.9-33.5
0.022-11 nM
Black et al. (2007)
Coastal and
estuarine water
CLE using thiosalicylic acid and
chloride with solvent extraction
using toluene to isolate the
natural ligand Hg complex from
the competing ligand-Hg complex
26.5-29.0 (TSA)
23.1-24.4 (Cl)
0.013-0.10 nM
(using TSA);
0.5-9.6 nM
(using Cl)
Han and Gill (2005)
Lake, river, and
sea water
Isolation of an operationally
defi ned “reducible mercury”
fraction using stannous chloride
or sodium borohydride wet
chemical reduction combined
with ligand titrations
21-24
1-60 nM
Lamborg et al. (2003)
Wastewater
CLE using glutathione and with
isolation and separation of
Hg-competing ligand complexes
by SPE on C18
30
0.09-0.54 nM
Hsu and Sedlak (2003)
Hydrophobic
DOM isolates
Equilibrium dialysis and ligand
exchange using EDTA
22.5-23.5
b
5 nmol/mg
DOM
Haitzer et al. (2003)
DOM isolates
from the Florida
Everglades
CLE-SPE method involving the
titration of solutions containing
DOM and Hg with glutathione
25-31 (units
M
1
)
Gaspar et al. (2007)
CLE
competitive ligand exchange; SPE
solid-phase extraction; TSA
thiosalicylic acid.
a. [L
'
] represents the concentration of natural ligand not bound to Hg.
b. log K
cond
for the formation of Hg-DOM, units of L kg
1
.
