797
Complexation of Dissolved Organic Matter with Trace Metal Ions in Natural Waters
The conditional stability constants for the complexation of hydrophobic or hydrophilic fractions of DOM or autochthonous DOM with metal ions are 7.8–9.6 (log 10
K 1 ) for Zn 2+ -DOM; 8.92–16.3 (log 10 K 1 ) and 6.87–12.9 (log 10 K 2 ) for Cu 2+ -DOM;
11.6–31.0 (log 10 K 1 ) and 10.5–11.2 (log 10 K 2 ) for Hg 2+ -DOM in lakes, estuaries and
oceans (Table 1) (Haitzer et al. 2002; Xue and Sigg 1993; Xue et al. 1995; van Den
Berg et al. 1987; Sunda and Huntsman 1991; Sunda and Hanson 1987; Sunda and
Ferguson 1983; Moffett et al. 1990; Coale and Bruland 1988, 1990; van Den Berg
1984; Midorikawa and Tanoue 1996; Benoit et al. 2001; Drexel et al. 2002; Gasper
et al. 2007; Hsu and Sedlak 2003; Sander et al. 2005; Shank et al. 2006). It has been
shown that the conditional stability constants between autochthonous DOM of phytoplankton or algal origin and Cu 2+ are much higher (log 10 K 1 = 13.9–15.6 and log 10
K 2 = 11.8–13.4) in lakes, and they are similar to those of organic ligands of phytoplankton or biological sources (11.1–13.2 and 9.2–10.2, respectively) in estuaries
and seawater compared to those of allochthonous fulvic and humic acids (Table 1)
(Xue and Sigg 1993; Xue et al. 1995; van Den Berg et al. 1987; Moffett et al. 1990;
Coale and Bruland 1988; Coale and Bruland 1990; Sunda 1988). Surface water from
the Irish Sea and the Atlantic Ocean contains ligand concentrations of 1.7 × 10 −7
and 1.1 × 10 −7 M, with conditional stability constants (log 10 K) of 9.84 ± 0.13 and
9.86 ± 0.23, respectively, at pH 8.0 (van Den Berg 1982).
The conditional stability constants of the Hg 2+ -DOM complexation are
significantly higher for the hydrophobic fraction of DOM or DOM in natural
surface waters (Table 1) (Haitzer et al. 2002, 2003; Benoit et al. 2001; Drexel et al.
2002; Gasper et al. 2007; Hsu and Sedlak 2003; Ravichandran et al. 1998; 1999;
Lamborg et al. 2003, 2004; Waples et al. 2005). The high affinity of the Hg 2+ -
DOM complexation is responsible for the reduced S-containing binding sites (thiol
and disulfide/disulfane functional groups) bound in DOM, presumably autochthonously produced in natural waters (Haitzer et al. 2002; Benoit et al. 2001; Gasper
et al. 2007; Dyrssen and Wedborg 1986; Schuster 1991; Guentzel et al. 1996;
Wallschlager et al. 1996; Xia et al. 1999). The possible complexation reaction
can be written as [Hg 2+ + R-SH n− = HgR-S (n−1)− + H + ] (Benoit et al. 2001;
Dyrssen and Wedborg 1991).
The conditional stability constants for the complexation of the two major binding
sites of tryptophan with metal ions are 4.88–4.90 (log 10 K 1 ) for Cu 2+ -tryptophan;
7.82–9.56 for Cu 2+ -tryptophan; and 4.99–5.33 for Hg 2+ -tryptophan for peak T at
Ex/Em = 275–285/330–360 nm in aqueous solution (Table 1) (Fu et al. 2007; Hays
et al. 2004; Wu and Tanoue 2001b).
The conditional stability constants (log 10 K 1 and log 10 K 2 ) for the complexation of two major binding sites of EPS with metal ions are 3.98–4.12 (log 10
K 1 ) and 4.28–4.48 (log 10 K 2 ) for Hg 2+ -EPS; 0.45–4.9 (log 10 K 1 ) and 3.2–4.6
(log 10 K 2 ) for Pb 2+ -EPS; 1.54–3.5 (log 10 K 1 ) and 2.7–3.8 (log 10 K 2 ) for Cd 2+ -
EPS; 3.0–4.4 (log 10 K 1 ) for Cu 2+ -EPS; and 2.6–3.0 (log 10 K 1 ) for Ni 2+ -EPS
in aqueous solution (Table 1) (Zhang et al. 2010; Guibaud et al. 2004, 2006;
Comte et al. 2006). The conditional stability constants of Hg 2+ -EPS complexes are relatively low (3.98–4.12: log 10 K 1 ) at peak T (Ex/Em = 275–
280/328–334 nm) compared to those (4.28–4.48: log 10 K 2 ) at peak T UV (Ex/
Complexation of Dissolved Organic Matter with Trace Metal Ions in Natural Waters
The conditional stability constants for the complexation of hydrophobic or hydrophilic fractions of DOM or autochthonous DOM with metal ions are 7.8–9.6 (log 10
K 1 ) for Zn 2+ -DOM; 8.92–16.3 (log 10 K 1 ) and 6.87–12.9 (log 10 K 2 ) for Cu 2+ -DOM;
11.6–31.0 (log 10 K 1 ) and 10.5–11.2 (log 10 K 2 ) for Hg 2+ -DOM in lakes, estuaries and
oceans (Table 1) (Haitzer et al. 2002; Xue and Sigg 1993; Xue et al. 1995; van Den
Berg et al. 1987; Sunda and Huntsman 1991; Sunda and Hanson 1987; Sunda and
Ferguson 1983; Moffett et al. 1990; Coale and Bruland 1988, 1990; van Den Berg
1984; Midorikawa and Tanoue 1996; Benoit et al. 2001; Drexel et al. 2002; Gasper
et al. 2007; Hsu and Sedlak 2003; Sander et al. 2005; Shank et al. 2006). It has been
shown that the conditional stability constants between autochthonous DOM of phytoplankton or algal origin and Cu 2+ are much higher (log 10 K 1 = 13.9–15.6 and log 10
K 2 = 11.8–13.4) in lakes, and they are similar to those of organic ligands of phytoplankton or biological sources (11.1–13.2 and 9.2–10.2, respectively) in estuaries
and seawater compared to those of allochthonous fulvic and humic acids (Table 1)
(Xue and Sigg 1993; Xue et al. 1995; van Den Berg et al. 1987; Moffett et al. 1990;
Coale and Bruland 1988; Coale and Bruland 1990; Sunda 1988). Surface water from
the Irish Sea and the Atlantic Ocean contains ligand concentrations of 1.7 × 10 −7
and 1.1 × 10 −7 M, with conditional stability constants (log 10 K) of 9.84 ± 0.13 and
9.86 ± 0.23, respectively, at pH 8.0 (van Den Berg 1982).
The conditional stability constants of the Hg 2+ -DOM complexation are
significantly higher for the hydrophobic fraction of DOM or DOM in natural
surface waters (Table 1) (Haitzer et al. 2002, 2003; Benoit et al. 2001; Drexel et al.
2002; Gasper et al. 2007; Hsu and Sedlak 2003; Ravichandran et al. 1998; 1999;
Lamborg et al. 2003, 2004; Waples et al. 2005). The high affinity of the Hg 2+ -
DOM complexation is responsible for the reduced S-containing binding sites (thiol
and disulfide/disulfane functional groups) bound in DOM, presumably autochthonously produced in natural waters (Haitzer et al. 2002; Benoit et al. 2001; Gasper
et al. 2007; Dyrssen and Wedborg 1986; Schuster 1991; Guentzel et al. 1996;
Wallschlager et al. 1996; Xia et al. 1999). The possible complexation reaction
can be written as [Hg 2+ + R-SH n− = HgR-S (n−1)− + H + ] (Benoit et al. 2001;
Dyrssen and Wedborg 1991).
The conditional stability constants for the complexation of the two major binding
sites of tryptophan with metal ions are 4.88–4.90 (log 10 K 1 ) for Cu 2+ -tryptophan;
7.82–9.56 for Cu 2+ -tryptophan; and 4.99–5.33 for Hg 2+ -tryptophan for peak T at
Ex/Em = 275–285/330–360 nm in aqueous solution (Table 1) (Fu et al. 2007; Hays
et al. 2004; Wu and Tanoue 2001b).
The conditional stability constants (log 10 K 1 and log 10 K 2 ) for the complexation of two major binding sites of EPS with metal ions are 3.98–4.12 (log 10
K 1 ) and 4.28–4.48 (log 10 K 2 ) for Hg 2+ -EPS; 0.45–4.9 (log 10 K 1 ) and 3.2–4.6
(log 10 K 2 ) for Pb 2+ -EPS; 1.54–3.5 (log 10 K 1 ) and 2.7–3.8 (log 10 K 2 ) for Cd 2+ -
EPS; 3.0–4.4 (log 10 K 1 ) for Cu 2+ -EPS; and 2.6–3.0 (log 10 K 1 ) for Ni 2+ -EPS
in aqueous solution (Table 1) (Zhang et al. 2010; Guibaud et al. 2004, 2006;
Comte et al. 2006). The conditional stability constants of Hg 2+ -EPS complexes are relatively low (3.98–4.12: log 10 K 1 ) at peak T (Ex/Em = 275–
280/328–334 nm) compared to those (4.28–4.48: log 10 K 2 ) at peak T UV (Ex/