Air Quality Criteria for Lead Volume II of II - (NEPIS)(EPA) - US ...

Organic compounds in surface waters may originate from natural (e.g., humic or fulvic
acids) or anthropogenic sources (e.g., nitrilotriacetonitrile and ethylenediaminetetraacetic acid
[EDTA]) (U.S. Environmental Protection Agency, 1986b). The presence of organic complexes
has been shown to increase the rate of solution of Pb bound as Pb-sulfide (Lovering, 1976).
Soluble organic Pb compounds are present at pH values near 7 and may remain bound at pH
values as low as 3 (Lovering, 1976; Guy and Chakrabarti, 1976). At higher pH (7.4 to 9),
Pb-organic complexes are partially decomposed. Water hardness and pH were found to be
important in Pb-humic acid interactions (O’Shea and Mancy, 1978). An increase in pH
increased the concentration of exchangeable Pb complexes, while an increase in hardness tended
to decrease the humic acid-Pb interactions. Thus, the metals involved in water hardness
apparently inhibit the exchangeable interactions between metals and humic acids.
Marine Water
In marine systems, an increase in salinity increases complexing with chloride and
carbonate ions and reduces the amount of free Pb 2+ . In seawaters and estuaries at low pH, Pb is
primarily bound to chlorides (PbCl, PbCl2, PbCl3 !� , PbCl4 2! ) and may also form inorganic
Pb(HCO)3, Pb(SO4)2 2! , or PbCO3. Elevated pH in saltwater environments results in the
formation of Pb hydroxides (PbOH + , Pb(OH)2, Pb(OH)3 ! , Pb(OH)4 2! ) (Figure AX7-2.2.2).
A recent examination of Pb species in seawater as a function of chloride concentration suggested
that the primary species were PbCl3 ! > PbCO3 > PbCl2 > PbCl + > and Pb(OH) + (Fernando, 1995).
Lead in freshwater and seawater systems is highly complexed with carbonate ligands suggesting
that Pb is likely to be highly available for sorption to suspended materials (Long and Angino,
1977).
Current information suggests that inorganic Pb is the dominant form in seawater;
however, it has been shown that organically bound Pb complexes make up a large portion of the
total Pb (Capodaglio et al., 1990).
Sorption
Sorption processes (i.e., partitioning of dissolved Pb to suspended particulate matter or
sediments) appear to exert a dominant effect on the distribution of Pb in the environment
(U.S. Environmental Protection Agency, 1979). Sorption of Pb results in the enrichment of
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