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

Figure AX7-2.2.2. Lead speciation versus chloride content (Fernando, 1995).
bed sediments, particularly in environments with elevated organic matter content from
anthropogenic sources. Lead adsorption to aquatic sediments is correlated with pollution in sites
containing high levels of anthropogenic organic content, even under acidic conditions (Tada and
Suzuki, 1982; Brook and Moore, 1988; Davis and Galloway, 1993; Botelho et al., 1994; Davis
et al., 1996). Particulate-bound forms are more often linked to urban runoff and mining effluents
(Eisler, 2000).
Solid Pb complexes form when Pb precipitates or adsorbs to suspended particulate matter
and sediments. Inorganic Pb adsorption to suspended organic matter or sediments is dependent
on parameters such as, pH, salinity, water hardness, and the composition of the organic matter
(U.S. Environmental Protection Agency, 1979). In addition to suspended organic matter, Pb can
adsorb to biofilms (i.e., bacteria) (Nelson et al., 1995; Wilson et al., 2001). Adsorption typically
increases with increasing pH, increasing amounts of iron or manganese; and with a higher degree
of polarity of the particulate matter (e.g., clays). Adsorption decreases with water hardness
(Syracuse Research Corporation, 1999). At higher pH, Pb precipitates as Pb(OH) + and PbHCO3 +
into bed sediments (Weber, 1993). Conversely, at low pH, Pb is negatively sorbed (repelled
from the adsorbent surface) (U.S. Environmental Protection Agency, 1979; Gao et al., 2003).
In addition, Pb may be remobilized from sediment with a decrease in metal concentration in the
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