Biosurfactant Complexation of Metals and Applications for Remediation - Biosurfactants: Research Trends and Applications - page 280

s ourCes of m etals *
Trace element contamination occurs both naturally and as a result of anthropogenic
activities. The source and degree of contamination varies for atmospheric, aquatic,
and soil environments.
Atmospheric Environments
Natural sources of atmospheric trace elements include volcanic activity, forest fires,
wind-borne soil particles, seasalt spray, and biogenic, that is, biologically mediated
volatilization and biological particulates. The level of trace elements emitted from
each of these sources varies. Volcanic emanations account for 40%-50% of naturally
emitted As, Cr, Cu, Ni, Pb, and Sb annually. Atmospheric particulates derived from
soils can account for over 50% of Cr, Mn, and V. Seasalt spray and forest fires are
relatively minor contributors to natural trace-element emissions with less than 10%
of annual emissions for most elements. Biogenic contributions of metals in the atmo-
sphere can account for over 50% of Se, Hg, and Mo annually, and 30%-50% of As,
Cd, Cu, Mn, Pb, and Zn (Nriagu, 1989).
Anthropogenic atmospheric metal sources include fuel combustion (coal and
oil), metal production (mining and smelting), secondary metal production (nonfer-
rous and ferrous), refuse incineration, cement production, and wood combustion.
Like naturally occurring sources, the amount and types of metals emitted from each
source varies and depends on the source material for each process. For example, coal
combustion represents a major contributor of Hg, Mo, Sn, Se, As, Cr, Mn, Sb, and Tl,
while combustion of oil is a major contributor of V and Ni. Consumption of leaded
gasoline, primarily in developing countries, represents the largest contributor to Pb
emissions. Nonferrous metal production produces significant amounts of Pb, As, Cd,
Cu, In, and Zn emissions, while ferrous metal production is the primary source of
Cr and Mn (Nriagu and Pacyna, 1988; Pacyna and Pacyna, 2001). In 1990, anthro-
pogenic emissions into the atmosphere exceeded natural emissions by a factor of 28
for Pb, 6 for Cd, and 3 for V and Zn.
Aquatic Environments
Natural contributions of trace elements to aquatic environments are primarily from
settling of atmospheric particulates and fluvial movement of weathered material
into bodies of water. The trace elements introduced vary by source. The primary
anthropogenic sources of water contamination are domestic wastewater effluents
(As, Cr, Cu, Mn, and Ni); sewage discharges (As, Mn, and Pb); coal consumption
(As, Hg, and Se); ferrous and nonferrous metal production, that is, mining and smelt-
ing (Cd, Ni, Pb, Se, Cr, Mo, Sb, and Zn); and urban runoff (Nriagu, 1990; Nriagu
and Pacyna, 1988). Atmospheric fallout from sources listed in the previous section
is also a contributing factor. Anthropogenic metal inputs into aquatic environ-
ments are roughly twice those to the atmosphere (with the exception of Pb and Cd)
(Callender, 2003).
* Those interested in quantitative information regarding metal contamination should review Niagru
and Pacyna (1988) and Pacyna et al. (1995). From our literature review, it does not appear that there is
a more recent global inventory of metal emissions than that supplied by these authors.