Environmental Engineering Reference
In-Depth Information
9
Metal
Con
taminationinUrbanWatersheds
9.1 Introduction
Metals naturally occur and are present in the soils, air, and water of all urban watersheds.
Although metal contamination is briefly mentioned in Chapter 7, we emphasize metals in
this chapter for a variety of reasons. First, metals are common and important contaminant
constituents in urban streams and stream sediment. Second, as noted in Chapter 7, metals
are commonly produced as by-products of many types of industrial, commercial, and even
residential developments. Third, metals are released into the environment. This is particu-
larly true in southeast Michigan, which developed as the focal point for the automotive
industry in the country and where metals are used as pigments in paints, as rust inhibi-
tors, metal plating, and in raw materials. Fourth, metals are interesting to study because
they are subject to a number of reactions in soil and sediment including sorption and
precipitation and are greatly influenced by the redox conditions in these environments.
Fifth, metals can be used to inexpensively screen for contamination at old industrial sites
(brownfields), without knowing the site history. For example, the USEPA lists 14 metals
(Sb, As, Ba, Be, Cd, Cr, Cu, Pb, Hg, Ni, Se, Ag, Th, and Zn) as part of their 129 most com-
mon pollutants (USEPA 2003). These metals can all be analyzed simultaneously and inex-
pensively using ICP-MS (inductively coupled plasma mass spectrometry), as opposed to
the higher cost and longer time required to randomly test for the presence of hundreds of
organic compounds at an undocumented brownfield site.
Historically, soil scientists and geologists have studied near-surface soil for agricultural
or farming purposes to better understand natural ecosystems (Thornton 1991) or to focus
on the health effects in urban areas associated with one or two metals (Mielke et al. 1983).
As a result, there has been little information available on the background level of metals in
the near-surface soil in urban areas.
In this chapter, we focus on anthropogenic activities related to 100 years of industrializa-
tion in the metropolitan Detroit area and explore how this history has contributed to the
contamination of the soil, stream sediment, and groundwater by many of the 14 metals
listed above. Two case studies are presented: the first addresses heavy metal contamina-
tion in soil and evaluates the background and anthropogenic levels of metals and the
second focuses on dissolved metals in groundwater.
9.2 Heavy Metals in Soil
Metals naturally occur in soil in one or more of seven different ways: (1) dissolved in
soil solution, (2) occupying exchange sites on inorganic constituents, (3) adsorbed in inor-
ganic constituents, (4) associated with insoluble soil organic matter, (5) precipitated as pure
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