Environmental Engineering Reference
In-Depth Information
organic material (carbon containing) and concentrations of specific organic
molecules are also of interest. The chemistry of natural waters is an entire
field of study (Stumm and Morgan, 1981; Brezonik, 1994).
Chemical materials in aquatic systems can either be
dissolved
or
par-
ticulate
. The distinction between dissolved materials and particulate mate-
rials is arbitrary and generally is based on their ability to pass through a
filter of a specified size. For example, dissolved metals and dissolved or-
ganic carbon are defined as those which pass through a 0.45-
m filter, but
total dissolved solids are determined using material that passes through a
filter with slightly greater than 1
m retention (Eaton
et al.,
1995). Re-
cently, a more natural definition scheme has been proposed (Gustafsson
and Gschwend, 1997) in which chemicals are divided into three classes:
dissolved,
colloidal
(particles not settled by gravity), and
gravitoidal
(par-
ticles that will settle) (Fig. 11.2). The colloid is defined specifically as any
particle whose movement is not affected significantly by gravitational set-
tling and that provides a location where chemicals can escape from the
aqueous solution.
FIGURE 11.2
Chemical associations with dissolved, colloidal, and gravitoidal particles. The
association is depicted with three trace substances, inorganic copper and magnesium ions and
the three-ringed organic compound phenanthrene. Dissolved chemicals depicted include a va-
riety of organic chemicals. Colloidal particles include membrane pieces, viruses, inorganic pre-
cipitates, and aggregation of organic chemicals. Gravitoidal particles include clays, planktonic
cells, and larger aggregates of organic and inorganic materials (redrawn from Gustafsson and
Gschwend, 1997).
Search WWH ::
Custom Search