Geoscience Reference
In-Depth Information
Table 4.10
The abundance of various
elements (in ppm) in igneous rocks,
soils, fresh water, land plants and land
animals (from Bowen 1966).
Element
Igneous rock
Soils
Fresh water
Land plants
Land animals
Ag
0.07
0.1
0.00015
0.06
0.006
Al
80,000
70,000
0.25
500
4-100
As
1.8
6
0.004
0.2
≤
0.2
Cd
0.2
0.06
<
0.08
0.6
≤
0.5
Co
25
8
0.0009
0.5
0.03
Cr
100
100
0.0002
0.25
0.075
Cu
50
20
0.01
15
2.5
Fe
55,000
40,000
0.65
140
160
Hg
0.08
0.03-0.8
0.00008
0.015
0.045
Mn
1000
900
0.01
650
0.2
Mo
1.5
2
0.00035
0.9
<
0.2
Ni
75
40
0.01
3
0.8
Pb
15
10
0.005
2.5
2
Sn
2
10
0.00004
<
0.3
<
0.15
V
150
100
0.001
1.5
0.15
Zn
70
50
0.01
100
150
Surfaces of fine-grained particles are chemic-
ally active. Surface sites are positively or nega-
tively electrically charged or neutral. Adsorption
reactions between charged surfaces and pollut-
ants in ionic form include different types of
physical/chemical bindings. Pollutants may occur
as free uncomplexed species or as various com-
plexes. Pollutants are attracted to different types
of carrier particles depending on their inherent
chemical properties. Fine-grained carrier particles
have a large surface area per weight unit and are,
thus, important for the migration of pollutants.
Carrier particles exist in a wide size spectrum.
From 1 nm size (10
−9
m) up to approximately
0.45
(Eh). These factors influence the pollutants in
a number of ways. The formation of import-
ant carrier particles, for example iron (Fe) and
manganese (Mn) precipitates, are, for example,
enhanced by high pH and Eh. The presence of
O
2
determines the presence of oxides, such as
Fe-oxides, or reduced species, which is import-
ant for pollutant cycling in lakes. The survival
of higher life forms, such as zoobenthos, also
depends on the supply of oxygen. The pH value
has a major influence on many chemical/physical
processes, some of which are important for the
migration of pollutants. The H
+
ions compete
for carrier particle binding sites with pollutants.
A lower pH generally decreases the
K
d
value.
Flocculation of carrier particles also depends
on pH. With increased pH the usually negative
charges of natural particles increase and the
particles become less likely to flocculate.
The distribution form of the metal in aquatic
environments is very important for the toxicity
and the potential ecosystem effects (Gottofrey
1990; Wicklund 1990). Generally, the toxicity
is highest for the ionic species and propor-
tional to the oxidation number, for example
CrO
−
is more toxic than Cr
3+
. The potential
toxic effects of metals can often be signific-
antly reduced because the metals are bound to
different compounds, which may camouflage
the toxic properties. Low pH and high redox
m (10
−6
m) the particles are generally
called colloids. From 0.45
μ
m to about 0.15 mm,
particles suspended in water settle according to
Stokes' law by laminar flow (cohesive material).
It should also be noted that suspended particles are
constantly moving and they aggregate (flocculate)
and disaggregate as a result of collisions and reac-
tions with other particles and fluid shear. The
carrier particles may be classified into organic
(e.g. humic matter) and inorganic (e.g. clays,
(hydr-)oxides, Fe/Mn precipitates) or according
to genetic origin (e.g. biogenic (mainly organic)
or pedogenic (mainly inorganic matter)).
The chemical environment can be expressed
in terms of, for example, pH (i.e. the availabil-
ity of H
+
ions), oxygen (O
2
) and redox potential
μ
