Environmental Engineering Reference
In-Depth Information
except for the dissolved gases nitrogen, oxygen, argon, hydrogen, and so on. In some
cases colloidal-size carbon particles may be present and may be of particular concern
because of their high sorptive capacity [5].
The solid phase of soil, regolith, and rock will contain very small amounts of noble
metals in the elemental state [6]. There will be some elemental carbon present, much of it
as a result of fire, either natural or man-made [5]. There may also be some gaseous
elements trapped in solid matrices in soil. The overwhelming amounts of the inorganic
components are in the form of ions and molecules.
In some places the soil, regolith, and rock may contain arsenic and uranium. Radon
when found comes from the decomposition of uranium in the regolith. It is of note
because of its diffusion into house basements [7- 10].
9.2.1. Elements in Combination
Many more elements than those mentioned above are commonly found in the
environment but are present as compounds or ions rather than in the elemental state.
Of the 110 or so elements in the periodic table, 36—or 33%—are common and
important in the lithosphere. Their importance comes either because they are essential for
plants or are needed in the diets of animals, or because they or one of their forms is toxic.
In addition there are other elements, such as silver, gold, argon, and helium, found in low
concentrations, that are not essential to plants or animals and are not toxic. Because of
their environmental and economic importance all have had specific analytical procedures
developed for their detection and measurement.
In Table 9.1 the elements commonly analyzed for are arranged in three columns. The
first column shows elements essential to plants and animals. The second shows elements
toxic to plants and animals at high concentrations but essential at low concentrations. The
third contains elements generally considered to be toxic. Not all elements listed in
column 1 are essential for all plants and animals. For instance, cobalt (Co) is generally
not needed by plants, but is essential in the nutrition of animals. Likewise, silicon is not
essential to animals, but is for some plants. The same thing can be said in column 2. As
shown in column 3, some elements, such as aluminum (A1), are toxic to plants but not to
animals. On the other hand, lead (Pb) is toxic to humans but is not especially toxic to
plants [11]. The last
TABLE 9.1 Elements Found in Soil
Plant and animal essential
elements found as ions
Essential and
toxic
Potentially
toxic
Found in elemental
form
Macro a
H 2
Se
Al
O 2
H
B
Li
N 2
C
As
Ba
O
Na
Rb
Rn
 
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