Environmental Engineering Reference
In-Depth Information
from soils that have row crops or soils which are sparsely vegetated.
Microorganisms can also change soil's physical and chemical characteristics. Through
the production of microbial gums, sand, silt, and clay particles can be cemented together
and change infiltration and percolation through soil. More important, microorganisms can
dramatically change the chemical characteristics of soil. Rapid decomposition of organic
matter can deplete soil air of oxygen, creating anaerobic conditions. Microorganisms can
also change the oxidation state of inorganic ions around them. In this way
microorganisms can dramatically change the components present and therefore the
components one is looking for may be dramatically changed. Final and intermediate
decomposition products may be present in the same sample.
Because of these differences sampling will be different for different environments.
Typically sod can be sampled on a random basis. Pastures with animals will be a little
different because of animal tracks and manure, both of which should be avoided when
sampling. In tree-covered areas there may or may not be vegetation between the trees. In
any case sampling must be done between trees as randomly as possible. In industrial
areas the same concepts must be observed; that is, plants may accumulate contaminants.
Animal holes and other soil cracks will allow components to move rapidly into and
through soil; thus all these potential sampling considerations need to be kept in mind.
In addition to animals being present their activity is also important. Any environmental
condition that changes the activity of animals may also change the occurrence of the
compounds associated with them. Unusually wet, dry, hot, or cool conditions and the
seasons will change animal and plant activity, thus weather conditions and the date can
change the types of compounds found, and this should be noted in the project notebook
and taken into consideration when interpreting analytical results [26].
9.6.
CONCLUSIONS
Soil contains a large and diverse number of inorganic, organic, and biological molecules.
The inorganic component comes from the breakdown and leaching of rock and minerals.
The organic components come from organic matter added to the soil by plants, animals,
and microorganisms. This same group provides biochemical molecules, enzymes,
proteins, fats, carbohydrates, nucleic acids, and lignins to the soil. In addition, the
breakdown of animal and plant tissue releases intracellular constituents to the
environment, particularly the soil solution. Because of the intimate relationship between
soil and water, these compounds may be found in water. Any of these compounds that are
gaseous can also be found in the atmosphere. In addition to chemical change plants,
animals and micro-organisms can create physical changes in soil that affect sampling.
It would simplify things greatly if all the reactions taking place in soil could be
elucidated and described fully. There are always new and often unexpected reactions
being discovered, however. For instance, microorganisms can carry out both
transhalogenation and chlorine bromine exchange in halomethane. This complicates both
the quantification and the understanding of the source and fate of these compounds in the
environment [27].
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