Introduction to Soil Chemistry

ioorganic 57
activity may be increased, decreased, unchanged, or completely destroyed
[15,16].
All biomolecules tend to be large polymer or polymerlike combinations of
individual molecular units that can be isolated by either acidic or basic hydrolysis.
Lipids and fats are found as integral parts of membranes and cell walls.
Polysaccharides are used as structural units and as stored energy sources. Proteins
are used to construct muscle and enzymes that also contain metals such
as zinc, manganese, and iron. There are many other important biomolecules
present at lower concentrations, such as DNA and RNA, which are also
released into the soil solution. All can be the source of smaller molecules in
the soil solution.
The different groups of biomolecules, lipids, polysaccharides, and proteins,
illustrated in Figure 3.9, decompose at different rates depending on their composition.
Lipids and fats are slower to decompose in soil because of their insolubility
in water. Large polysaccharides are also insoluble in water but are more
quickly decomposed than are fats. Proteins and compounds such as DNA and
RNA are more quickly decomposed in part because they contain nitrogen
(fixed), which is often in short supply in the environment.
Biochemicals will be present in soil during any analysis and can react with
components of interest, either organic or inorganic, including sand, silt, and
clay particles. Possible reactions include chelation, decomposition, precipitation,
solubilization, or dissolving such as dissolving in soil organic matter
(humus). Several of these reactions will take place simultaneously and can lead
to nondetection of the component of interest or an analytical result that is
much lower than the true value [15].
3.5. BIOORGANIC
Bioorganic components in soil include those organic molecules that participate
in biochemical reactions; are responsible for the initiation of a reaction,
eliciting the formation of a compound or an antibiotic; or are inhibitors. Bioorganic
chemistry also uses synthesized models and molecules, to study biological
processes such as enzymatic activity. Often these studies are
undertaken to develop a mechanism for the reactions of interest. Bioorganic
molecules will be present either as components of the synthesis chain or as
part of the degradation products. Whenever cells lyse, these compounds will
be released into the soil solution. Their moderate size and complexity will
allow them to be metabolized rapidly.
Because of their moderate size and complexity, bioorganic molecules can be
confused with analytes of interest. They can have the same or similar retentions
times, during chromatographic procedures, as the analytes of interest and
thus can indicate the presence of more molecules than are actually the case or
even the presence of an analyte or contaminant when it is not or has not been
added from an external source. It is also possible for gas chromatographic/mass