McKay, Donald. "Front matter" Multimedia Environmental Models ...

of complex and variable structure that are naturally present in soils, water, and
sediments. They are the remnants of living organic materials, such as wood, that
has been subjected to prolonged microbial conversion. These acids are sparingly
soluble in water, but the solubility can be increased at high pH.
The esters or “salts” or organic acids and alcohols tend to be relatively innocuous
and short-lived in most cases. A notable exception is the phthalate esters, which are
very stable oily substances and are invaluable additives (plasticizers) for plastics,
rendering them more flexible. Notable among the phthalate esters is diethylhexylphthalate
(DEHP), the ester with two molecules of 2 ethylhexanol. The other esters
of interest are the glycerides—for example, glyceryl trioleate, the ester of glycerine
and oleic acid. This chemical has similar properties to fat and has been suggested
as a convenient surrogate for measuring fat to water partitioning.
The “dioxins” and “furans” are two series of organic compounds that have
become environmentally notorious. The chlorinated dibenzo-p-dioxins were never
produced intentionally but are formed under combustion conditions when chlorine
is present. They form a series of very toxic chemicals, the most celebrated of which
is 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD). TCDD is possibly the most toxic
chemical to mammals. A dose of 2 mg of TCDD per kg of body weight is sufficient
to kill small rodents.
A related series of chemicals is the dibenzofurans, which are similar in properties
to the dioxins. It appears that molecules that are long and flat, with chlorine atoms
strategically located at the ends, are particularly toxic. Examples are the chloronaphthalenes,
DDT, the PCBs, and chlorinated dibenzo-p-dioxins and dibenzofurans.
Other oxygenated compounds of interest include carbohydrates, cellulose, and
lignins, which occur naturally.
3.3.2.4 Nitrogen Compounds
Nitrogen compounds of environmental interest include amines, amides,
pyridines, quinolines, and amino acids, and various nitro compounds including nitro
polycyclicaromatics and nitroso compounds. Many of these compounds occur naturally,
are quite toxic, and are difficult to analyze.
3.3.2.5 Sulfur Compounds
Sulfur compounds, including thiols, thiophenes, and mercaptans, are well known
because of their strong odor. One of the most prevalent classes of synthetic organic
chemicals is the alkyl benzene sulfonates, which are widely used in detergents.
3.3.2.6 Phosphorus Compounds
Phosphorus compounds play a key role in energy transfer in organisms. Organophosphate
compounds have been developed as pesticides (e.g., chloropyrifos), which
have the very desirable properties of high biological activity but relatively short
environmental persistence. They have therefore largely replaced organo-chlorine
compounds in agriculture.
©2001 CRC Press LLC