health and safety plan solid waste management unit assessment

AUTOMOTIVE GASOLINE 65-17
gravitation
importance
and capillary forces
of some transformation
decreases evaporation,
pathways (see below),
reduces the
and may lead to
ground-water contamination.
65.2.2 Transformation Processes in Soil/Ground-water Systems
6.5.2.2.1 Chemical Transformation
No data were available on chemical transformation of gasoline in
the environment. However, as discussed in Chapter 64, photooxidation
has been reported to play a significant role in the chemical
degradation of some petroleum hydrocarbons in the sunlit environment
(1845,1848,2252,2259). Alkanes, benzenes, and mono-substituted
benzenes have been shown to be relatively resistant to photolysis in
aqueous systems: xylenes photolyxed slowly while trisubstituted
benxenes and naphthalenes photolyxed at rates competitive with
volatilization (1845). Penetration of oil below the soil surface
limits exposure to solar radiation while extensive lateral spreading of
oil over impermeable or rocky surfaces may promote substantial
photooxidative degradation. The oxygenated products of photooxidation
are generally more water-soluble .than the parent hydrocarbons and are
thus more likely to be leached from soil; enhanced toxicity of the
oxygenated hydrocarbons has also been observed (2248,2252).
65.2.2.2 Biological Degradation
Natural ecosystems have considerable exposure to petroleum
hydrocarbons from natural emissions, accidental contamination through
oil spills and storage tank leaks. and deliberate application to land
in disposal activities such as land-farming waste: therefore, their
biodegradation is of environmental importance. Numerous authors have
observed the biodegradation of petroleum hydrocarbons, and several
extensive reviews and reports are available (1846,2252,2255,2249,2253).
An extensive and diverse group of petroleum hydrocarbon-degrading
bacteria and fungi are widely distributed in the environment. The
reader is referred to Chapter 64 for a more detailed summary of the
biodegradation of petroleum hydrocarbons.
The.qualitative hydrocarbon content of petroleum mixtures largely
determines their degradability. In general, microorganisms exhibit
decreasing ability to degrade aliphatic hydrocarbons with increasing
chain length. n-Alkanes are considered more easily biodegraded than
branched or cyclic alkanes; aromatics are generally more rapidly
biodegraded than alkanes. The composition of gasoline suggests that
most of the aromatic species will be highly biodegradable, and many of
the aliphatic species that are not volatilized will be moderately
biodegradable. In a study of the biodegradation of individual
components of gasoline using microorganisms isolated from ground water,
the aliphatics and aromatics were shown to be sources of carbon for
Nocardb and pseudomow cultures, respectively (2331). Very few of
the remaining components supported bacterial growth: co-oxidation was
suggested as a possible mechanism for removal of non-growth components.
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