Environmental Geosciences

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Environmental Geosciences

• Human Interactions with the Environment

Organics
Andrea Koschinsky
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Distribution and Transformation of Organic
Compounds
Basic principles of pollutant distribution and
transformations. The factors controlling
chemodynamics include Henrys constant,
sorption/distribution coefficients,
bioconcentration factor, and KOW.
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Distribution and Transformation of Organic
Compounds
Materials properties and environmental behavior
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Transport and Sorption of Organic Compounds
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Transport and Cycling of Organic Compounds
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Transport and Cycling of Organic Compounds
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Transport and Cycling of Organic Compounds
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Transport and Sorption of Organic Compounds
KOA octanol-air partitioning coefficient PL
vapor pressure of the subcooled liquid TC
condensation temperature
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Transport and Sorption of Organic Compounds
CFCs Chlorofluorocarbons PCDD polychlorinated
dibenzo-p-dioxin, PCDF polychlorinated
dibenzofuran
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Transport and Cycling of Organic Compounds
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Transport and Cycling of Organic Compounds
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Degradation of Organic Compounds
Transformation processes of organic matter
Abiotic and biotic processes Chemical and
biological transformation processes control the
ultimate fate of hydrocarbons released into the
environment. The transformation reactions differ
depending on the environmental compartment within
which the compounds reside and vary with chemical
structure. When hydrocarbons are released to the
atmosphere or surface waters, photochemical
oxidation, an abiotic process, can occur. In
soils and groundwater and surface waters,
biologically mediated degradation of hydrocarbons
is the most important transformation process. In
the absence of light, chemical degradation
reactions at Earth surface temperature and
pressure are relatively unimportant compared to
biologically mediated degradation reactions.
Abiotic processes Approximately 25 of the
average oil spill on the open ocean evaporates.
In the gaseous state, hydrocarbons are readily
photooxidized. The dissolved fraction of
petroleum also is subject to photo-oxidation. The
largest sink for alkanes in the atmosphere is
reactions with OH and NO3 radicals (formation of
photochemical smog). Mono-aromatic hydrocarbons
react only with OH radicals, forming aldehydes,
cresols, and in the presence of NO,
benzylnitrates.
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Degradation of Organic Compounds
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Degradation of Organic Compounds
Biotic processes In soils and groundwater,
biologically mediated processes dominate. The
more water-soluble components of crude oil and
petroleum produces are most frequently reported
in groundwater downgradients from spills and
leaks. These hydrocarbons are biologically
reactive and their fate in the subsurface is
controlled by microbiological as well as
physical and chemical processes. Certain
microorganisms are able to degrade petroleum
hydrocarbons and use them as a sole source of
carbon and energy for growth.
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Degradation of Organic Compounds
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Degradation of Organic Compounds
Summation curves of oxygen consumption in soil
(S) contaminated with oil, which was mixed with
compost (C) in different ratios
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Degradation of Organic Compounds
Anaerobic processes Anoxic conditions frequently
develop in subsurface environments affected by
high concentrations of dissolved hydrocarbons
because of rapid aerobic biodegradation rates and
the limited supply of oxygen. In the absence of
oxygen, the oxidized forms of other inorganic
species, and some organic species such as humic
substances, are used by microorganisms as
electron acceptors. The most commonly available
electron acceptors in subsurface environments
include both solid (such as Fe and Mn oxides) and
dissolved (such as nitrate and sulfate) species.
In aquifers, as geochemical conditions change, a
sequence of reactions occurs, reflecting the
ecological succession of progressively less
efficient modes of metabolism.
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Degradation of Organic Compounds
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Degradation of Pesticides in Soils
The entire biocide is bioavailable directly after
application. Within a few days there is
reversible adsorption to soil particles.
Biomineralisation takes place in the dissolved
phase, which leads to the mobilisation of
adsorbed biocide constituents, where the
breakdown continues. Thus, there is a maximum for
the amount of bound biocide.
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Degradation of Organic Compounds
Behaviour (transport, transformation) of
pesticides in soil
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Degradation of Organic Compounds
Landfill leachate
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Degradation of Organic Compounds
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Degradation of Organic Compounds
BIODEGRADATION OF PCBs   As a result of their
very stable properties, PCBs are synthetic
compounds that are not readily degraded. The
degradation of these compounds entails difficult
mechanisms of chemical, biochemical or thermal
destruction. Biodegradation, that is, the
degradation of compounds by bacteria or other
microorganisms, is a slow yet possible method for
destroying PCBs in both aerobic and anaerobic
environments. It is the only process known to
degrade PCBs in soil systems or aquatic
environments. The specific processes involved are
aerobic oxidative dechlorination or hydrolytic
dehalogenation and anaerobic reductive
dechlorination. Theoretically, the biological
degradation of PCBs should result to give CO2,
chlorine and water. This process involves the
removal of chlorine from the biphenyl ring
followed by cleavage and oxidation of the
resulting compound. Persistence of PCBs in the
environment increases with the degree of
chlorination of the congener. The position of
chlorine atoms on the rings also affects the rate
of biodegradation A possible pathway for the
aerobic oxidative dehalogenation of PCBs
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Degradation of Organic Compounds
Biodegradation of pesticides DDT  
Concentration of DDT and degradation products in
southern Florida fishes in 1995.  Fish at sites 6
and 7 had multiple DDT degradation products
total DDT at all other sites was principally
p,p'DDE.