Environmental Geosciences
Human Interactions with the
Environment
Organics
Andrea Koschinsky
Distribution and Transformation of Organic
Compounds
Basic principles of pollutant distribution and transformations. The factors controlling
chemodynamics include Henry’s constant, sorption/distribution coefficients,
bioconcentration factor, and KOW.
Distribution and
Transformation
of Organic
Compounds
Materials properties
and environmental
behavior
Transport and Sorption of Organic
Compounds
Transport and Cycling of Organic Compounds
Transport and Cycling of Organic Compounds
Transport and Cycling of Organic Compounds
Transport and Sorption of Organic
Compounds
KOA = octanol-air partitioning coefficient
PL = vapor pressure of the subcooled liquid
TC = condensation temperature
Transport and Sorption of Organic
Compounds
CFCs = Chlorofluorocarbons
PCDD = polychlorinated dibenzo-p-dioxin, PCDF = polychlorinated dibenzofuran
Transport and Cycling of Organic Compounds
Transport and Cycling of Organic Compounds
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.
Degradation of Organic Compounds
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.
Aerobic processes
Oxygen is the preferred electron acceptor by microorganisms because of the high-energy
yield of these processes. Aerobic degradation of hydrocarbons can occur when indigenous
populations of bacteria capable of aerobic degradation of hydrocarbons are supplied with
molecular oxygen and nutrients required for cell growth. Studies involving complex mixtures
of hydrocarbons have demonstrated that microorganims can degrade most of the
hydrocarbons present in gasoline.
Degradation of Organic Compounds
Degradation of Organic Compounds
Summation curves of oxygen consumption in soil (S) contaminated with oil, which was
mixed with compost (C) in different ratios
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.
Degradation of Organic Compounds
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.
Degradation of Organic Compounds
Behaviour (transport, transformation) of pesticides in soil
Degradation of Organic Compounds
Landfill leachate
Degradation of Organic Compounds
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
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.