Geology Reference
In-Depth Information
petrogenic sources vs. pyrolytic sources (both natural and anthropogenic)
for aromatic hydrocarbons in soil/sediment systems.
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6.3 THE FATE OF ORGANIC CONTAMINANTS
There are thousands of organic chemicals entered into the international
databases as part of legislative programmes aimed at assessing the risk
they pose to human health and the environment. For example, in the
European Union, the European Inventory for Existing Chemical Sub-
stances and the European List of Notified Chemical Substances include
over 100,000 commercial substances.
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Similarly in the US, the Office for
Pollution Prevention and Toxics (OPPT) as part of the US-Environmental
Protection Agency (EPA) maintains lists of high-production volume
chemicals as well as persistent bioaccumlative toxins (PBTs). The increas-
ing demand for risk assessment to examine substances with respect to their
environmental persistence, ability to bioaccumulate and potential for
toxicity, increases the demand for reliable physical-chemical property
data, upon which to conduct environmental fate and degradation studies.
In this respect, a risk assessment is conducted to ascertain the likelihood or
probability of some harm arising to either humans or the environment due
to exposure to that chemical substance. In order to assess exposure and
understand chemical fate, then intimate knowledge of both the chemical
use (quantity released) and behaviour (environmental transport, partition-
ing and transformation/degradation) are required. As Schwarzenbach
et al.
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have so elegantly described in their comprehensive text on EOC;
organic chemicals once present in the environment are subject to essen-
tially two types of process. The first involves their environmental transport
within, and transfer between, environmental phases and the second in-
volves their chemical alteration (transformation/degradation) driven by
chemical and/or biological processes. In reality, within any given environ-
mental system, these processes may occur simultaneously and different
processes may strongly influence one another.
6.4 CHEMICAL PARTITIONING
The transfer of chemicals between two or more environmental com-
partments or phases can be described by equilibrium partitioning, and
knowledge of this partitioning is essential for understanding and de-
scribing chemical fate in the environment. Chemical partitioning takes
place between adjacent phases such as between a solid and a liquid
(dissolution), a liquid and a gas (volatilisation), a solution and a solid
surface (adsorption) or a solution and an immiscible liquid (solvent
