Environmental Toxicology
and Chemistry
Department of Environmental
and Molecular Toxicology
NCSU
©Chaves, Hofelt, Shea.
Predicting Environmental Fate and
Effects II
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Irreversible Reactions
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Hydrolysis
• RX + H2O = ROH + HX
• Neutral, acid and base hydrolysis.
• Nucleophilic displacement reactions
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Photolysis
• Direct and indirect photolysis.
• Results in transformations such as
isomerization, bond cleavage,
intramolecular rearrangement, among
others.
• Main reaction in atmosphere.
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Oxidation-Reduction Reactions
• oxidation means a loss of electrons:
– oxidizing agents are electrophiles
– net effect: either an increase in the oxidation
state of that chemical or the incorporation of
oxygen into the molecule.
• Reduction reactions involve an electron
donor known as the reductant and an
electron acceptor known as the oxidant.
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Biotransformations
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Predicting Environmental
Transformations
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Predicting Equilibria and Rates
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Modeling Environmental Fate
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Calculated Chemical Distribution in
a Hypothetical Pond
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Calculated Chemical Distribution in
the Environment
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Quantitative Structure-Activity
Relations (QSAR)
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Microcosms
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Microcosms
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Model Ecosystem
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Environmental Fate Models
• General steps:
– 1- Definition of the spatial and temporal scales and
the establishment of the environmental compartments
of interest.
– 2- Identification and quantification of the source
emissions.
– 3- Writing of the mathematical expressions for
advective and diffusive transport processes.
– 4- Quantification of the chemical transformation
processes
©Chaves, Hofelt, Shea.
©Chaves, Hofelt, Shea.
References
• 1-Crosby, D.G. Environmental Toxicology
and Chemistry. 2000. Oxford University
Press, New York.
• 2- Shea, D. Transport and Fate of
Toxicants in the Environment. In: Hodgson
and Levi (Eds), A Textbook of Modern
Toxicology, Second Edition, Appleton and
Lange, 1997.
©Chaves, Hofelt, Shea.