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Introduction to Toxicology (Ernest Hodgson)

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CHAPTER 1

Introduction to Toxicology
ERNEST HODGSON

1.1 DEFINITION AND SCOPE, RELATIONSHIP TO OTHER SCIENCES,
AND HISTORY
1.1.1

Definition and Scope

Toxicology can be defined as that branch of science that deals with poisons, and a
poison can be defined as any substance that causes a harmful effect when administered,
either by accident or design, to a living organism. By convention, toxicology also
includes the study of harmful effects caused by physical phenomena, such as radiation
of various kinds and noise. In practice, however, many complications exist beyond
these simple definitions, both in bringing more precise meaning to what constitutes
a poison and to the measurement of toxic effects. Broader definitions of toxicology,
such as “the study of the detection, occurrence, properties, effects, and regulation of
toxic substances,” although more descriptive, do not resolve the difficulties. Toxicity
itself can rarely, if ever, be defined as a single molecular event but is, rather, a cascade
of events starting with exposure, proceeding through distribution and metabolism, and
ending with interaction with cellular macromolecules (usually DNA or protein) and
the expression of a toxic end point. This sequence may be mitigated by excretion and
repair. It is to the complications, and to the science behind them and their resolution,
that this textbook is dedicated, particularly to the how and why certain substances
cause disruptions in biologic systems that result in toxic effects. Taken together, these
difficulties and their resolution circumscribe the perimeter of the science of toxicology.
The study of toxicology serves society in many ways, not only to protect humans
and the environment from the deleterious effects of toxicants but also to facilitate the
development of more selective toxicants such as anticancer and other clinical drugs
and pesticides.
Poison is a quantitative concept, almost any substance being harmful at some doses
but, at the same time, being without harmful effect at some lower dose. Between
these two limits there is a range of possible effects, from subtle long-term chronic
toxicity to immediate lethality. Vinyl chloride may be taken as an example. It is a
potent hepatotoxicant at high doses, a carcinogen with a long latent period at lower
A Textbook of Modern Toxicology, Third Edition, edited by Ernest Hodgson
ISBN 0-471-26508-X Copyright  2004 John Wiley & Sons, Inc.

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INTRODUCTION TO TOXICOLOGY

doses, and apparently without effe...
CHAPTER 1
Introduction to Toxicology
ERNEST HODGSON
1.1 DEFINITION AND SCOPE, RELATIONSHIP TO OTHER SCIENCES,
AND HISTORY
1.1.1 Definition and Scope
Toxicology can be defined as that branch of science that deals with poisons, and a
poison can be defined as any substance that causes a harmful effect when administered,
either by accident or design, to a living organism. By convention, toxicology also
includes the study of harmful effects caused by physical phenomena, such as radiation
of various kinds and noise. In practice, however, many complications exist beyond
these simple definitions, both in bringing more precise meaning to what constitutes
a poison and to the measurement of toxic effects. Broader definitions of toxicology,
such as “the study of the detection, occurrence, properties, effects, and regulation of
toxic substances,” although more descriptive, do not resolve the difficulties. Toxicity
itself can rarely, if ever, be defined as a single molecular event but is, rather, a cascade
of events starting with exposure, proceeding through distribution and metabolism, and
ending with interaction with cellular macromolecules (usually DNA or protein) and
the expression of a toxic end point. This sequence may be mitigated by excretion and
repair. It is to the complications, and to the science behind them and their resolution,
that this textbook is dedicated, particularly to the how and why certain substances
cause disruptions in biologic systems that result in toxic effects. Taken together, these
difficulties and their resolution circumscribe the perimeter of the science of toxicology.
The study of toxicology serves society in many ways, not only to protect humans
and the environment from the deleterious effects of toxicants but also to facilitate the
development of more selective toxicants such as anticancer and other clinical drugs
and pesticides.
Poison is a quantitative concept, almost any substance being harmful at some doses
but, at the same time, being without harmful effect at some lower dose. Between
these two limits there is a range of possible effects, from subtle long-term chronic
toxicity to immediate lethality. Vinyl chloride may be taken as an example. It is a
potent hepatotoxicant at high doses, a carcinogen with a long latent period at lower
A Textbook of Modern Toxicology, Third Edition, edited by Ernest Hodgson
ISBN 0-471-26508-X Copyright
2004 John Wiley & Sons, Inc.
3
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