Loomis's Essentials of Toxicology

A. Wallace Hayes, Tao Wang, Darlene Dixon, Ted A. Loomis

• Publisher: Academic Press
• Year: 2019
• ISBN:
  9780128159224
• Edition: 5
• Topic: Medicine
• Subtopic: Toxicology

Loomis's Essentials of Toxicology, Fifth Edition, provides the information on the harmful biologic effects associated with exposures to chemicals of all types. The scope of this book includes a discussion of the major types of chemicals involved, their general properties and detrimental biologic effects, the methods used to demonstrate these effects, the basis for clinical diagnosis, and therapy for the harmful effects of chemicals on humans. Individual examples are used to demonstrate the principle discussed. This reference volume will be an invaluable resource for both toxicologists and graduate and advanced undergraduate students in toxicology and public health.

• Provides a revised and updated edition of one of the "gold" works in the field
• Includes both principles and methods
• Requires minimal background in chemistry and biology
• Expanded Information Sources in Toxicology

Chapter 1

Introduction, scope, and principles

Abstract

The harmfulness or safeness of any chemical is related primarily to the amount of that compound in the body. One of the most fundamental observations of any biologic effect of a chemical agent is the relationship between the dose (or concentration) and the response. Thus, research in toxicology focuses on studying the adverse effects of chemicals on biologic cells, tissues, systems, and pathways. The field most closely related to modern toxicology is pharmacology, for a pharmacologist must understand not only the beneficial effects of chemicals but also the harmful effects of those chemicals that may be put to therapeutic use. The environment serves as both a supply source and a dump site for chemicals and their derivatives, and translocates each agent within the environmental pool. Exposure to chemicals in the environment and the public health consequences are continuing sources of concern in toxicology. However, toxicology's central concern lies in the evaluation of potential adverse effects of chemicals on humans. Academia, government agencies, and industry expend considerable effort and money in determining the mode/mechanisms of chemical-biological interactions. Currently, there are more than a million chemical entities to which the human population could be exposed. In spite of the multitude of chemicals that are potentially harmful, only a few have been adequately documented as causative of serious health problems in humans.

Keywords

Chemicals; Toxicology; Compounds; Effects; Environment; Harmful

Early in the days of the development of civilization, man in his quest for food must have attempted to eat a variety of materials of both botanical and animal origin. Through this experience, it is likely that he found that certain substances produced varying degrees of illness or even death. Other materials with a better outcome soon became a desirable form of food. Therefore, it seems reasonable to believe that humans soon recognized that there were harmful and beneficial consequences associated with taking materials into their bodies. All such materials could be placed in two broad classes, one of which was safe and the other harmful. The word “poison” would be the term used to describe those materials or chemicals that were distinctly harmful to the body, and “food” would be the term used for those materials that were beneficial and necessary for the body to function. This concept involving the division of chemicals into two categories has persisted to the present day and, as such, serves a useful purpose in society.

With the advancement of society and sciences, people recognize that there are degrees of harmfulness and safeness for any chemical. Even the most innocuous of substances, when taken into the body in sufficient amounts, may lead to undesirable effects. In contrast to this, the most harmful of all chemical agents can be taken into the body in sufficiently small amounts so that there will be no untoward effect from such chemicals. It is apparent that the harmfulness or safeness of a chemical is related primarily to the amount of that compound in the body. The most important factor that determines the effect of a chemical compound is the quantity of the compound that comes in contact with a biologic system. This quantity of the compound is commonly called the “dose.” (Dose may be expressed using a variety of terminologies and is further discussed in the next chapter.) As the dose is increased from minimal to maximal levels, the response, whether it be beneficial or harmful, is a graded response and is related to progressive changes in the dose over time. One of the most fundamental observations of any biologic effect of a chemical agent is the relationship between the dose (or concentration) and the response. Thus, research in toxicology focuses on studying the adverse effects of chemicals on biologic cells, tissues, systems, and pathways.

The word “toxic” may be considered synonymous with harmful in regard to the effects of chemicals. Two additional terms related to the words toxic and poison are toxin (naturally occurring toxic materials) and toxicant (all toxic materials whether from nature or man-made). Many chemicals are nonselective in their action to exert harmful effects on all living matter. In contrast to this, a given chemical may selectively produce harm only on specific organisms, cells, or pathways.

When a chemical is said to be toxic, the average person interprets this to mean that it would have a harmful or undesirable effect on humans, regardless of the amount. This may not be true when the toxicologist uses the words toxic or toxicity because what may be harmful to one species may be relatively harmless to another species. In fact, a chemical that is toxic to some organisms may be desirable as far as man is concerned. For example, a mosquito repellent is harmful or even lethal to mosquitoes but relatively harmless to humans and, therefore, indirectly beneficial and desirable to mankind. For this reason, we can make use of chemicals to our advantage. Therefore, if the term toxic or toxicity is used, it is necessary to identify the biologic mechanism on which the harmful effect is produced. Toxicity is a relative property of a chemical and may be directly or indirectly desirable or undesirable as far as man is concerned, but t...