PRINCIPLES OF TOXICOLOGY

17 Properties and Effects of Natural
Toxins and Venoms
PROPERTIES AND EFFECTS OF NATURAL TOXINS AND VENOMS
WILLIAM R. KEM
This chapter will discuss
• Differences between poisons, toxins, and venoms
• Major sites and mechanisms of toxin action
• Important microbial, plant, and animal toxins
• Animal venoms and their active constituents
• Plants and animals causing contact dermatitis
• Strategies for treating intoxications and envenomations
We live in a world containing a wide variety of organisms—animal, plant, and microbial—possessing
substances that are potentially harmful to our health. Fortunately for most urban inhabitants,
the chances of developing morbid or fatal reactions to naturally occurring toxins are
relatively small. Still, even in an urban setting we are vulnerable to at least some natural toxins,
such as those occurring in foods, our ornamental plants, or our places of habitation. Furthermore,
as human populations expand into rural regions, they inevitably become more vulnerable to
poisonous creatures.
In this chapter we shall discuss some of the most common natural toxins, their mechanisms of
action, and some modern principles of their treatment.
17.1 POISONS, TOXINS, AND VENOMS
First we need to understand what is meant by the terms: poison, toxin, venom. A poison is any
substance or mixture of substances which can be life-threatening. Poisonous organisms either
secrete or contain one or more chemicals (toxins) that seriously interfere with normal physiological
functions. A toxin is a single substance with definable molecular properties that interferes with
normal function. Most toxins are exogenous substances made by an organism to adversely affect
another organism. However, even humans produce endogenous toxins (complement, defensins)
to resist attack by foreign organisms such as bacteria and viruses. Venoms are secretions
containing a mixture of biologically active substances, including enzymes, toxins, neurotransmitters,
and other compounds. They are generally used both for prey capture and as a chemical
defense against other predators. Some toxins are used solely as chemical defenses against
predators, and in these cases, the toxins are often released from relatively simple integumentary
glands, and may even be stored within visceral organs. One example of such a toxin is pufferfish
toxin, which will be discussed below.
Principles of Toxicology: Environmental and Industrial Applications, Second Edition, Edited by Phillip L. Williams, Robert C.
James, and Stephen M. Roberts.
ISBN 0-471-29321-0 © 2000 John Wiley & Sons, Inc.
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