The Poison Paradox: Chemicals as Friends and Foes

By John Timbrell | Go to book overview

6
Natural Born Killers
Poisonous Chemicals Designed
by Nature

Many people think of chemicals as not only intrinsically dangerous but also exclusively man-made and hence unnatural. Chemicals are found throughout the natural world. The world is naturally a chemical environment, both the earth itself and the animals and plants on it being made from chemicals. As we have seen, minerals such as compounds of arsenic, cadmium, lead, and mercury all occur naturally and have at times been responsible for poisoning.

In addition to these substances and the normal constituents of living things, such as DNA, fats, and sugars, there are many toxic chemicals manufactured by plants, animals, and micro-organisms. Some of these will be explored later (see pp. 239–57). These natural but synthetic chemicals are often used by the plant or animal for protection, as they engage in chemical warfare against predators. Plants may be trying to stop animals such as birds or insects eating their berries, seeds, or leaves. For example, many fruit kernels and pips contain cyanides, while the deadly nightshade plant produces atropine in its berries. Both can be lethal to humans. Thus many plants produce natural insecticides.

There are a very large number of chemicals that have been identified in plants and many thousands that have not. Some are toxic, others benign. It is not possible within the limits of this book to consider more than one or two. It is important to note that some extremely toxic chemicals are found naturally and do contribute to human disease and poisoning (see also pp. 239–57). Some of these chemicals may have only a single target species; others will be toxic to most. The animals that are predators for these plants can become immune, presumably, through a process of natural selection.

Knowledge of the toxic effects of some of the chemicals in plants have

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