Title: Toxicology and human health

Key words: poisons, mercury, cadmium, cancer, chemical exposure, environmental pollution, synthetic chemicals, biological mechanisms, scientific consensus, government legislation, plants, fungi, bacteria,

Date: April 2001

Category: Directory

Type: Article

Author: Simon Wolff

Toxicology and human health

Calculated Risks: The Toxicity and Human Health Risks of Chemicals in Our Environment by Joseph V. Rodricks, Cambridge University Press, pp 256, Pounds Sterling

Poisons are big business. They are the stuff of big disasters, big money, big vested interests, big campaigns and big emotions. Toxicology, the study of poisons, affects virtually every area of modern life. But it is rare to find an intelligent and relaxed book that discusses the complex issues with such critical dispassion and accuracy.

Toxicology is a new field but has noble and ignoble origins dating back centuries. Probably since the time of early humans acute poisons have been understood as foods to be avoided, and used as ways of immobilising prey and disposing of enemies or oneself. It is only more recently that we have learnt that not all poisons act rapidly. Some poisons, such as mercury and cadmium, exert their damage in slow ways so that the connection between cause and effect is not immediately obvious. Other substances and chemical exposures may appear normal and innocuous but contribute to cancers decades after the first exposure.

We have also learnt about the side effects of drugs, the impact on health of environmental pollution and the potential dangers associated with synthetic chemicals. Modern toxicology assesses these risks and tries to understand the biological mechanisms by which chemical agents cause damage. Rodricks tells us in carefully developed detail about the methodologies involved; the types of understanding needed; as well as the sociology and psychology involved in the development of scientific consensus and governmental regulation.

The author also draws sharp but polite attention to the intellectual poverty of dividing the natural and synthetic world into 'toxic' and 'nontoxic'. For everything is a poison; dependent upon the dose, the route of administration and the ways in which the human body interacts with the substance and disposes of it. A cigarette, for example, contains enough nicotine to kill a person if extracted and injected, yet no smoker dies of acute nicotine poisoning. And, while it is true that many synthetic chemicals are toxins, not all toxins are synthetic. When it comes to chemical warfare, for example, plants, fungi and bacteria make human efforts at chemical mass destruction look feeble.

Rachel Carson's Silent Spring (1962) drew attention to the possibility of ecological degradation engendered by the use of synthetic pesticides but failed to generate concern about the huge armoury of cytocidal agents produced by plants in the silent war with their predators. For example, yams produce soapy oestrogens in their leaves to control local populations of wild pigs through involuntary contraception. The artemisia family (mugworts) produce powerful and chemically complex anti-malarials, not for human benefit but to control the roundworms that would otherwise infest their roots. Hemp synthesises tetrahydrocannabinol to discourage cattle from eating it - they, in contrast to humans, do not like being stoned.

Our food contains thousands of substances that have the potential to knock us dead, cause malignancy, or render us unreproductive. But they don't. Yet the introduction of synthetic antioxidants, added to foodstuffs to give them a longer shelflife, coincided with a precipitous decrease in the incidence of stomach cancer. So many antioxidants can act as antitoxins but food regulators, spurred on by zealous campaigners, try to ban these compounds. If we were consistent in our attitudes to risk from chemicals, there would be very few foodstuffs we would be allowed to eat.

Rodricks' book needs to be read by every medical scientist with any concern for public health issues as well as by environmental and food safety campaigners. It will sharpen debating skills enormously, broaden understanding of risk through chemicals and reveal not a few idiocies. Rodricks tells the scientists, the campaigners and the concerned citizens what they need to know. And they won't even need a dictionary. Dose-response curves, thresholds, environmental epidemiology and drug metabolism are all covered in simple and, at times, humorous terms. Toxicology is delightful - an art as well as science. Rodricks covers both.

Simon Wolff lectures in toxicology at University College London.

From New Scientist magazine, vol 135 issue 1835, 22/08/1992, page 37

© Copyright New Scientist, RBI Ltd 2000