Photo of coloured test tubes
Evidence shows that chemicals in the environment can cause cancer [Image: Armin Kübelbeck - Wikimedia Commons]

Cancer causes: beyond the usual suspects

24 November, 2011

When it comes to cancer causes, most of us have heard the standard “genes and lifestyle” arguments.

The problem with focusing on these ‘usual suspects’ is that neither one can can be consistently linked to the development of cancer.

There has, for example, been considerable interest in the genetic causes of cancer for many years now. The theory here is that if we understand which genes are responsible for uncontrolled cell division, then it might be possible to treat the cancerous cells. In addition, there is the notion that many cancers are genetically inherited and that the disease is therefore a problem of heredity.

However a landmark study of 90,000 Swedish twins showed that the environment is the main cause of cancer in that if a twin got cancer the other did not necessarily get it, showing that environmental factors are mainly to blame.

Looking at lifestyle

It is also known that a relatively small percent of breast cancers are inherited. Breast cancer is a relatively uncommon disease in Asian women but when they adopt Western habits the incidence starts to rise thereby indicating that it is something external to them that is causing the disease.

It is clear that certain lifestyle habits – for example, smoking, excess alcohol and sun-bathing – expose people to an increased risk of cancer.

However, it is also becoming increasingly apparent that the causes of cancer are not only due to lifestyle choices. For example, the number of people getting lung cancer who do not smoke is rising and this may be because of atmospheric pollution.

Sunshine is becoming increasingly pervasive due to chemicals damaging the ozone layer that normally protects us from harmful ultraviolet rays. Likewise, a diet rich in animal fats may expose us to high levels of lipophilic (fat loving) carcinogens which may not have been present in pre-industrial times.

Chemicals: a neglected area

We believe that the real problem with focusing on “genes and lifestyle” argument is that they let another real enemy – harmful synthetic chemicals – off the hook.

There is now a large and ever increasing scientific literature clearly documenting links between chemicals and cancer. Why this is evidence is often ignored or downplayed should be of major concern to anyone genuinely concerned about disease prevention.

The fact is, cancer was a rare disease in pre-industrial societies.

Dr Albert Schweitzer, the celebrated physician and humanitarian, wrote that, ‘on my arrival in Gabon in 1913 I was astonished to encounter no case of cancer… I can not, of course, say positively that there was no cancer at all, but like other frontier doctors, I can only say that if any cases existed they must have been quite rare’.

An Alaskan doctor reported that in his thirty-six years of practice he had never seen a case of malignant disease among the truly primitive Eskimos and Indians although it occurred frequently when they become modernised. Since 1840, similar findings have been reported by doctors for native people throughout the world.

As Dr. Schenk observed, ‘it is the nature and essence of industrial civilisation to be toxic in every sense. We are faced with the grim prospect that the advance of cancer and of civilisation parallel each other.’ In 1960, Professor Rene Dubois wrote that, ‘certain diseases such as dental caries, arteriosclerosis and cancers are so uncommon among certain primitive peoples as to remain unnoticed – at least as long as nothing is changed in the ancestral way of life’.

Enter industrialisation

Clearly, something about our industrial way of life changed all that. Like heart disease, diabetes and obesity, cancer is primarily a disease of civilization.

Many of these chemicals are truly artificial in that their structure is entirely novel and not found naturally. There is considerable confusion here. For example Vitamin C (ascorbic acid) whether found in oranges or made by the chemical industry is always structurally the same.

On the other hand the anti-bacterial Triclosan found in soaps and toothpaste is an artificially chlorinated compound and no such compound exists in the natural world. Triclosan is reportedly neither carcinogenic nor mutagenic but its structural similarity to a dioxin contaminant in Agent Orange (used as a defoliant during the Vietnam War) gives cause for very close monitoring of this household product.

Many of these artificial substances are persistent and because they are not easily metabolised they bioaccumulate in our bodies. An enormous group of such chemicals are the organochlorines which are made by chemically combining chlorine to carbon containing molecules.

As a general rule, organochlorines are much more toxic than their unchlorinated counterparts. Organochlorine compounds are found everywhere: tap water, dry cleaning fluid, disinfectants, cleaning products, toothpaste, etc.

No part of the globe is free of synthetic chemicals

It is estimated that there are about 35 tons of one pesticide alone, atrazine, in Lake Erie in North America. This single example clearly demonstrates that huge quantities of man-made chemicals are entering the global ecosystem.

Poisoned Beluga whales have been washed up dead in the St Lawrence river; one whale was so contaminated that its body burden of dangerous chemicals were ten times more than the level necessary to qualify as hazardous waste under Canadian law.

In science it is common to compare a population of animals or people being investigated with another ‘control’ population. “Where,” it was asked by scientists, “could we find an uncontaminated control population with which we could compare body burdens of chemicals in people from industrialised countries?

They looked at the blood and fat of Eskimos and Inuits living in the Arctic Circle expecting to find very low levels of synthetic chemicals. Instead, scientists have found that these unfortunate people had very high levels of toxic chemicals in their bodies.

This contamination is due to two factors: One is a process called global distillation by which chemicals accumulate in colder parts of the globe; the other is because of the high fish and animal fat diet that Arctic dwellers eat – chemicals are concentrated in the food chain.

Chemicals in people

Each one of us carries at least 250 chemical contaminants. Many artificial chemicals evade metabolic degradation and accumulate in our tissues particularly body fat. Perhaps of greatest concern is that the breast feeding infant is right at the top of the food chain and residual toxins present in the mother pass across to the child in her milk.

Thus a very important activity which provides essential nutrients to the growing child, confers immune protection and promotes bonding also becomes a source of toxic chemicals. This problem is made even worse because small children lack important de-toxification enzymes in the liver.

The effects of chemicals on human health

Human beings are themselves composed of thousands of chemical substances that serve different functions. Ingested chemicals are either assimilated or eliminated. Chemicals are toxic when they interfere with the normal functioning of the body. Alcohol is a toxin which can, fortunately, be broken down and eliminated; but excessive, chronic consumption of alcohol can lead to cirrhosis and liver cancer.

From time to time there are well-publicised reports in the media about industrial accidents where large quantities of toxic chemicals are suddenly released into the environment. Seveso, Bhopal and Chernobyl have become synonyms for such accidents. But the effects of chronic, low dose ingestion of toxic chemicals on human health can be much subtler.

For example, Mexican children raised where intensive agriculture is practised suffer from significant cognitive impairment when compared to children living in areas where traditional agriculture is practised.

Farmers – the canaries in the coal mine?

In looking at cancer in the general population it is very hard to determine the effect of the chemicals to which we are exposed because we are exposed to so many during our lifetime. Probably the best correlation between chemicals and cancer has been seen in farmers.

Farmers are generally more healthy than the average person. They have low rates of heart disease and other ailments. However, for the last thirty years or so, they have experienced high rates of leukaemia, non-Hodgkin’s lymphoma and cancers of the brain and prostate. Animal and epidemiological studies have linked these types of cancer to exposure to pesticides and solvents.

In the 1940s American farmers used about 22 thousand metric tonnes of insecticides. Now more than 450 thousand metric tonnes are used each year. 53 carcinogenic pesticides are registered for the use on major crops such as apples, tomatoes and potatoes. Approximately 34 pesticides are used for lawn treatment at rates up to five times greater than in agriculture.

Furthermore, since 1976 several human studies have found a strong association between increased body levels of pesticides and breast cancer. Particularly noteworthy, was that the breast cancer rate in Israeli women immediately dropped in 1978 when three pesticides known to accumulate in breast tissue were banned.

Biological vs chemical hygiene

Since the 19th century, with the discoveries of microbiology, we have been taught about the importance of biological hygiene, but we have been taught very little about chemical hygiene. These days, most households generate large quantities of chemicals which are either flushed down drains or sprayed on furniture and work surfaces to eliminate germs.

We believe that what is urgently needed is an awareness of the importance of chemical hygiene: We must use chemicals sparingly and carefully, and in particular we must not dump them willy-nilly into our air, water and land.

The proper, systematic education of people regarding the importance of chemical hygiene could well be as vital for human health as the discovery of antibiotics and vaccines.


  • Jamie Page is Chief Executive of the Cancer Prevention Society.
  • For useful factsheet with a list of review papers on chemicals and cancer see here.