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Matt Ridley is the author of provocative books on evolution, genetics and society. His books have sold over a million copies, been translated into thirty languages, and have won several awards.

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Cancer, chemicals, Carson and smoking

Rachel Carson, in her hugely influential book Silent Spring, wrote that she expected an epidemic of cancer caused by chemicals in the environment, especially DDT, indeed she thought it had already begun in the early 1960s:

``No longer are exposures to dangerous chemicals occupational alone; they have entered the environment of everyone-even of children as yet unborn. It is hardly surprising, therefore, that we are now aware of an alarming increase in malignant disease.

The increase itself is no mere matter of subjective impressions. The monthly report of the Office of Vital Statistics for July 1959 states that malignant growths, including those of the lymphatic and blood-forming tissues, accounted for 15 per cent of the deaths in 1958 compared with only 4 per cent in 1900. Judging by the present incidence of the disease, the American Cancer Society estimates that 45,000,000 Americans now living will eventually develop cancer. This means that malignant disease will strike two out of three families. The situation with respect to children is even more deeply disturbing. A quarter century ago, cancer in children was considered a medical rarity. Today, more American school children die of cancer than from any other disease. So serious has this situation become that Boston has established the first hospital in the United States devoted exclusively to the treatment of children with cancer. Twelve per cent of all deaths in children between the ages of one and fourteen are caused by cancer. Large numbers of malignant tumors are discovered clinically in children under the age of five, but it is an even grimmer fact that significant numbers of such growths are present at or before birth. Dr. W. C. Hueper of the National Cancer Institute, a foremost authority on environmental cancer, has suggested that congenital cancers and cancers in infants may be related to the action of cancer-producing agents to which the mother has been exposed during pregnancy and which penetrate the placenta to act on the rapidly developing fetal tissues.''

Carson was wrong about this. Not only has DDT proved not to be a carcinogen, but the cancer epidemic caused by exposure of the general public to chemicals has wholly failed to materialise. Study after study has found that there is no increase in cancer incidence or death in the general population, when corrected for age, to be explained by man-made chemicals. Those, like Paul Ehrlich, who confidently predicted that the lifespan of Americans would fall to 42 years by the end of the twentieth century thanks to such cancer epidemics, were proved badly wrong.

Here are the charts of cancer deaths for men and women, adjusted for age, in the United States since the 1930s.

The one that stands out, of course, is lung cancer. The rapid increase in lung cancer (boosted surely changing diagnosis in the early years) was caused by the increase in smoking, of course. Almost nobody now challenges that. But they did once. Indeed, one of the most vociferous opponents of the theory that smoking causes lung cancer was none other than Carson's mentor, William Hueper.

So obsessed was Hueper with his notion that pesticides and other synthetic chemicals were causing an epidemic of cancer and that industry was covering this up, that he bitterly opposed the suggestion that smoking take any blame - as an industry plot.

Here he is writing a paper called Lung Cancers and their Causes in 1955 in CA, a cancer journal for clinicians

1. The total epidemiological, clinical, pathological, and experimentalevidence on hand clearly indicates that not a single but severalif not numerous industrial or industry-related atmospheric pollutantsare to a great part responsible for the causation of lung cancer.

2.While the available data do not permit any definite statementas to the relative importance of the various recognized respiratorycarcinogens in the production of lung cancers in the generalpopulation, they nevertheless unmistakingly suggest that cigarettesmoking is not a major factor in the causation of lung cancernor had it a predominant role in the remarkable increase ofthese tumors during recent decades.

3. In view of the fact thatnot only a great deal of the existing circumstantial epidemiologicalevidence but also pratically the entire factual and conclusiveevidence available on exogenous respiratory carcinogens areeither of occupational origin or point to industry-related factors,it would be most unwise at this time to base future preventivemeasures of lung-cancer hazards mainly on the cigarette theoryand to concentrate the immediate epidemiological and experimentalefforts on this evidently overpropagandized and insufficientlydocumented concept.

When environmentalists want to attack a sceptic these days, they quite frequently accuse him or her of being the kind of person who would have defended the tobacco lobby - in some cases with justification. So it is ironic to find that possibly the most iconic and original text of the entire environmental movement, Silent Spring, was built on the work of a fervent tobacco defender. Hueper is quoted frequently throughout Carson's book.

By the way, in my book I say that Rachel Carson `expected DDT "to cause practically 100 per cent of the human population to be wiped out from a cancer epidemic in one generation"'. This is inaccurate: I slipped up. I relied on an article in a magazine called Front Page in July 2003 for this quotation, and unusually I did not check it with Carson's original text. Alerted by a reader, Ed Darrell (thanks!) I have now checked Carson's Silent Spring, and while Carson strongly implies that she does indeed expect a major mortality from cancer caused by DDT, what she actually wrote is the following:

In the springof 1961 an epidemic of liver cancer appeared among rainbow trout in many federal, state, and private hatcheries. Trout in both eastern and western parts of the United States were affected; in some areas practically 100 per cent of the trout over three years of age developed cancer. ...The story of the trout is important for many reasons, but chiefly as an example of what can happen when a potent carcinogen is introduced into the environment of any species. Dr. Hueper has described this epidemic as a serious warning that greatly increased attention must be given to controlling the number and variety of environmental carcinogens. 'If such preventive measures are not taken,' says Dr. Hueper, 'the stage will be set at a progressive rate for the future occurrence of a similar disaster to the human population.'

My book criticises Carson and her followers for their exaggerated pessimism which led to the phasing out of DDT as an anti-mosquito weapon and hence led directly to the resurgence of malaria. This is a story that has been well told in many places and deserves to be better known. But I find many of DDT's defenders then go on to make a claim that I do not believe is correct, namely that DDT had no impact on birds, and that the story that it led to the thinning of eggshells in birds at the end of long food chains, such as falcons and pelicans (and also damaged the reproduction of predatory mammals such as otters), is false. I simply do not accept that. The evidence of bioaccumulation in fat, of eggshell thinning and of DDT's role in the decline of raptors and other predatory birds in the 1960s seems to me fairly strong, though not overhwelming. The ending of indiscriminate and widespread spraying of DDT is probably a good thing.

It is, fortunately, very easy to use DDT against malarial mosquitoes without poisoning birds. The solution is to use it sparingly on the inside walls of houses, where anopheline mosquitoes rest during the day. This targets the pest while not allowing the pesticide to contaminate the food chain in nearby ecosystems. The best of both worlds.