London -- Scary headlines recently announced a study claiming that a pesticide causes prostate cancer and birth defects.

Predictably, the study on banana plantations in the Caribbean islands of Martinique and Guadaloupe was seized on by environmentalists, in vindication of their beliefs about the dangers of agricultural chemicals.

But, in spite of its alarmism, the study found no relationship between pesticide exposure and adverse health effects. Such hysteria does far more harm than good.

Some perspective is required. In the UK, for example, prostate cancer is detected in over half of autopsies on those dying of unrelated causes.

In the USA, autopsy studies reveal microscopic evidence of the disease in 34% of 40-49 year olds.

But chlordecone has been banned in both countries since 1977: just because it is widespread in Martinique and Guadeloupe you cannot assume that exposure causes disease. For there to be a link, a relationship would have to be established between pesticide exposure and the incidence of cancer.

No such link has been established and, importantly, no mechanism whereby the pesticide might produce the tumour has been found.

The same applies to birth defects. In 1976, a horrific industrial accident in Seveso, Italy, released a large amount of dioxin into the atmosphere. Environmentalists claimed that there would be a massive increase in the number of birth defects.

Although the dioxin did cause skin problems, subsequent studies showed no relationship between dioxin exposure and birth defects. 

In any study where pesticides or other chemicals are claimed to be the cause of disease, it is necessary to consider other factors which may confuse the picture, such as age, family history and smoking.

These will be nearly always be more important in producing disease than any chemical exposure. But researchers who examine environmental causes of disease often do not have or do not use such information--or even information about the duration and extent of exposure to the chemical in question.

Without this solid data, any conclusions must be treated with extreme caution.

But campaigners often choose the opposite interpretation. Because it is never possible to say with certainty that any specific chemical does not cause cancer, and because many chemicals do cause cancer when given in high doses to rodents, they say that all chemicals that might perhaps cause cancer should be banned.

This ignores the cost of such a ban. Without pesticides, about one third of any crop would be lost to disease, infestation or predation.

In fact, the risk of not using pesticides and other chemicals is far higher than the small and hypothetical risks of using them.

For instance, chemicals have enabled far more people to have access to inexpensive fresh fruit and vegetables: studies show that eating more of these improves the chance of defending yourself against diseases--including cancer.

The risk of contracting disease due to ingesting pesticide residue, meanwhile, is hypothetical.

Moreover, by increasing crop yields, pesticides and other agricultural chemicals reduce pressure to convert marginal land to agriculture. So, even though some of this cropland may support less wildlife, there will be more land left for wildlife overall.

Sadly, campaigners continue to assert that all chemicals are bad for human health and the environment, encouraging the popular belief that the presence of chemicals in food is bad for health.

As a result, there has been a push to limit the use of chemicals in agriculture, in favour of "organic” methods.

of all the dietary pesticides that humans eat are natural. Many of them are equally or more carcinogenic than common synthetic pesticides.

Professor Bruce Ames, a leading expert on cancer and ageing, points out that a cup of coffee contains as much carcinogenic material as all the synthetic dietary pesticides a normal person consumes in a year’s worth of non-organic fresh fruit and vegetables. Prof. Ames still drinks coffee.

Hungry human beings should in fact be more fearful of some "all-natural” things like grasshoppers, fungi and locusts that have throughout human history stifled food production and led to malnutrition.

Modern agricultural chemicals have overcome these problems, making food more abundant and cheap, including in poor countries.

So by banning pesticides, we would be less well-fed and thus likely to be more susceptible to disease.

Modern agricultural technologies have ensured the regular delivery of cheap and nutritional food to billions. Removing chemicals from the process would see yields plummet and the price of fruit and vegetables would soar, leaving only the rich with the option of a healthy life-prolonging diet.

Of course, pesticides must be used safely and, under certain circumstances, it may be appropriate to regulate their use. But alarmist claims of the kind made about pesticides and health in the Caribbean undermine public confidence in chemicals and lead to misguided policies that would cause more harm to the environment and health.

Professor Sir Colin Berry is professor of morbid anatomy and histopathology at Queen Mary College, University of London.