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The return of Killer Chlorine

Just when you thought it was safe to go back in the water

Numberwatch After many mind-sapping years of trawling through the morass of health scare stories, I formulated a number of laws, one of which was the Law of Beneficial Developments:

The intensity of the scaremongering attack on any new development is proportional to the level of benefit that it endows.

Unbelievably, the Chlorine Scare has returned. According to the science editor of the Daily Telegraph, Babies exposed to chlorinated water are at risk of heart problems.

The first chestnut here is the appearance of a Trojan Number, so called because it is the stratagem by which authors infiltrate their findings into the columns of the media. In this case it is an impressive 400,000, which is the number of babies said to be involved in the study. In fact, almost all of them have no part in the study at all, as they are normal, healthy births.

As I wrote in a book called Sorry, Wrong Number! in 2000, chlorine is essential to life on earth, not only in the form of its sodium salt, but as a constituent of more than more than 1500 vital compounds in plants and animals, including our digestive juices. The chlorination of drinking water has saved more human lives than any other hygienic measure.

However in 1991, Greenpeace activist Christine Houghton said: "Since its creation, chlorine has been a chemical catastrophe. It is either chlorine or us." Even by Greenpeace standards this was a pretty remarkable piece of ignorant, hysterical nonsense. When chlorination was stopped in Peru in 1991 as a result of pressure from the EPA and Greenpeace, an epidemic broke out that spread through Latin America. Some 800,000 people became ill with cholera and 6,000 people died. Millions of people are still dying all over the world because of dirty water.

The anti-chlorine movement was one of the many legacies of Rachel Carson. It was intensified by an EPA study in the mid 1980s that purported to show that one of the by-products of chlorination (trihalomethanes) was carcinogenic. This involved subjecting hapless rodents to very high concentrations.

That was a classical piece of junk epidemiology, based on accidental correlation, of the sort that editors cannot resist. Take just one of the conditions mentioned.

Anencephalus is so rare that most people have never heard of it. Its frequency is less than two per ten thousand of live births, so the impressive number whittles down to something under 80 actual cases. These are then divided into at least two groups - those who are exposed to the putative cause (at an arbitrary threshold) and those who are not. So the whole claim is based on a group of less than 40 babies - unlikely to produce a significant result, even with the debased statistical standards used by modern epidemiology.

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