Burning issue of a killer profit

December 2002 saw the 50th anniversary of the great killer fog of London that killed 4,000 people in one week. The event was the result of the burning of cheap coal combined with particular weather conditions.

According to Devra Davis, the true mortality was much higher, about 13,000.

She and Michelle Bell showed that death rates were higher in the months between December 1952 and March 1953; earlier reports had attributed these deaths to influenza.

It was not the first of such episodes in London - the adverse effects of air pollution were described centuries ago. In a 1604 pamphlet Counterblaste to Tobacco , King James I warned against "the vile custom of tobacco-taking" and "coal-besotted kitchens". The English diarist John Evelyn, one of the founder members of the Royal Society, added fuel to the campaign against coal smoke. In 1661, he wrote what he called an "invective on coal-burning" in a classic work, Fumifugium , or The Inconvenience of the Aer and the Smoak of London Dissipated . Fumifugium included several remedies such as planting flowers, establishing parks and banishing smoky trades to the outskirts of London. Although the parks idea took root, many of the other ideas did not. Not until 1961 was coal-burning forbidden by the Clean Air Act, by which time pollution levels were already declining.

Davis, born in Donora, a steel-working and zinc-smelting town in Pennsylvania, grew up with air pollution and its effects. Donora suffered an air-pollution episode in 1948: although the cause of the dozens of deaths was probably fluoride poisoning from the zinc works. The combination of a strong pollution source and weather played an important role. Little was initially done to find the cause or to reduce pollution by local authorities or industry because of possible economic consequences for the town. Davis, an environmental epidemiologist who has worked for the US Environmental Protection Agency (EPA) and the Clinton administration, provides interesting and well-described accounts of the events.

Environmental epidemiology, which assesses the relationship between environmental pollution and human disease and mortality, is a relatively new discipline. The strong effects of pollution episodes are relatively easy to detect, but weaker associations between pollution and disease are more elusive if no less important, especially as they may involve a larger number of people than the initial pollution event.

The interpretation of epidemiological studies is made harder by the possibility of bias, chance and intrinsic difficulties in the assessment of pollution, a theme that reoccurs throughout the book. Generally, only a range of studies with consistent results, together with data from animal studies, may force action such as legislation aimed at reducing or eliminating pollution.

An example of both failure and triumph in public health is lead in petrol.

The Ethyl Corporation was launched in 1923 to promote and produce (tetraethyl) lead as an additive to petrol to stop the knocking sound in car engines. Lead was already a well-known neurotoxin and public-health scientists argued against it in petrol. But its use grew dramatically. It took until 1979 for public opinion to turn against lead, when Herbert Needleman found an association between lead in teeth and lower IQ in children, while other studies found other deleterious effects.

In other cases, the evidence is less clear and little action has been taken. Davis describes rises in breast and testicular cancer, hypospadias (a congenital malformation of the penis), cryptorchidism (undescended testicles) and low sperm counts, and rising environmental concentrations of dioxins, polychlorinated biphenyls (PCBs), pthalates, some pesticides and other so-called endocrine-disrupting substances but if there is a link between them, it is still being studied.

In contrast, chlorofluorocarbons (CFC), used as coolants in refrigerators, demanded and received faster action. In 1974, Sherwood Rowland and Mario Molina reasoned that these widely distributed compounds would directly attack the ozone layer, for which they were awarded the Nobel prize for chemistry in 1995. A depleted ozone layer may lead to large increases in skin cancer, cataracts and immune disease. In 1984, a British team measured a "hole" above the south pole. In 1987, the Vienna Convention was signed to take appropriate measures to protect the ozone layer, followed by the Montreal Protocol in 1987, with a specific timetable to phase out the production of CFCs. Cost-benefit studies by the EPA showed that more expensive substitute chemicals would cost 400 times less than not stopping ozone depletion.

This story of how governments finally took action to get rid of CFCs provides important lessons. Three things were required. First, the discovery of the ozone hole provided proof that the planet faced a grave and imminent danger; second, industry found a way to profit from making major changes in the production of the source of the danger; and third, governments saw that the price of doing nothing would be much heavier than the costs of acting.

Davis has worked in many of the areas she discusses, and her book mixes personal, family and work experience. At times, she is selective in her choice of evidence and the reader may require further background reading.

Nevertheless, she provides a fascinating account of the continuing battle between the demands of public health and commercial profit.

Mark J. Nieuwenhuijsen is reader in environmental epidemiology, Imperial College London.