Growing pollution poses mounting problems for public health. In virtually all countries studies identify health problems linked to environmental contaminants (31, 129, 130, 132, 142, 145, 151, 194, 197, 203, 206, 253, 272). Such studies have a long history. In 1855 John Snow published the results of his innovative study of the causes of cholera in London, attributing it to drinking water contaminated with raw sewage—marking the beginning of the field of epidemiology (218).

In developing countries today the old killers are still around—tuberculosis, malaria, and diarrheal diseases, among others—and now HIV/AIDS. But joining these as important causes of death and ill health are cancers and chronic diseases caused by industrial and agricultural chemicals and other pollutants in the atmosphere, soil, and water (193).

Lead, mercury, copper, arsenic, and other heavy metals used in industry have caused many deaths. A number of pesticides and other chemicals, known as POPs (persistent organic pollutants), which are used both in agriculture and in industry, can cause cancer and genetic abnormalities in humans.

D. Hinrichsen

Above: In Cairo thousands of cars, trucks, and buses sit in traffic. Below: A pall of pollution hangs over the city of Bogota. In many developing countries, atmospheric pollution is a serious hazard—responsible for at least 2 million deaths annually. Curbing outdoor and indoor air pollution would improve health substantially.

D. Hinrichsen

Air pollution kills an estimated 2.7 million to 3.0 million people every year—about 6% of all deaths annually (171, 227, 261). About 9 deaths in every 10 due to air pollution take place in the developing world, where about 80% of all people live (227) (see Table 1).

About 2.5 billion people, almost all in developing countries, suffer from high levels of indoor air pollution (200). Indoor air pollution is due to burning wood, animal dung, crop residues, and coal for cooking and heating. Most of the victims of indoor pollution are women and girls, who have primary responsibility for cooking and tending the house (227).

Outdoor air pollution harms more than 1.1 billion people, mostly in cities (196). The World Health Organization (WHO) estimates that about 700,000 deaths annually could be prevented in developing countries if three major atmospheric pollutants—carbon monoxide, suspended particulate matter, and lead—were brought down to safer levels (48, 261). The direct health cost of urban air pollution in developing countries was estimated in 1995 at nearly US$100 billion a year. Chronic bronchitis alone accounted for around US$40 billion (227).

In cities that lack pollution controls, millions of people are at risk from outdoor pollution. Densely populated and rapidly growing cities such as Bangkok, Manila, Mexico City, and New Delhi are often entombed in a pall of pollution from trucks and cars and from uncontrolled industrial emissions. In 1995, for example, the average ozone concentration in Mexico City was about 0.15 parts per million, 10 times the natural atmospheric concentration and twice the maximum permitted in Japan or the US (96, 157). Ozone is a powerful secondary pollutant formed when oxides of nitrogen and unburned volatile organic hydrocarbons, mostly from vehicle exhausts, combine with oxygen under the action of sunlight. Ozone is a main component of smog.

Another powerful secondary pollutant is acid rain, formed when sulfur dioxide and oxides of nitrogen combine with water vapor and oxygen in the presence of sunlight to form a diluted "soup" of sulfuric and nitric acids. They can fall as both wet (acid rain) or dry deposition. Other harmful pollutants include sulfur dioxide, suspended particulate matter (soot, ash, and smoke from fires), carbon monoxide from vehicle exhausts, and lead, mainly from the exhaust of vehicles that burn leaded gasoline (262).

Air pollution is not only a health hazard but also reduces food production and timber harvests, because high levels of pollution impair photosynthesis. In Germany, for example, about US$4.7 billion a year in agricultural production is lost to high levels of sulfur, nitrogen oxides, and ozone (227).