Commentary: Assessing the effects of environmental pollution when people know that they have been exposed

Acute episodes of massive air pollution with harmful effects are fortunately rare, but this means that no one is very experienced at investigating such risks. The immediate effects may be blast and burns injuries, acute chemical toxicity as at Bhopal in 1984, irritation causing acute respiratory and conjunctival symptoms, or the sight and smell of smoke and fumes causing fear. The suddenness and speed at which the pollution arises, usually in an explosion or a fire, give little chance of collecting data before exposure. Epidemiological studies into the longer term effects have to be done after the pollution has dispersed and when public opinion has formed about the …