About 70,000 chemicals are on the market, with around 1,500 new ones appearing annually. At least 30,000 are thought never to have been comprehensively tested for their possible risks to people.

　　At first glance, the plastic buckets stacked in the corner of the environmental NGO office look like any others. But the containers are an unlikely weapon in one poor community's fight against oil companies which they say are responsible for widespread ill-health caused by years of pollution. The vessels are used by a network of local volunteers, known as the Bucket Brigade, to gather air samples in neighborhoods bordering oil refineries, as part of a campaign to monitor and document air pollution which they believe is coming from the plants.

　　In South Africa, as in many developing and newly industrialized countries, legislation on air pollution has failed to keep pace with mushrooming industries. So local residents, like many in poor communities around the globe, have faced the problem of investigating their claim that industries on their doorsteps are making them sick.

　　Trade-off

　　But the snag is that modern society demands many of them, and some are essential for survival. So while we invoke the precautionary principle, which always recommends erring on the side of caution, we have to recognize there will be trade-offs to be made.

　　The pesticide DDT does great damage to wildlife and can affect the human nervous system, but can also be effective against malaria (疟疾). Where does the priority lie?

　　The industrialized world has not yet cleaned up the mess it created, but it is reaping the benefits of the pollution it has caused. It can hardly tell the developing countries that they have no right to follow suit.

　　Another complication in tackling pollution is that it does not respect political frontiers. There is a U.N. convention on trans-boundary air pollution, but that cannot cover every problem that can arise between neighbors, or between states which do not share a border. Perhaps the best example is climate change-the countries of the world share one atmosphere, and what one does can affect everyone.