One of the most worrying features of the problem is that very little is known about the long-term consequences of exposure to hazardous chemicals, although a good deal is known about their short-term effect. It is known, however, that consequences over long periods can include cancer, delayed nervous damage, malformations in unborn children, and mutagenic changes that could produce disability and disease in future generations. The situation is made even more difficult because, once they are in the environment, chemicals spread in a very complex way and may be converted into other substances which have different effects.
Some 90% of hazardous wastes are produced in the industrialized countries. As developing countries industrialize and urbanize they are generating ever greater amounts of dangerous waste. Much of the resultant pollution spreads beyond national borders. In China, India and Thailand, for example, burning low quality coal adds substantially to the global problem of acid rain and greenhouse gases.