Leaded gasoline causes about 90 per cent of airborne lead pollution in cities, the rest of which comes from factories, power plants, lead pipes, lead-based solder and paint. In the developing countries, about 15 million children may be suffering from permanent brain damage due to lead poisoning. About 80 per cent of children aged between three and five living in urban areas have blood lead levels which exceed the health standards set by the World Health Organization. Exposure to lead, particularly in children under six, frequently causes learning disabilities, hearing loss, reduced attention span, behavioural abnormalities and a drop in iq..