BEIJING - Cao Xiaoying, a mother of four children who are all suffering from excessive lead in their blood, looks worried as the smoke rises from chimneys in nearby factories.

Her children are among the hundreds of children with lead poisoning caused by the pollution of the factories in Central China's Hunan province.

The chimneys in the eight smelting firms around Cao's Jinjiling village of Jiahe county are releasing sulfur dioxide, a major contributor to acid rain, which pollutes the air as well as the land with excessive lead levels.