Beijing: China will launch its first nationwide investigation into the sources of environmental pollution which will serve as a reference for the government in tightening 'soft' laws, a top environmental official has said.

"It will take three years to ascertain just how much pollutant is discharged all over the country," director of the State Environmental Protection Administration (SEPA), Zhou Shengxian said, noting that the survey will start in 2008.

A list of products likely to cause heavy pollution is being drafted, Zhou told the first national work conference on environmental policies and the legal system here yesterday.

He said that the list would provide a reference for the government, who will then exclude the items from export rebates, slap higher customs duties on them or impose limits on imports.

He also acknowledged the disadvantages of the current environmental legal and policy system.

"The number of complaints and protests over pollution has been rising at an annual rate of 30 per cent in recent years," he said.

"Pollution problems have undermined social stability in some areas," he said, attributing it mainly to an inadequate legal system and slack law enforcement.

He noted that China's Environmental Protection Law, which has not been amended since 1989, was too 'soft' as fines were too low and local environment departments were not granted enough authority and power.