An official with the Chinese national State Environmental Protection Administration (SEPA) who declined to give his name was quoted by Thursday's China Business News as saying that the allegation is "entirely groundless".

The British newspaper, Financial Times, on April 12 cited U.S. Environmental Protection Agency (EPA) chief Stephen Johnson as saying that "China's airborne chemicals and particulate matter were being detected on both coasts of the U.S.."

Zhang Jianyu, program manager for the Beijing office of Environmental Defense, a US-based non-governmental organization, said, "As far as I know, Stephen Johnson has never made this kind of claim publicly."

"It's impossible to distinguish the origin of pollutants in the global atmosphere," Zhang noted.

The allegation was not news to the Chinese, according to Zhang.

Based on his researches to determine if China's airborne pollutants could travel to the United States, Prof. Daniel Jacob of Harvard University claimed in 2004 that imported pollution could degrade the atmosphere in the U.S., Zhang said.

"The claim, however, is only conjecture," the newspaper cited Zhang as saying. "It is not a foregone conclusion yet."

Mercury is a highly-toxic heavy metal that does harm to the human nervous system. When it settles on land or lakes it can be ingested by animals that then flow into the human food chain.