WASHINGTON -- Raw coal laced with arsenic, fluorine lead and mercury is threatening the health of millions of Chinese who use it as fuel for heating and cooking, a new study shows.

The study, published Tuesday in the Proceedings of the National Academy of Sciences, found that the poison contaminants become part of the smoke from burning the raw coal and are then breathed into lungs and baked into foods, said Harvey E. Belkin, co-author of the study.For example, peppers dried over coal fires can have up to 500 parts per million of arsenic, a potentially dangerous level, said Belkin.

An estimated 800 million of China's 1.2 billion people use coal in their homes, said Belkin, and much of the fuel contains dangerous contaminants.

In one Chinese province, experts have identified thousands of cases of arsenic poisoning, with symptoms including skin cancer and open sores.

In another area, at least 10 million people have fluorine poisoning with many suffering from soft and misshapen bones, said study co-author Robert B. Finkelman.

Diseases and disorders caused by burning of dirty coal are "an enormous problem," said Finkelman.

Such dirty coal would have to be cleaned before it could be burned in the United States, said Belkin. And coal in any form is seldom used in the United States for cooking.

In China, he said, about 22 percent of rural homes depend on coal for domestic fuel.

"If they want to cook or heat, they have to use coal," he said. China has very little oil, gas or wood that can be used for fuel. But China has the world's largest known reserves of coal. For many peasants, the coal is dug out of hillsides, free for the taking.