When Hou Jiwen was born 52 years ago in Hehua Village in southwest China’s Guizhou Province, his house, like many, had a coal-fired clay stove for cooking.

The family used it for baking corn and peppers. Nobody gave the stove a second thought, but even then, it was changing the course of Hou’s life. He didn’t feel anything, although he did notice that his teeth were yellow.

It was only after he married in his 20s and had a son that the stove’s poisoned legacy became apparent.

Hou’s waist and legs began to ache. The bones of his legs became crooked, and he could hardly stand.

Hou had contracted fluorosis, which is endemic in 13 provinces and municipalities where about 33.2 million people live, said Bai Huqun, vice director of the disease control bureau under the Health Ministry.

Guizhou has had the most fluorosis patients. In that province alone, the illness prevails in 35 counties, where nearly 10 million people have dental fluorosis and 1 million have deformed bones due to fluorosis, like Hou.

Despairing of their poverty, his wife left the family 18 years ago, followed by his son, who went away to work in 2004 at the age of 15 and never came back.

Hou lives on a government subsidy of about 17 yuan a month (2.50 U.S. dollars) and grows vegetables on a tiny plot of land. He uses a wooden stick to walk, and sometimes he’s feeling well enough to tend his little farm. Often, his neighbors have to help him.

According to local health authorities, Hou’s illness resulted from the cooking range. In Guizhou, where about 57 percent of the rural households use coal as their major cooking fuel, the coal has a high fluorine content.

Fluorosis has been a problem for humans for ages. Scientists have found it in fossilized skeletons from 200,000 years ago.

Since most clay stoves in southwest China don’t have chimneys, there’s no way for the fluorine to disperse. It’s concentrated in the smoke from cooking, so people breathe it, and it pollutes what’s cooked in the stove. said Deng Tao, vice head of the Health Bureau of Bijie area.

The national standard for fluorine in food is less than 2 milligrams per kilogram, and the standard for indoor density of the chemical in the air is less than 0.007 milligrams per cubic meter. In Guizhou, however, the numbers could be dozens or even hundreds of times higher, Deng noted.

Guizhou started a “stove revolution” in 2004. As of the end of 2008, 82,000 households in the Bijie area of Guizhou had new stoves and another 272,000 had their stoves upgraded.

The new stoves pipe the smoke out of the room.

Yang Shunzhou, a 52-year-old farmer from Luozhuang Village in Dafang County, changed his stove this year.

“My arms have ached for more than ten years and I took for granted that it was rheumatism,” he said. “I didn’t know that we could be poisoned by the cooking range.”

Pointing at the new iron stove, Yang told a Xinhua reporter that it cost 500 yuan, but 300 yuan was paid by the government.

“Now we won’t be sickened anymore,” he said.

The new stoves were not well accepted in some areas at first, said Lin Zhong, head of the health bureau of Dafang County, where as many as 10 percent of the farmers were reduced to poverty due to fluorosis.

Farmers complained that the new stoves, distributed by the government, were of poor quality. Some were used only for a year before the farmers changed back their traditional ranges.

To educate farmers, Guizhou started teaching primary and junior middle students about the fluorosis problem last year.

“Students can influence their parents, to tell them the harm of traditional cooking ranges and ask them to get new ones,” said Wang Jianfu, head of the health department of Guizhou Province.

“If people realize that the traditional ranges mean their teeth will become yellow, their spine will twist, their waist will ache and their legs will be deformed, they will change,” he said

Local governments stopped giving farmers stoves last year and instead encouraged them to buy new stoves on their own, using government subsidies.

Last Thursday, the Health Ministry launched a project to curb fluorosis in six provinces, like Yunnan and Guizhou. This year, it will upgrade the stoves of 870,000 households, with each getting 400 yuan in compensation.

In Guizhou, the government plans to upgrade stoves in 250,000 homes this year. By 2011, it aims to have new stoves in 90 percent of the homes.