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[BEIJING] Some 65 million Chinese rely on underground water supplies that are heavily contaminated with arsenic or fluoride, according to the first national survey of the quality of the country's supply of drinking water.

SciDev.Net has seen an early preview of the summary of the report, whose public release date still needs to be confirmed.

Sixty-three million people drink water contaminated by fluoride, said Wen Donghai, director of the China Geological Survey's hydrogeology division and co-chair of the survey, in an interview with SciDev.Net yesterday (28 April).

In addition, he said groundwater used to supply two million is contaminated by arsenic.

According to Wen, those affected by high levels of arsenic in their drinking water live mainly in northern China's Shanxi Province and the Inner Mongolia Autonomous Region, as well as Xinjiang Autonomous Region in the northwest.

Heavy fluoride pollution in groundwater, on the other hand, is more widely distributed across different regions of China.

Arsenic pollution is mainly due to natural geological conditions, such as the presence of arsenic underground nearby sources of water. Some human activities also lead to arsenic pollution such as burning arsenic-rich coal in the southwestern Chinese provinces of Yunnan and Guizhou.

The smoke frequently contaminates the drinking water and food of local villagers, says Wen.

High levels of arsenic in drinking water can cause high blood pressure, neurological diseases, diabetes and cancer. Excessive fluoride can trigger arthritis and tooth loss.

In recent years, scientists have used plants and microorganisms to remove arsenic from soil. A species of fern called Pteris vittata, for instance, is particularly effective at absorbing arsenic (see Ferns clean up poisoned water).

But Wen says that plants might only be able to do a limited amount of good, when it comes to absorbing arsenic and fluoride pollution in groundwater. This is because their roots don't usually reach the most heavily contaminated layers of the soil.

He recommends a more basic solution to the problem of arsenic pollution — drilling wells below the soil layers that contain arsenic.

Geological surveys suggest that soil and rock layers under the layers containing arsenic are usually free of the contaminant, Wen said.

"If we pump water from the deeper arsenic-free soil layers and build the well walls using cement and PVC [polyvinyl chloride] material to prevent the infiltration of arsenic into the water, people can avoid arsenic pollution in their drinking water," he added.

Wen said the China Geological Survey is planning to launch a programme to detect clean and safe water sources in regions with high-arsenic and high-fluoride groundwater.