Tens of millions of mainland Chinese are being poisoned by unsafe levels of fluoride and arsenic in drinking water, despite decades of official efforts to improve supplies, state media say.

Elevated fluoride levels were found in the water in more than 1,000 counties across the country at the end of 2013, Oriental Outlook, a magazine affiliated with Xinhua, on Monday quoted a Centre for Disease Control and Prevention expert as saying.

Nearly 21 million people suffered diseases caused by excessive exposure, such as skeletal fluorosis – a painful condition that affects bones and joints and which can cripple in severe cases, according to Gao Yanhui, an expert at the centre’s National Centre for Endemic Disease Control. Gao said 87 million people were at risk nationwide.

The worst-hit areas were in the northern plains, with Henan province the most acutely affected, Gao said.

Arsenic poisoning was another concern, with about 600,000 people in 131 counties in about half of the mainland’s provinces affected, the report said. Long-term exposure can cause skin problems and lung, bladder, skin and kidney cancer.

Excessive iodine intake due to poor drinking water had put 30 million people at risk of goitre, a figure little changed from a decade ago, when nationwide research put the number at 30.98 million.

The central government had spent hundreds of billions of yuan over the past decade on improving drinking water in rural areas, but local governments were still short of funds to continue the work, the report said.

It pointed to a project to improve well water in Qianan county in Jilin province. A third of the 590,000 yuan (HK$746,000) spent so far had come from the central government, it cited a project management report as saying. Provincial authorities came up with about 37 per cent, while the public covered the remainder.

“The serious endemic areas are mostly poverty-stricken areas, where local governments are unable to carry out [work on] prevention and control of endemic diseases,” Gao said.

“They can only rely on funds from higher levels [of government] for water improvement projects” and the residents were too poor to come up with the financing themselves, Gao said.

Another expert in endemic-disease control said water-quality projects often involved a range of government departments, which made efficient management more difficult.

Under the existing system, health authorities cannot take the initiative in the projects, while the Ministry of Water Resources – which is responsible for site selection and construction of the projects – lacked geological expertise.

“The water resources departments do not have a grasp of the quality of water, and the wells they drill are often substandard,” he was quoted as saying.

The report did not specify concentration levels for either fluoride or arsenic, but the national standard for fluoride in large-scale centralised supplies is 1mg per litre. The level recommended by the World Health Organisation is 1.5mg/litre.