Three people responsible for the leaking of poisonous arsenic in southwest China's Guizhou Province have been detained, local police said on Saturday.

Zhang Deren, who started to run a sulphuric acid plant in Dushan County in the Buyi and Miao ethnic autonomous prefecture in southern Guizhou in December last year without the permit of relative authorities, has been detained for the accident.

Zhang's wife Song Rongju, and Song's brother Song Ronggui, who were involved in sulphuric acid production and also held responsible for the chemical spill, were under house arrest and in custody, respectively.

Twelve villagers were slightly poisoned, showing symptoms of nausea, vomit, diarrhoea and headache. Another 21 residents felt uncomfortable and doctors tested excessive amount of arsenic in some of their urine.

All the affected villagers have recovered and released from hospital as of Saturday.

Initial investigation showed that arsenic-containing waste water was leaked from timeworn and substandard production equipment in the plant in early December, but it was still unknown how much arsenic was in it.

The spill slowly reached the downstream Duliu River that runs through Sandu County on December 24, forcing the closure of a water plant which takes water from the river, and leaving some 20,000 residents in drinking water shortage for about ten days.

The local government has been offering bottled water to ensure people's basic need and trying hard to deal with the pollution.

Nearly two tons of carbon and 4,400 tons of calcium oxide have been put into the contaminated river to absorb the poisonous chemical and induce sediment.

The local government has earmarked some 1 million yuan in the drinking water supply and river purification efforts.

The southern part of Guizhou has been suffering from a drought that was rare in 50 years, but it helped to slow the spread of the chemical spill to downstream areas.

In the worst situation, every liter of the river water contained 0.56 mg of arsenic but it dropped to 0.196 mg per liter, still higher than the state standard of 0.05 mg per liter.

However, the river is expected to return to normal in two weeks before it reaches Hunan Province, said Yang Bo, deputy director with environment protection bureau of southern Guizhou, as more rainfall in the downstream regions will help to dilute the pollution.

No contamination has been found in lower reaches of the river so far, according to test results from water quality monitoring stations along the river.

The water plant has upgraded its equipment to ensure the production of safe drinking water. Workers were busying testing all facilities Saturday night for the resumption of operation on Sunday.

Arsenic could be found in human bodies, but excessive amount of the chemical element, especially arsenic trioxide, would cause cancer, poisoning or even death.

(Xinhua News Agency January 6, 2008)