The chemical plants being held responsible for polluting the Xinqiang River in central China's Hunan Province with arsenide have been closed and their senior managers detained, China's top environment watchdog said Monday.

Haoyuan Chemical Company, a sulphuric acid manufacturer in Hunan's Linxiang City and Taolin Lead-Zinc Ore Chemical Plant, both in the upper reaches of the river, were the major polluters, said an official with the State Environmental Protection Administration (SEPA).

The two companies had not passed any environmental assessments and had no pollution treatment facilities. They'd been discharging waste water with arsenide content more than 1,000 times higher than the national standard directly into the Xinqiang River for some time, said the official.

Haoyuan Chemical Company discharged nearly 50,000 tons of waste water every month and Taolin Lead-Zinc Ore Chemical Plant 280 tons, he said. However, he didn't reveal over what period of time this had been going on.

Pan Yue, SEPA's deputy director, promised harsh penalties for the enterprises and the top managers may face criminal proceedings.

Xinqiang River, a tributary of China's second largest freshwater lake, Dongting Lake, was found to be polluted last Friday when workers from the county's environmental monitoring center conducted routine testing of water quality and found the content of arsenide was 10 times higher than normal standards.

No casualties have been reported from the contamination. Dongting Lake has tested clear of pollution and the quality of the lake's water running into the Yangtze River is also safe.

Arsenic trioxide is a highly toxic white, powdery substance that can cause vomiting, stomach pains and convulsions. It can lead to those affected going into coma and it can kill. A chronic intake of arsenide could cause liver and kidney damage or lung and skin cancer.

(Xinhua News Agency September 12, 2006)