Environmental protection officials said on Sunday that the pollution caused by cinnamene that leaked into the Hanjiang River after a traffic accident early on Saturday is under control.
Pang Tao, deputy director of the provincial environmental protection department's emergency office, told China Daily that about 7 tons of the chemical leaked into the Hanjiang River, the second-largest tributary of the Yangtze River, the longest river in China.
Based on hourly testing of water samples taken from the river, the toxic chemical was found to have polluted a 5.5-km stretch of the waterway, less than expected, he said.
A tanker carrying more than 30 tons of cinnamene was en route from Northwest China's Shaanxi province to neighboring Sichuan province when it overturned on a national highway in Ningqiang county of Shaanxi province at 3 am on Saturday.
Local authorities evacuated more than 400 villagers and blocked the highway, because cinnamene is explosive.
Cinnamene is a toxic chemical used to produce synthetic rubber and plastic. It pollutes soil, water and air.
People exposed to it will feel a sting in the eyes and upper respiratory tract. They may also develop a headache or vomit.
Three cofferdams were put up by the county government to minimize pollution downstream on the Hanjiang River.
Cofferdams are temporary watertight barriers that allow an area to be pumped dry.
"The situation is under control now. With the natural evaporation of cinnamene and other measures, the stretch of polluted water will be further reduced in the coming days," he said.
"We will continue the hourly testing of water samples until no trace of the chemical is found," he said.
The highway reopened on Saturday afternoon after the damaged tanker was towed away, along with the remaining chemical.
"The villagers all returned by Saturday afternoon, after we were told by the environmental protection department that the leak's impact is limited," said Wang Xingcheng, a publicity official with the Ningqiang county government.
He denied reports that the leak had polluted the drinking water of nearly 200,000 people who live downstream from the accident.
"This section of the Hanjiang River has been rather dirty, so people have not taken drinking water from the river for a long time. Villagers' drinking water comes from the Hanjiang River's tributaries," he said.
But the government still warned people not to drink or use water from the river, "just in case", he added.
"Now the river is full of stalks and active carbon, which are used for adsorption of the chemical," he said.
Pang, who was at the scene to inspect the local government's handling of the accident, said that there was no strange odor near the river on Sunday.
But the soil at the site still smells, and professionals were treating it on Sunday afternoon, he said.
An investigation into the cause of the accident is under way.
Wang said local traffic police have not reached any final conclusion about the accident yet. But as the accident happened at 3 am, it is likely to have been a case of driver fatigue, he said.
Xinhua News Agency reported that the driver and another person in the vehicle were slightly injured.