Eight people have been arrested over a Chinese company's illegally dumping of carcinogenic industrial chemicals that could pollute the water sources for tens of millions of people in southwestern Yunnan Province's Qujing City, local government officials said Sunday.

Chen Jun, deputy?mayor of Qujing City.

The?eight?suspects include the two workers who dumped the waste, the deputy manager and a worker with the chemical plant, Luliang Chemical Industry Co, and workers with the fuel company who were in charge of waste transportation, Chen Jun, deputy mayor of Qujing City, said at a press briefing.

Luliang Chemical Industry Co., Ltd. was found to have illegally dumped over 5,000 metric tons of chromium-contaminated waste near the Chachong Reservoir and on hills of Qilin District in Qujing from April to June,Xinhua reported.

Rainfall in June washed some of the chemicals into local water supplies and caused 77 cattle to die.

As the Chachong Reservoir and its downstream river feed the Pearl River, one of China's longest waterway, the pollution scandal sparked fears that it could threaten the water sources for tens of millions of residents downstream.

A further investigation by local environment watchdog also revealed that nearly 150,000 metric tons of waste were piled inside the company, which is located by the Nanpan River, raising concerns over the pollution to the river through leakage.

The chemical company was fined 300,000 yuan for damaging the environment and production there has been halted, Chen said.

"The accident shows that the supervision of industrial companies is lacking in the area, while unsound emergency plans failed to inform residents of the current environment condition," Chen said.

Chen promised the Qujing municipal government would complete decontamination treatment of the waste by the end of 2012.

The officials also said they would be developing new technologies to refine chromium material from the waste and have it recycled.

(Shanghai Daily contributed to this story)