Five suspects have been detained over a Chinese chemical company's dumping of carcinogenic industrial chemicals that could threaten the water sources for tens of millions of people, police in the southwestern Yunnan Province said Tuesday.

5 detained over toxic waste dumping.[File photo]

The suspects included a deputy general manager and an employee of the Luliang Chemical Industry Co., Ltd., which 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, the public security bureau in Qujing City said in a press release.

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 it could threaten the water sources for tens of millions of residents.

The third suspect was a deputy general manager with Sanli Fuel Co Ltd in Xingyi City of the neighboring Guizhou Province, which was contracted to transport Luliang Chemical's industrial waste to Guizhou according to a deal signed between the two companies, the press release said.

It said police had previously detained two other suspects who dumped the waste near the reservoir instead of trucking it to Guizhou.

Investigators with the Pearl River Water Conservancy Committee said last week they had found excessive cancer-causing hexavalent chromium (chromium VI) at the dumping sites.

The committee said no apparent chromium VI pollution was detected in major drinking water sources, including the Huangnipu Reservoir and the Nanpan River.

The city government of Qujing said last week it would investigate to determine if any watchdog officials were guilty of dereliction of duty in the pollution scandal.

It has also ordered a thorough check on the distribution of all dangerous materials amid efforts to prevent similar pollution threats.

No human deaths have been attributed to the chromium pollution, but at least 14 local residents have been diagnosed with cancer since 2002 and many suspect their diseases were caused by contaminated drinking water.

At least 3,000 people live near the dumping sites.