JINAN, Feb. 3 -- A total of 25 people including bosses of five chemical companies in east China's Shandong Province have been detained for illegal discharge of dangerous chemicals which led to the death of four people, police said on Wednesday.

On Oct. 21 last year, four bodies were found in Shanggao Village, Zhangqiu City. Police smelled suspicious odor at the scene and discovered lye being illegally discharged into an abandoned mine nearby, said Hou Lei, an investigating officer.

The waste originated with Shandong Jincheng Zhongyou, a chemical company in Zibo City. The four victims had been hired by the company to discharge the toxic waste illegally at a low cost, Hou said, and died as a result of inhaling toxic fumes.

Investigators found another four companies in the province whom they suspected of also illegal discharge of toxic waste.

"To avoid costs between 3,000 (about 450 U.S.dollars) and 6,000 yuan per tonne, the companies hired people to dispose of the waste at a cost of around 300 yuan per tonne," Hou said.

Those who lost their lives in the illegal business only earned about 100 yuan per tonne, but caused severe damage to the environment, Hou said.

A total of 25 suspects have been detained so far, including 12 arrested.