Courts across south China's Guangxi Zhuang Autonomous Region on Tuesday jailed 13 people in a case involving heavy metal pollution in a river in the region last year.

Three of the jailed were environmental inspectors, who failed to perform their duties and allowed plants to dodge pollution inspections and discharge industrial effluents containing cadmium into the Longjiang River from April 2011, the courts said.

The Dahua County court in Hechi City sentenced Zeng Juefa, fomer vice director of the city's environmental protection bureau, to four and a half years in prison for delinquency and taking bribes.

Lan Qunfeng and Wei Yi, former heads of a district environmental inspection team under the environmental protection bureau of Jinchengjiang District, Hechi City, were each handed jail terms of three years and six months for the same charges as Zeng, as ruled by the Liubei district court of Liuzhou City.

It was also confirmed that Zeng took bribes worth 45,000 yuan (7,335 U.S. dollars) while Lan and Wei accepted bribes -- 20,000 yuan in each case -- the courts said. No briber was specified.

Guangxi Jinhe Mining Co. Ltd. was found to be a polluter and was fined 1 million yuan, as ruled by Jinchengjiang District court in Hechi. The company's three managers were each sentenced to three years in jail, suspended in two of the cases.

Seven managers of another polluter, Hongquan Lithophone Material Co., Ltd., were also sentenced to three to five years in jail.

The pollution was not discovered until January 2012, when dead fish were found near the Lalang Power Station along the river. Investigators found that cadmium concentrations in the river near the power station were 80 times the official standard.

Cadmium is a carcinogenic industrial chemical. The pollution threatened the drinking water source of the downstream Liuzhou City, which is home to 1.5 million people, and it took one month of emergency treatment to restore water quality in the river.