LIUZHOU - A 300-km section of river will be affected by cadmium pollution stretching across 100km of a river in south China's Guangxi Zhuang autonomous region, experts handling the incident said Tuesday.

The river section from the Honghua hydropower station to further downstream of the Liujiang River, which is located downstream of the Longjiang River where the spill occurred, will be affected, said Xu Zhencheng, head of the expert panel with the emergency center set up to handle the incident.

"The cadmium concentration in this section will see an obvious increase, but it will still be within the official limit," Xu added.

The Honghua hydropower station has stored 500 million cubic meters of water, which can greatly dilute the cadmium concentration. Therefore, the cadmium level will be normal downstream of the hydropower station, Xu said.

The pollution belt has brought concentrations of cadmium to more than five times the official limit of 0.005 milligrams per liter.

Cleanup measures, including dumping neutralizers made from dissolved aluminum chloride, brought the cadmium concentration peak down from 80 times the official limit to 25 times the limit on Monday. The current peak is near the Luodong hydropower station on the Longjiang River in the city of Yizhou, according to the center.

All seven of the heavy metal production plants located upstream have suspended operations in order to curb potential sources of new pollution.

The contamination was first detected on January 15, and Jinhe Mining Co Ltd is among the main suspected sources of the pollutant, as its dumping site is not up to national standards.

Seven chemical plant executives have been detained on suspicion of industrial waste discharges, the center spokesman Feng Zhennian said at a press briefing Monday evening.

Cadmium is a carcinogenic chemical mostly found in industrial effluents.

The Longjiang River is an upstream tributary of the Liujiang River, which runs through Liuzhou, a city with 1.5 million permanent residents in the city proper.