The emergency cleanup of cadmium pollution in South China's Longjiang River will run till the end of February, experts handling the incident said Thursday.

The concentration of cadmium is expected to drop below the official limit on Feb 28, said Xu Zhencheng, head of an expert panel from an emergency center set up to handle the incident.

Cleanup procedures had brought the cadmium concentration peak down from 80 times the official limit to 20 times the limit on Thursday, said Zhang Xiaojian, an expert with the center and a professor of Tsinghua University.

The PH value will be controlled to within 8.5, so no fish will die because of the cleanup work, he said.

It would take several more days for the pollution to arrive in the downstream Liujiang River, Zhang said.

A 300-km section of the Liujiang River, which runs through Guangxi Zhuang autonomous region, will be affected by the cadmium spill.

As of 6 am Tuesday, drinking water produced by four major water plants in Liuzhou was up to standard, with cadmium concentrations no higher than 0.00065 milligrams per liter, according to the latest water quality tests.

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

The contamination was first detected on Jan 15. A plant belonging to Jinhe Mining Co Ltd is one of the suspected sources of the pollution.

Nine chemical plant executives have been detained in response to the incident after one more was detained Thursday afternoon, said a spokesman of Hechi municipal government.

Cadmium is a carcinogenic chemical mostly found in industrial effluents.