Measures used to bring down cadmium concentration levels following a toxic spill in a Guangxi Zhuang Autonomous Region river are safe and effective, experts said.

By yesterday morning, the water quality in the Liujiang River, a source of drinking water for residents, met national standards, according to data released by the emergency headquarters handling the incident.

Neutralizers designed to gather the matter and ease its removal have been placed in the waterway, and agents designed for dilution in water discharged from upriver dams, said Xu Zhencheng, deputy chief of the South China Institute of Environmental Sciences under the Ministry of the Environmental Protection.

The neutralizers, mainly caustic soda, lime and aluminum chloride, will help increase the PH value and form precipitation compounds such as cadmium carbonate and cadmium hydroxide.

Xu said cleanup procedures organized by the team of more than 100 environmental and water experts had brought peak cadmium concentrations down from 80 times the official limit to less than 20 times the limit.

Cadmium pollution was first detected in the Longjiang River on January 15 in Hechi City. The pollution later spread to the downstream Liujiang River, threatening water security in Liuzhou City, which has a population of 1.5 million.

Police officers have been mobilized to join the cleanup work and ongoing efforts are expected to run until the end of this month.

Professor Zhang Xiaojian, a team member from Tsinghua University, said the neutralizers used are harmless to human health. They include common compounds used for water purification.

Experts said the amount of neutralizers to be dumped depends on the cadmium level.