Hidden operation

Another of the responsible factories, Hongquan Lithopone Materials Plant in Hechi, about 14.5 km upstream of Lalang hydropower station, was accused of illegal production and dumping waste directly into the river.

Local authorities approved the plant in 2007 to produce lithopone, a widely used white paint pigment, and zinc sulfide. However, it has been producing the metal indium, outside its business scope, since December 2009.

Guangxi's environmental protection bureau said the company made careful arrangements to hide its illegal operation: The key production unit is locked down so no outsiders can approach. The products are packed in bags without clear labels. Except for key management and technical staff, most workers at the plant don't know what they are actually producing.

Worse, the bureau said, the company has no pollution treatment facilities. All sewage, with a high concentration of heavy metals, is stored temporarily in 10 tanks. The waste contains highly toxic cadmium, arsenic and zinc, and it is discharged into nearby underground caves through well-covered channels.

The names of the five other responsible operations were not disclosed. Nine executives at Jinhe and Hongquan have been detained.

But the environmental authorities did not say what triggered the major chemical spill this time. The illegal dumping of wastes at the two plants has been going on for quite a while.

These cadmium bricks at Jinhe weigh a ton. Jiang Dong / China Daily