Cadmium from a zinc smelter spilled into the Beijiang River in the southern province of Guangdong during repair work on equipment last week.
Cadmium can cause bone diseases and damage the liver and kidney.
As a result of the accident, the 500,000 inhabitants of the city of Shaoguan spent 20 December without drinking water.
Ninety kilometers downstream, Yingde has begun drawing drinking water for its 100,000 residents from a nearby reservoir.
The spill is expected to be diluted by the time it reaches Guangzhou, a city of more than 6.5 million people. Water levels at a dam upriver have already been lowered in an effort to the reduce the concentration of pollutants in the river.
Last month an explosion at a northern chemical factory spilled benzene into the Songhua River. The toxic slick has since reached Russia's Amur River and is expected to reach Khabarovsk today.
A slick of toxic benzene and other chemicals is moving from China's Songhua River toward the Amur River in Russia's Far East. Russian authorities fear the consequences when the 80-kilometer-long toxic slick reaches the city of Khabarovsk, which relies on the Amur for its water supply.
Officials say supplies of clean water and filtering charcoal are being stockpiled in Khabarovsk. Russian authorities have warned that more than 1 million people living along the Amur could be affected by the contaminants. The spill is the result of an explosion on November 13, 2005, at a Chinese chemical plant in the city of Jilin....(more)