An explosion at a petrochemical plant upstream of Harbin city in northeast China has caused major pollution of the Songhua River with toxic chemicals including benzene, Chinese officials say.
Harbin, one of China's biggest cities with nine million people, draws its drinking water from the river.
Here are some facts on benzene:
Benzene is a clear, colourless, volatile liquid derived from petroleum, with a characteristic sweet "aromatic" smell.
Breathing very high levels can result in death, while high levels can cause drowsiness, dizziness, rapid heart rate, headaches, tremors, confusion and unconsciousness. Eating or drinking foods containing high levels of benzene can cause vomiting, dizziness, sleepiness, convulsions, rapid heart rate and death.
Benzene is used in small
quantities in petrol
It should only be handled with protective clothing, including a chemical hood, goggles and gloves.
First aid measures include flushing eyes and skin with copious amounts of water and removing contaminated clothing.
Benzene has been found to cause cancer in laboratory animals, and it is classed as a human carcinogen by the US and UK governments.
It is a basic chemical used as a building block in the petrochemical industry to produce a wide range of everyday products such as paints, dyes, packaging, adhesives and compact discs.
Benzene is used in small quantities in petrol and other fuels to improve the octane rating but its presence is being minimised.
Information from Shell Chemicals, US government, Wikipedia and water purity Web sites