The United Nations says it could take 30 years to clear up pollution from oil operations in the Ogoniland region of Nigeria.
A report by the UN Environment Programme says oil spills have contaminated land, sea and air, seriously threatening public health in some areas.
Drinking water at least 10 Ogoni communities was contaminated with high levels of hydrocarbons, seriously threatening public health.
In one community, the report says, families were drinking from wells which were contaminated with benzene, a known carcinogen, at 900 times recommended levels.
The report, based on examinations of some 200 locations over 14 months, said multinational oil company Shell had created public health and safety issues by failing to apply its own procedures in the control and maintenance of oilfield infrastructure.
But it also said local people were sabotaging pipelines in order to steal oil.
