People in the Indian city of Bhopal have been marking 25 years since a leak at a gas plant killed thousands and left many more seriously ill.

印度城市博帕尔的居民纪念导致数千人死亡和更多人重伤的毒气泄漏事件。

Protesters are demanding action to clean up Bhopal site.

Activists¹ and survivors² marched through the city, chanting slogans（标语，口号） against the government and Union Carbide - the US firm that owned the plant at the time.

The incident was the worst industrial disaster in history.

Forty tonnes of a toxin³（毒素，毒质） called methyl isocyanate（异氰酸甲酯） leaked from the factory and settled over slums on 3 December 1984.

Campaigners say at least 15,000 were killed within days and that the effects of the gas continue to this day.

The site of the former pesticide⁴（杀虫剂） plant is now abandoned. The state government of Madhya Pradesh took it over in 1998, but environmentalists say poison is still found there.

Toxin fears

Residents of the city have held a week of commemoration（纪念） events in the lead-up to the anniversary.

Early on Thursday, protesters marched to the site chanting: "Down with the government", and "Down with Union Carbide".

One victim who joined the march told Reuters news agency: "Punish the guilty and remove the toxic⁵ waste from the plant that still contaminates（弄脏，污染） the soil and groundwater."

The BBC took a sample of water from a hand pump in constant use just north of the plant and had it tested in the UK.

It contained nearly 1,000 times the World Health Organization's recommended maximum amount of carbon tetrachloride（四氯化碳）, a pollutant⁶ known to cause cancer and liver damage.

The state government of Madhya Pradesh is now responsible for the site and earlier this week Chief Minister Shivraj Singh Chouhan told the BBC that the water supply around the plant was safe.

On Wednesday, Indian Prime Minister Manmohan Singh said: "The enormity（暴行） of that tragedy of neglect still gnaws⁷ at our collective conscience."

He reaffirmed his government's "commitment to resolving issues of safe drinking water, expeditious⁸（迅速的，敏捷的） clean-up of the site, continuation of medical research, and any other outstanding issues connected with the Bhopal gas tragedy".

Campaigners say Bhopal has an unusually high incidence of children with birth defects（缺陷，瑕疵） and growth deficiency, as well as cancers, diabetes⁹（糖尿病） and other chronic¹⁰ illnesses（慢性病）.

This is seen not only among survivors of the gas leak but among generations born much later, they say.

No-one has ever stood trial over what happened at Bhopal.

Twenty years ago, Union Carbide paid $470m (£282m) in compensation（赔偿，补偿） to the Indian government.

Dow Chemicals, which bought the company in 1999, says this settlement resolved all existing and future claims against the company.