We all know what the world's worst industrial disaster was: the gas leak from the Union Carbide factory in Bhopal in central India. On the night of 2 December 1984, the creaky pesticides plant, which was lacking a number of basic safeguards, released a cloud of methyl isocyanate, phosgene and other gases over a densely populated city. This poison gas killed thousands of people – some immediately, many others in the years that followed. The death toll so far appears to be around 25,000. Hundreds of thousands of others were harmed, in many cases permanently. The 25th anniversary falls in just over two months.

I mentioned it in my column last week, in relation to the Trafigura waste dumping scandal. But until I received a letter about it last week, I had no idea just how little had been done to ensure that the remaining poison spread no further. You might have imagined that after the global outrage this disaster caused, and the way in which Bhopal has become shorthand for corporate malfeasance and insouciance, that the site of this great crime would have been cleaned up and sorted out as quickly as possible. That the plant, which was closed after the gas leak, would either have been demolished and removed or cleaned up and turned into a memorial for the victims. You'd be wrong.

As the Bhopal Medical Appeal reminds us, the plant has instead simply been abandoned. Hundreds of tonnes of deadly chemicals have been left there – in open pits or just piled on the ground – to leach into the water supply, where they continue to poison people to this day, causing cancer and foetal malformations, among other horrible effects. The chemicals include deadly pesticides and their even deadlier precursors.

After drinking half a glass of water that the people of the city drink every day, the author Dominique Lapierre reported that "my mouth, my throat, my tongue instantly got on fire, while my arms and legs suffered an immediate skin rash. This was the simple manifestation of what men, women and children have to endure daily, some 18 years after the tragedy." Seven years on, nothing has changed. There has been no cleanup, no attempt to prevent the leakage from the site that takes place during every monsoon.

In 1994, Union Carbide (owned by Dow Chemical since 2001) sold the company's Indian subsidiary, and hence (or so it claims) divested itself of all responsibility for the plant, the disaster and its aftermath. The Indian government also appears to have washed its hands of the plant. The people of Bhopal, who have already suffered so hideously, are being poisoned all over again.

Has nothing been learned? Are Indian lives considered so cheap that even the people of Bhopal, who are owed so much, can be treated like vermin? For how much longer will we stand by and let this horror continue?

www.monbiot.com