One August morning, people living near the Akouedo rubbish dump in Abidjan, capital of the Ivory Coast, woke up to a foul-smelling air. Soon, they began to vomit, children got diarrhoea, and the elderly found it difficult to breathe. "The smell was unbelievable, a cross between rotten eggs and blocked drains," said one Abidjan resident. "After 10 minutes in the thick of it, I felt sick."

As they live near the biggest landfill in Abidjan, the people of Akouedo are used to having rubbish dumped on their doorstep. Trucks unload broken glass, rotting food and used syringes. Children try to make the best of their dismal playground, looking for scraps of metal and old clothes to sell for a few cents.

But this time, the waste would benefit no one. By yesterday, at least six people, including two children, had died from the fumes. Another 15,000have sought treatment for nausea, vomiting and headaches, queuing for hours at hastily set up clinics. Pharmacies have run out of medicines and the World Health Organisation has sent emergency supplies to help the health system. The Ivorian government had resigned over the matter and, so far, eight people have been arrested.

The tragedy is said to have begun on 19 August, after a ship chartered by a Dutch company offloaded 400 tons of gasoline, water and caustic washings used to clean oil drums. The cargo was dumped at Akouedo and at least 10 other sites around the city, including in a channel leading to a lake, roadsides and open grounds.

The liquids began to send up fumes of hydrogen sulphide, petroleum distillates and sodium hydroxides across the city. As the tidy-up operation begins, environmental groups have begun to ask how this occurred.

"We thought the days when companies shipped toxic waste to poor countries were over," said Helen Perivier, toxics co-ordinator for Greenpeace. "It peaked in the 1980s but since then the determination of African countries to stamp the trade out has helped yield results. That this has happened again is extraordinary."

Probo Koala, the ship that offloaded the waste, is registered in Panama and chartered by the Dutch trading company Trafigura Beheer. Trafigura had tried to offload its slops in Amsterdam, but the Amsterdam Port Services recognised its contents as toxic and asked to renegotiate terms. Trafigura said shipping delays would mean penalties of at least 250,000 US dollars (£133,000) so handed it over to a disposal company in Abidjan alongside a "written request that the material should be safely disposed of, according to country laws, and with all the correct documentation."

This story is a common one. All down the West Africa coast, ships registered in America and Europe unload containers filled with old computers, slops, and used medical equipment. Scrap merchants, corrupt politicians and underpaid civil servants take charge of this rubbish and, for a few dollars, will dump them off coastlines and on landfill sites.

Throughout the 1980s, Africa was Europe's most popular dumping ground, with radioactive waste and toxic chemicals foisted on landowners. In 1987 an Italian ship dumped a load ofwaste on Koko Beach, Nigeria. Workers who came into contact with it suffered from chemical burns and partial paralysis, and began to vomit blood.

Thereafter, the UN drew up plans to regulate the trade in hazardous waste through the Basel Convention. By 1998, the European Union had agreed to implement the ban, which prohibited the export of hazardous wastes from developed countries to the developing world, but the USA, Canada, Australia and New Zealand refused to sign up;global waterways are still filled with ships looking to unload their toxic waste.

And now, there is a new threat - the dumping of electronic waste, or e-waste: unwanted mobile phones, computers and printers, which contain cadmium, lead, mercury and other poisons. More than 20 million computers become obsolete in America alone each year.

The UK generates almost 2 million tons of electronic waste. Disposing of this in America and Europe costs money, so many companies sell it to middle merchants, who promise the computers can be reused in Africa, China and India. Each month about 500 container loads, containing about 400,000 unwanted computers, arrive in Nigeria to be processed. But 75 per cent of units shipped to Nigeria cannot be resold. So they sit on landfills, and children scrabble barefoot, looking for scraps of copper wire or nails. And every so often, the plastics are burnt, sending fumes up into the air.

"There is a tradition of burning rubbish all over Africa, but this new burning of electronic equipment is incredibly dangerous," said Sarah Westervelt of the Basel Action Network, a pressure group that monitors the trade in hazardous waste. In China, workers burn PVC-coated wires to get at the copper, and swirl acids in buckets to extract scraps of gold.

The United Nations Environment Programme estimates that worldwide, 20 million to 50 million tons of electronics are discarded each year. Less than 10 per cent gets recycled and half or more ends up overseas. As Western technology becomes cheaper and the latest machine comes to be regarded as a disposable fashion statement, this dumping will only intensify.

"Electronic goods are the fastest growing area of retail," said Liz Parkes, head of waste regulation at the Environment Agency. "We need to encourage people to think about whether they really need a new electronic item, and to consider what happens to the goods they throw out."

Where does our rubbish go?

* Inspections of 18 European ports in 2005 found that 47 per cent of all waste destined for export was in fact illegal. (Greenpeace)

* In 1993, there were two million tons of waste crossing the globe. By 2001, it had risen to 8.5 million. (UN)

* UK households throw away 93 million pieces of electrical equipment a year - about four items per household. Many of these end up in West Africa, India or China. (Industry Council for Electronic Equipment Recycling)

* There are more than 20 million redundant mobile phones in the UK. (Industry Council for Electronic Equipment Recycling)

* From next summer, manufacturers and importers of electrical goods will have to take responsibility for collecting and reusing old or outdated equipment. (Defra)

* It is illegal to ship hazardous waste out of Europe, but old electronic items can be sent to developing countries for "recycling". (Defra)