BioEd Online

What happened?

In late August, more than 400 tonnes of waste was dumped at more than ten sites across the port city of Abidjan.

Before experts arrived on the scene, seven people had died, although no autopsies have been done to verify the cause of death. Some 40,000 people queued up for free healthcare being offered at local hospitals, complaining of breathing difficulties, nausea, headaches and stomach pains; a UN humanitarian report notes that 24 of these consultations have resulted in further precautionary examinations.

Tredi, a subsidiary of the French firm Sch, is taking on the clean-up operation.

What's in the waste?

Trafigura, a Dutch firm that chartered the ship that was the source of the waste, said that it consisted of washings ('slops') from a cargo of gasoline. UN reports have shown that the waste contains three classes of toxic chemicals: hydrogen sulphide gas (H₂S), which smells of rotten eggs and can kill if inhaled in high concentrations; mercaptans (sulphur-containing petrochemicals); and benzene derivatives including phenols. The rest of the waste is hydrocarbons, as found in petrol, with trace amounts of chlorinated hydrocarbons.

How dangerous is the current situation?

Séché group's international director Michael Smeets says that the immediate danger seems to have passed. Concentrations of hydrogen sulphide gas in the air around the dumps are now at a safe level. And fortunately, most of the dump sites stand on natural clay, which prevents pollutants seeping into groundwater. Only in the lagoon which may have been already polluted is there some question of water pollution; that requires a much longer-term clean-up than the immediate emergency operation.

The UN humanitarian report states that no dead fish have been seen in the lagoon, and vegetables growing on nearby dump sites don't seem to have been touched. Authorities nevertheless plan to destroy these plants to discourage the practice of growing food in garbage areas generally.

How is the waste being removed?

Twenty-five experts are on the site directing the clean-up operation, which began on 17 September. They're using 60 tonnes of equipment flown in from Europe, and hiring bulldozers, diggers and cranes in Abidjan.

"The immediate goal is to stop any further exposure to the population and surroundings," says Smeets. The waste, which looks like black tar, is simply excavated from the grey municipal waste around it, and dumped into containers, or pumped into tanks, under UN supervision. "It's less complicated than we expected: the dumps aren't very high, and the black waste is easily identified," Smeets says.

Staff wear suits and masks, while the air quality is monitored and a back-up medical intervention team stands by. "Even sweeping the soil can be a risky undertaking when dangerous particles are present," says Smeets.

How long will it take to clean up the mess?

Once all the waste is removed, it is stored in containers in a secure site by Abidjan harbour. "We expect this first stage will be achieved within a fortnight," says Smeets. At the same time, small samples are being flown back to laboratories in Europe, to determine exactly what the waste contains.

The waste will then be shipped to treatment facilities in France and Germany, following a maze of safety conventions and logistics that will likely take weeks to navigate. The material will then be treated by the usual protocols for such contaminants: toxic hydrocarbons are incinerated at more than 1,200 °C, which breaks up compounds such as benzene back to carbon dioxide and water; heavy metals are concentrated and mixed with cement to be buried in landfills.

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