Nigeria, Benin, Togo, Ghana, and Côte d'Ivoire have decided to ban fuel coming from Europe after campaign group Public Eye issued a damning report which said that European trading firms have been exploiting weak regulations in west Africa to export fuels with levels of sulphur up to 300 times higher than those permitted in Europe.
The Dirty Diesel report highlight the pivotal role played by Swiss commodity trading companies in Africa's fuel industry. On land or at sea, they mix a petrochemical cocktail from refinery products and other components known in the industry as "African quality".
"It increases the amount of sulphur dioxyde produced, so sulphur in fuel directly transforms but it also has a corrosive effect on cars and especially on the emission control technology in cars," Valentino Viredaz, one the report's authors, told RFI. "It will then increase the overall amount of air pollution, in terms of particulate matter, but also nitrogen oxide and many other pollutants."
"Also this "African quality" fuel not only has a high sulphur content but also toxic substances such as benzene and polycyclical aromatic hydrocarbons, all substances that are shown to be very toxic for humans".
The group's analysis revealed the diesel samples contained up to 378 times more sulphur than is permitted in Europe.
After a summit with the United Nations Environment Programme (Unep) the five countries decided to limit sulphur in fuels from 3,000 parts per million to 50 parts per million, 60 times less.
This means that these countries will have to adopt stricter rules when it comes to what they import.
Nigeria's example crucial
"Our standard organisations that regulate the importation of some of these fuels are basically not doing their work," Adetunji Babatunde, from the University of Ibadan in Nigeria, told RFI.
"In the case of Nigeria, we have the Department of Petroleum Resources that should check the quality of some of the imported fuels. And that shows they haven't done so".
Babatunde said this will force Nigeria to upgrade its standards and move towards cleaner energy, meaning Nigeria has to improve its own public and private refineries to meet the same higher standards by 2020.
"Over the half of the diesel consumed in west Africa is consumed by Nigeria. For us, it's very significant that Nigeria made that move," Jane Akumu, from Unep, comments.
"Now it will be easier for the other countries to follow. West Africa is sending a strong message that it is no longer accepting dirty fuels from Europe".
By taking such measures, Nigeria will set an important example in the region, she says.
Companies will go unpunished
Despite the results, Viredaz from Public Eye said it was unlikely the companies exporting "African quality" fuel will be held accountable.
Because, while it's toxic, it's not illegal.
"They're adapting their behaviour to the laws in place in those countries," he pointed out. "They're providing fuel that conforms to what the country asks for. So there's absolutely nothing illegal there".
So the only way to stop the trade is to einforce stricter rules and have them comply with the UN's Guiding Principles on Business and Human Rights adopted in 2011.