Toxic winds: PCBs from West Africa overwhelm the Atlantic

Paper Cruising for PCBs

Two research cruises off the west coast of Africa in 2001 and 2005 measured surprisingly high levels of airborne PCBs, far greater than expected. The highest levels coincided with easterly winds blowing from the African coast into the sea, suggesting that they originated from land, but these observations were without precedent in this area, so no firm conclusion could be drawn.

The problem with PCBs, known chemically as polychlorinated biphenyls, is that they are one of the set of ubiquitous persistent organic pollutants (POPs) that the international community is trying to eradicate. The first stage was to ban the production of PCBs, which is having an effect, with ambient European levels on a slow but steady decline.

However, their chemical stability and susceptibility to airborne transport have ensured that they are found in most regions of the globe, including the Arctic. Coupled with the fact that PCBs cause cancer in animals, are probably carcinogenic in humans, and may also have adverse reproductive, developmental, and endocrine effects, this is an unwelcome scenario.

Consequently, the discovery of high PCB concentrations off Africa rang alarm bells. Two sets of measurements four years apart did not suggest an anomaly, so the research team set sail again in 2007 on a cruise from Germany to South Africa. This time, they measured PCBs down the coast, from 25 to 0.65°N and about 400 km from land, as well as on Sao Vicente in the Cape Verde Islands about 1000 km of the West African coast.

In early 2008, air samples were also collected within West Africa, at various locations within Ghana, Ivory Coast, Sierra Leone and Gambia.

High West African PCB levels confirmed

The results were published by senior reporter Rosalinda Gioia from Lancaster University, UK, with collaborators from the Norwegian Institute for Air Research, NIVA Norwegian Institute for Water Research, the University of Oslo, USF College of Public Health, Florida, USA, and Euskal Herriko University, Bilbao, Spain.

The PCBs were extracted from the air samplers by established methods and analysed by GC/MS with electron ionisation, using deuterium-labelled PCBs as internal standards. Different sets of compounds, from tri- to heptachloro-PCBs were measured in selected ion monitoring mode.

The measurements agreed with those taken on the two previous cruises. The highest seaborne PCB levels, corresponding to 96-360 pg/m³, occurred between 14 and 7°N and coincided with winds blowing from the north, northeast and east. The lowest levels were found near the equator where the winds blew from the south, backing up the idea that the PCBs are land-based.

Typical PCB concentrations in urban parts of Europe are about 100 pg/m³, so these seaborne values are extraordinarily high, especially since they were taken 400 km from land.

The Cape Verde Island measurements were taken the same day as some of the sea measurements. They were in the range 6-99 pg/m³, lower than the measurements taken on ship, and the difference was attributed to the greater dispersion and dilution of PCBs as they travelled the extra 600 km to the Islands.

The land-based measurements in two of the four countries were also remarkably high. Total PCB levels in some regions of Gambia and Ivory Coast were each 300 pg/m³, whereas those in Sierra Leone were low at 12 pg/m³. The only country for which previously published data are available was Ghana and those levels agreed with the values measured here at 8.2-33 pg/m³.

West Africa - the dumping ground

So, the land and sea-based measurements, along with the direction of the prevailing winds, strongly suggest that the PCBs originate from land. But what are the principal sources?

One idea is that they originate from forest fires and biomass burning, which are prevalent across Africa, as confirmed by satellite imaging. However, modelling data could not account for the PCB levels. In addition, PAH levels measured on the ship and at Cape Verde were at their lowest when PCB levels were at their highest. PAHs are also produced by biomass combustion, so, clearly, there are key missing sources.

Gioia and the team pointed the finger at two principal sources. It is an unfortunate fact that Africa has become the illegal dumping ground for electronic waste. When computers and electronic devices have been stripped of their precious metals, the remaining cables, plastic and casings are often dumped or burnt. Burning releases airborne PCBs.

A second possibility is the dismantling of abandoned ships. In one bay in Mauritania, West Africa, an estimated 300 ships are littered around the harbour awaiting break up. PCBs were commonplace in ships in the 1960s-1980s, so are likely to be released once dismantling takes place.

The team declared that the exact sources of the PCBs should be identified, so that they can be disposed of safely. Their precise location and quantification will also enable them to be taken into account more accurately in global models of PCB distribution. Currently, African projections are well below the actual emissions, simply because the extent of PCB problem had not been recognised.

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.