The product transported by the Erika was a mixture of 10 % of light fluxing oil, 30 % of heavy fluxing oil and 60 % of products of vacuum distillation. Its density was very close to that of seawater. Transported heated, it had a high viscosity at ambient temperature (20,000 cSt at 10 °C). Therefore it was not chemically dispersible and, as a consequence, the response option consisting in spreading dispersant on the slicks either by planes or by ships was eliminated.
38 cSt (100°C)
On the day of the incident, Cedre received from the TotalFina refinery in Dunkirk 100 l of the fuel loaded on the Erika. Tests were immediately carried out in Cedre's test flume. It appeared that the product had no tendency to disperse naturally in water. It floated and hardly fragmented at all. Its viscosity increased within a day to 70,000 cSt while it formed an emulsion reaching 30 % water. The emulsion reached 50 % water (viscosity: 350,000 cSt) in two days and then stabilised. At sea, the fuel also formed an emulsion. However the water content remained around 30 %. Analysis carried out on samples collected on the shore showed water content nearing 50 %.
Emulsification increased the volume of pollutant drifting at sea and made it stickier. This allowed the French Navy to confirm that the heavy fuel spilled by the Erika would be difficult to recover and could be pumped only provided water was added to it.
A full analysis of the chemical composition of the product was subsequently carried out by the French Petroleum Institute (IFP) and other laboratories: the LASEM (French Navy Laboratory for Analysis Monitoring and Expertise), Cedre, the MNHN (National Museum of Natural History), IFREMER (French Institute for research and exploitation of the Sea) and the University of Bordeaux.
22 - 30 %
42 - 50 %
Resins and asphaltenes
21 - 36 %
The results of fragmentation depend on laboratory protocols. According to the nature and the polarity of the solvents used, the cuttings between the families can be noticeably different, which modifies their relative proportions. We can conclude that the fuel transported by the Erika contained about 25 % heavy products (resins and asphaltenes) and nearly 50 % aromatic hydrocarbons. Aromatic hydrocarbons included oil compounds with a toxic potential, either in the form of direct toxicity (intoxication), or by mutagenic or carcinogenic effect. The impact on the ecosystem depended on the conditions of exposure (solubility of the compounds, duration) or on the possibilities of transfer to the food chain.
Evolution of the product
Evaporation depends initially on the nature of the product spilled, but also on the prevailing conditions. It can be significant for some light crude oils (30 to 40 % for the pollution caused by the Amoco Cadiz). Heavy products like the Erika's are much less influenced by the evaporation process, which affects less than 10 % of their mass.
Heavy fuels are classed as insoluble in water. However, the heavy fuel of the Erika contained mono-aromatic (6.6%) and di-aromatic (5.9%) fractions that showed some solubility in water. Seawater contamination can also result from a fragmentation of the product due to wave action and water turbulence, causing the production of oil droplets and oil cakes of various sizes, able to drift according to movements in the water column. To support this assumption, it should be stressed that many small oil fragments were regularly found stranded on the beaches. The fact of dealing with an oil product characterised as insoluble does not exclude possible contamination of the water column.
The oil transported by the Erika was a heavy fuel used for industrial combustion (power plants, furnaces, cement factories...) and power supply to ships propelled by slow powerful diesel engines.