A major pollution incident is affecting the Atlantic coasts of France. In December 1999, the wreck off the coast of Finisterre of the Erika, an old oil tanker sailing under the Maltese flag and chartered to Total-Fina, caused the release of a considerable quantity of very dense hydrocarbon. The French Navy's efforts have been powerless to stop the progress of the oil slick which has become fragmented into numerous 'lenses'. The coastal islands, coves and beaches of southern Brittany, to the north of Charentes, have been polluted over more than 250 km, causing catastrophic mortalities, foremost amongst them the very numerous seabirds which overwinter in this sector.

The impact on the malacofauna is still difficult to estimate. Burrowing bivalves in bays covered by the pollutant, which have not been cleaned up immediately, are asphyxiated, leading to the complete eradication of populations of Cerastoderma, Venerupis, Spisula, Solen etc. as , also, of the meiobenthic fauna and the food chains involved in the economy of this shifting medium. The alteration of the substrate will impede or modify its recolonisation by larvae. In the oyster farms, the clogging of the sacks leads to the death of the oysters. Some oyster farms are completely destroyed, but the precautions taken by oyster farmers in erecting barrages have saved a part of the stocks and preserved healthy oysters for consumption.

The long term effects are difficult to foresee. Researches on bivalves have shown that the hydrocarbons affect the cells of the digestive gland and kidney and the haemocytes. The pollutants, transported by lipoproteins in the haemolymph, are absorbed by pinocytosis and become bound in the cell to a receptor complex associated with a thermal shock protein (HSP90). The dissociation of this complex produces a transcription factor which penetrates the nucleus and binds to specific regulatory sequences of DNA located upstream of the genes coding for cytochrome P 450 oxidative enzymes. The resulting build-up of monooxygenases allows the pollutants to be attacked by oxidation-reduction reactions and hydrolysis. The elimination of toxic free radicals (super-oxide anions, hydrogen peroxide) is accomplished by peroxisome enzymes (catalase, super-oxide dismutase). The second phase in the elimination of the pollutant is dependant on conjugation enzymes with endogenous ligands (glutathione, glucuronic acid) to produce soluble excretable molecules.

The activities involved in the elimination of the pollutant may provoke the destruction of the cells either through the accumulation of super-oxide anions or by altering the cells' specific functions - such as nutrition, excretion or defence. In heavily polluted harbour zones in Galicia, Spain, a decline in the index of quality of the mussel Mytilus galloprovincialis has been seen, together with an increase in the prevalence of parasites (Mytilicola intestinalis) associated with heavy mortalities.

Pierre E Lubet, Emeritus Professor,

University of Caen, France.

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