Polluted shells all over the world

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recyclinage
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Polluted shells all over the world




by recyclinage » 30/07/09, 15:43

Lack of reliability of tests or appearance of new pollution? The debate over the toxicity of oysters from the Arcachon basin, regularly prohibited for consumption, is raging for the fifth consecutive year. Distraught, oyster farmers are worried about their future.

The case of French seashells is far from isolated. Over the past twenty years, toxic algae blooms have been increasing on coasts around the world and have become a source of concern for public authorities. Because shellfish are consumed more and more: in fifty years, world production has multiplied by fifteen. Scientists are now worried about the growing importance of "emerging" risks, linked to the effects of global warming and interactions between toxins, which are still poorly understood.

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French production at the forefront of Europe

Breeding. World production of bivalve molluscs (oysters, mussels, etc.) rose from 1 million tonnes in 1950 to 15 million tonnes in 2007.

Europe. With around 200 tonnes, two thirds of which are oysters, French production ranks first in Europe.

Consumption. The French are the first consumers in the world of fresh oysters, with 2 kg per year and per capita.

Employment. The 3 French companies in the shellfish sector employ 700 people and have a turnover of 20 million euros.

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To the misfortune of producers and lovers of mussels, clams and other oysters, the shellfish, by filtering the sea water, concentrate the pollutants.

Three types of contaminants accumulate there: chemical residues, microbiological pollution (linked to dysfunctions of treatment plants and agricultural activities) and, for the past twenty years, toxic substances produced by certain species of micro-algae . These can cause gastrointestinal or neurological disorders.

All regions of the world are affected by these blooms. "The United States and Canada are more concerned by paralyzing toxins and amnesia, which can produce serious poisoning. Fatal cases were recorded in Canada in the 1980s, observes Catherine Belin, director of the phytoplankton monitoring network and phycotoxins (REPHY) created by the French Research Institute for the Exploitation of the Sea (Ifremer) in 1984. Diarrheal toxins dominate in Europe. " This is the case in France, where the entire coastline is affected. Paralyzing or amnesic toxins are also spotted more occasionally. But no fatal intoxication has been identified in France.

The phenomenon was clearly characterized for the first time in the 1970s. Pollution then increased significantly in the 1990s, before stabilizing in the 2000s. In question: the ballast water from ships, which propagated toxic algae all over the globe. Local pollution is an aggravating factor: the influx of nitrogen and phosphorus from cities and farms promotes algal blooms.

Scientists are concerned today about the impact of global warming. Thus Ostreopsis, used to tropical waters, is proliferating more and more in the Mediterranean. This alga produces a toxic substance which disperses in the air, causing respiratory problems. Preventive beach closings have already taken place in France, Spain and Italy.

In the face of risks, a rigorous control system for the quality of water and shellfish has been put in place in France, the leading European shellfish country ahead of Spain and the world's leading consumer of oysters. Each year, sales bans are pronounced the equivalent of one month per year. It is this test system that is currently at the heart of the controversy surrounding Arcachon oysters.

Scientists speak of "atypical" cases. The biological tests, which consist in injecting extracts from the digestive glands of shellfish into mice, lead to the death of the animals within XNUMX hours, but are not confirmed by the usual additional tests. "We are in the presence of a toxicity that we do not understand, explains Sophie Krys, head of the toxin characterization unit at the French Food Safety Agency (Afssa). Something acts on the animal, but toxic phytoplankton are not found in the environment, nor toxins known during chemical investigation tests. "

The oyster farmers, heavily penalized economically, question the method. "We can no longer rely on the biological test alone, says Goulven Brest, president of the National Shellfish Committee. The results of chemical tests and observations in the natural environment must be taken into account."

Afssa points out, however, that the test on mice "remains the reference method at European level". It has the advantage of reacting to the presence of known or unknown toxins - including in terms of effects on human health - while chemical tests only target known molecules.

For oyster farmers, the reaction of mice is not necessarily synonymous with toxicity for humans. But scientists recommend the application of the precautionary principle. "There is damage to the animal, therefore potentially a risk for the consumer. The substances in question must be identified," continues Ms. Krys. A research program piloted by Afssa was launched at the end of 2007 in order to elucidate these cases. Several avenues are explored, including the synergies of action between toxins, still poorly understood, and the appearance of new phytoplankton.

The government, for its part, is playing it safe. The Minister of Food and Agriculture Bruno Le Maire, while saying he is "determined to set up an alternative test, capable of providing more details", refers to the European level. "The European Union aims to move towards more precise tests on the causes of toxicity. The European Health Safety Authority (EFSA) is working on the subject, one explains to the ministry. For the moment, the tests validated chemicals are not sufficient to achieve a level of safety equivalent to biological tests. "
Gaelle Dupont








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