General commission for terminology and neologisms4 describes bioaccumulation as a “process by which a pollutant present in a biotope penetrates or accumulates in some or all of a living organism and can become harmful; by extension, the result of this process.” In the strict sense of the word, bioaccumulation results from the gradual accumulation of a contaminant or toxic substance in an organism, from diverse sources, including the atmosphere, water and food, until an equilibrium is reached between accumulation and excretion of the substance5, with a concentration in the organism that is greater than that in the contamination sources. If this phenomenon is reproduced at each trophic level (with a cumulative increase in concentration of the substance as it moves up the food chain), the term used is bioamplification. The opposite process leads to dilution. Finally, if the living organism was exposed to higher environmental concentrations in the past than in the present, said past contamination may remain in some of its tissue (remanence), leading to an apparent imbalance with regard to the present lower concentrations of the contaminant in the environment. This phenomenon occurs when a substance fixes in the organism at a concentration that is lower than or equal to that of the original source, and stays there for a period whose length will depend on the speed at which the substance is excreted. Remanence can also be observed in abiotic environments (soils or sediments) when physicochemical processes cause a substance to be fixed in the environment long term. Observations and interpretations The presentations focused on observations carried out both in marine environments (Cardiff Bay, Sellafield, La Hague) and in terrestrial environments. In the case of the plant producing labelled molecules in Cardiff, a clear example of tritium bioconcentration was observed. The hypothesis concerning bioaccumulation/bioamplification applies if the tritium comes from tritiated organic molecules. The tritium content found as free tritium (HTO) and organically bound tritium (OBT) in marine fauna varies by factors between 1,000 and 10,000 with 4 Journal Officiel de la République française, Avis et Communications, 4 February 2010 respect to the concentrations found as HTO in the sea water For the Sellafield site (fuel reprocessing facility managed by BNGSL British Nuclear Group Sellafield Limited, which discharges tritiated water), the tritium content found as free tritium (HTO) or organically bound tritium (OBT) in marine fauna (fish, crustaceans and molluscs) varies by a factor of 10 with respect to the concentrations found as HTO in the sea water with 1 to 2 years hysteresis (time lag) between the maximum discharge values and the maximum tritium values in molluscs and flat fish. These observations were interpreted in different ways by various members of the working group. Some consider that the abnormally high concentrations measured in fish near Sellafield may result either from remanence in sediment labelling following previously large discharges or from the existence of tritiated organic molecules in the same water outflow. Others consider that this is a case of bioaccumulation which is related to the discharge of tritiated water. According to proponents of this view, the hypothesis of marine currents carrying tritiumlabelled organic molecules discharged by the Cardiff radiochemical plant is refuted by the fact that analysis carried out near the Wylfa nuclear power plant (NPP), on the west coast of the UK between Cardiff and Sellafield did not find any detectable presence of tritium in the marine fauna. Other members of the group felt they did not have enough information to form a view. For the La Hague site (fuel reprocessing facility run by AREVA NC, discharging tritiated water), the Institute for Radiological Protection and Nuclear Safety (IRSN) considers that the research into tritium in the environment around La Hague (joint IRSN-AREVA campaigns) do not show any tritium bioaccumulation / bioconcentration. It should be noted that values for tritium content found as HTO in the sea water around the Sellafield outflows in the Irish Sea and around the La Hague outflows in the Channel are substantially similar. The French Association for the control of radioactivity in the West (ACRO) reports that bioconcentration (by a factor between 2 and 7) was found in an older joint EDF-IRSN study (from the period 1981-1985) in a small number of available 5 IRSN, “Le tritium dans l’environnement”, Report DEI 200905
RkJQdWJsaXNoZXIy NjQ0NzU=