Problematic and methodological approach of the study of the bioaccumulation of trace elements in Delphinids

Because of their position at the end of the trophic network, their long life span, and their specificity of mammals adapted to marine life, Delphinids are considered as a particularly interesting biological material for ecotoxicological studies. However, confronted with many restrictions basically associated with sampling difficulties due to economic, technical and legal reasons, many authors have only published occasional studies on dolphin's contamination by trace elements. Thus, amongst the previous works published in this field, only a few of them had enough samples and biological and ecological information at their disposal, to enable them to conduct a thorough study supported by a statistical approach. Nevertheless, the collection of a "suitable" sample is far from being the only difficulty met in this field of research. As with many ecotoxicological approaches "in situ" the study of the bioaccumulation of trace elements is confronted with the following problems 1. the number and complexity of the influence of environmental factors, 2. the lack of knowledge concerning the biology and physiology of the studied organisms, 3. the uncertainty surrounding the physico-chemical behaviour of the elements analyzed. Despite a strong scientific interest, the weakness of the methodological approach of many works in this field currently affects their credibility. The continuation or even the development of this type of research depends on our capacity to define coherent objectives which will open the door for a solid scientific prospective making necessary the establishment of a common method of approach. We propose some points of reflection on this topic. Faced with this problematic and being based on a particularly large sample of specimens, an example of a method of approach and procedure of data analysis is proposed. This allows us to go beyond the simple establishment of the contamination levels to reveal and quantify the actions of the different factors taken into account. As an example, the results concerning the influence of the geographical localization on the determinism of the bioaccumulation of mercury will be developed