Neutron activation study of elementary composition (Ag, As, Au, Ba, Br, Ce, Co, Cr, Cs, Fe, K, La, Na, Rb, Sb, Sc, Se, Sm, Sr, Th, U and Zn) was performed on edible sea urchins (Paracentrotus lividus Lamarck) from marine creek area polluted by city sewages from Marseille (France) after a purifying plant was brought into operation. Concentration levels were higher in soft organic parts (alimentary canals and gonads) for all the elements except for Sr which showed a strong affinity for calcareous parts (tests, spines and masticating apparatus). Certain elements present in the soft organic parts are rarely found in the hard parts. More than half the elements studied show higher concentrations in Marseille samples than in the referential region of Port-Cros National Park (France). That must be due to sewage rejection for a large number of them. This hypothesis is confirmed with regard to elements the values of which decrease significantly with the distance from the sewage emission point, e.g. Cr, Fe and Zn, and a little less for Ag, Ba, Ce, Rb, Sb, Sc, Se, Sm and Th. These results raise a question: has that artificial change on the elementary composition any toxicological effects on the urchin populations? This question is discussed.
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