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Donax rugosus, a common bivalve mollusc in the coastal waters of Mauritania, has been studied for trace metal concentrations as a function of sampling site (from South of Mauritania to the North of this country) and of season (Sidoumou 1991; Sidoumou et al. 1992). In this paper, the uptake of cadmium was experimentally studied in the different organs of D. rugosus. Since metals such as cadmium, copper and mercury may alter calcium homeostasis (Allemand et al. 1989; Viarengo et al . 1988; Gnassia-Barelli et al. 1995), calcium uptakewas also studied in the animals treated with cadmium. Since calcium is taken up through specific channels, it appears that metals inhibit Ca uptake by interacting with these channels in the plasma membrane. Cadmium and calcium have very similar atomic radii (Jacobson and Turner 1980), thus cadmium may be taken up through the calcium channels, particularly through voltage-dependent channels (Hinkle et al. 1987) . The uptake of cadmium and calcium by D. rugosus was therefore also studied in the presence of the calcium channel blocker verapamil. MATERIALS AND METHODS D. rugosus was collected at depths between 0 and 2 m on theMauritania coast, 15 kms north of Nouakchott. Animals were transported to the laboratory and placed in plastic tanks filled with natural, aerated seawater (S = 36°/°°, T = 21°C ± l°C) under a light-dark regime (12 hr: 12 hr). After 3 days of acclimation, cadmium-uptake experiments w e re carried out at two cadmium concentrations (20 and 150 µg/L) . Clams were exposed for 48 and 85 hr. The uptake of cadmium was also studied on animals previously treated with verapamil (at 100 µM, treatment 1 hr before adding cadmium) , an organic inhibitor of calcium channels.During exposure, the bivalves were not fed, the seawater was renewed after 48 hr and the same treatment was Correspondence to: M. Roméo

--Ce travail a été réalisé dans le cadre d'un accord inter-universitaire :

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Lévrier Bay is located at the northern Atlantic Mauritanian coast, between 19 ° 20'N and 20 ° 40'N and between the coast and 17 ° 20W in the vicinity of Cap Blanc peninsula. This work aims at contributing to the assessment the impact of industrial development in the Lévrier Bay through the study of the toxicity and the spatio-temporal distribution of trace metals (Cd, Pb, Cu, Zn and Hg) in surface sediments, during the four hydrological seasons. The trace metal concentrations of the sediments are generally heterogeneous and vary according to the metal analyzed and the sampling site according to the order Zn> Cu>Pb> Cd>Hg. In fact, the present work shows higher average concentrations of metals studied in surface sediments than those found for the same metallic elements in previous recent studies at Lévrier Bay, which may be due to anthropogenic pressure in these areas. , especially since the different sites of the Bay are deprived of any sanitation system. In addition, the levels of these metals in the sediments of Lévrier Bay are below the international standards recommended for the toxicity assessment of sediments.