Heavy metal concentrations in molluscs from the Senegal coast.

Bivalve molluscs from the Western coast of Senegal were sampled and measured for their cadmium, copper and zinc concentrations. This part of Africa has not been studied as regards heavy metal concentrations in the molluscs. The collected species are two small African bivalve molluscs, living in the sand: Cardita ajar and Dosinia isocardia; the African mussel Perna perna which is the only mussel of this genus in the Western coast of Africa and the oyster Crassostrea gasar, which lives in mangroves attached to the rhizophores, in the intertidal zone. C. gasar and C. ajar present higher cadmium concentrations, respectively 6.82+/-0.54 and 13.77+/-0.80 microg Cd/g (d.w.) than the two other species (D. isocardia: 3.88+/-0.31 microg/g and P. perna 2.37+/-0.22 microg/g. Copper and zinc concentrations are in the range of the published values for C. gasar and P. perna collected elsewhere in Africa. The results suggest that cadmium may be present in high concentrations in Senegalese waters where upwellings occur.

Heavy metal distribution in different fish species from the Mauritania coast.

Cadmium, copper, zinc and mercury concentrations were determined in pelagic and benthic fishes from the Mauritania coast. The pelagic fishes consisted of the round sardinella Sardinella aurita (Clupeidae), the chub mackerel Scomber japonicus (Scombridae) and the Atlantic horse mackerel Trachurus trachurus (Carangidae). Four benthic species were considered, three Serranidae: the painted comber Serranus scriba, the golden grouper Epinephelus costae, and the Niger hind Cephalopholis nigri and one Mullidae: the West African goatfish Pseudupeneus prayensis. Cadmium, copper, zinc and mercury concentrations are low in the edible muscles of the pelagic species. In the benthic fishes, metals could be determined also in the gills and liver. Cadmium and copper were present in relatively low levels in the muscle (< or = 0.06 microgram Cd g-1 dry wt., < or = 1.6 micrograms Cu g-1 dry wt.) and gills (< or = 0.23 microgram Cd g-1, < or = 3.1 micrograms Cu g-1) and higher levels are encountered in the livers (< or = 51 micrograms Cd g-1, < or = 49.1 micrograms Cu g-1). Zinc concentrations in the muscle are low (< or = 20 micrograms Zn g-1 dry wt.), the concentrations in the gills (< or = 120 micrograms Zn g-1) approach those of the livers for C. nigri and P. prayensis or are higher in the case of S. scriba and E. costae. Mercury concentrations in the gills and muscle of the pelagic species are very low, higher quantities are found in the livers of the benthic species. The metal concentrations in all the fishes analysed, which are restricted to approximately 40 specimens, are low except those found for cadmium in the livers of the benthic fishes.