Heavy metals (Cu, Zn, Pb, Cd) in sediment, zooplankton and epibenthic invertebrates from the area of the continental slope of the Banc d'Arguin (Mauritania)

The concentrations of copper, zinc, lead and cadmium in the surface sediment (upper 5 mm) were generally higher in the silt fraction than in the bulk sediment. No significant geographical trend in the metal concentrations of the surface sediments was found, nor a correlation between concentrations in bulk sediment as well as in the silt fraction and the \% silt could be established. In general, the metal concentrations in both bulk sediment and silt are lower, when compared to marine environments in other climatological regions. In zooplankton, the metal concentrations were relatively high: expressed in µg g–1 on a dry weight (D.W.) basis, they ranged from 15–90 for copper, 70–580 for zinc, 12–55 for lead and 4–10 for cadmium. In epibenthic invertebrate species, both in crustaceans and bivalve molluscs, the concentrations of copper, zinc, and lead were in the same order of magnitude as compared to corresponding species from other geographical latitudes. Cadmium concentrations were relatively low, ranging from 0.13–0.42 µg g–1 D.W. in the bivalve molluscs Pitaria tumens and from 0.04–0.27 µg g–1 D.W. in the shrimp Processa elegantula. Also in the crab species Ilia spinosa, Inachus sp. and Pagurus sp., the cadmium concentrations were low, varying between 0.1 and 0.2 µg g–1 D.W. No significant relation between the metal concentration in whole-body samples and sediment (either bulk or silt) was present. Also no gradient was apparent in concentrations in organisms sampled at different depths (5 to 200 m) along two off-shore transects perpendicular to the Banc d'Arguin. Data indicated lower metal concentration in epibenthic organisms from sampling stations along a northern transect (southwest of Cap Blanc) than in organisms from the southern transect, off Cap Timiris. Evidence was obtained for a considerable atmospheric input of heavy metals, in particular zinc and lead, in a certain area along the continental slope of the Banc d'Arguin