HEAVY-METALS (CU, ZN, PB, CD) IN SEDIMENT, ZOOPLANKTON AND EPIBENTHICINVERTEBRATES FROM THE AREA OF THE CONTINENTAL-SLOPE OF THE BANC-DARGUIN (MAURITANIA)

The concentrations of copper, zinc, lead and cadmium in the surface se diment (upper 5 mm) were generally higher in the silt fraction than in the bulk sediment. No significant geographical trend in the metal con centrations of the surface sediments was found, nor a correlation betw een concentrations in bulk sediment as well as in the silt fraction an d the % silt could be established. In general, the metal concentration s in both bulk sediment and silt are lower, when compared to marine en vironments in other climatological regions. In zooplankton, the metal concentrations were relatively high: expressed in mug g-1 on a dry wei ght (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 specie s, both in crustaceans and bivalve molluscs, the concentrations of cop per, zinc, and lead were in the same order of magnitude as compared to corresponding species from other geographical latitudes. Cadmium conc entrations were relatively low, ranging from 0. 13-0.42 mug g-1 D.W. i n the bivalve molluscs Pitaria tumens and from 0.04-0.27 mug g-1 D.W. in the shrimp Processa elegantula. Also in the crab species Ilia spino sa, Inachus sp. and Pagurus sp., the cadmium concentrations were low, varying between 0. 1 and 0.2 mug g-1 D.W. No significant relation betw een the metal concentration in whole-body samples and sediment (either bulk or silt) was present. Also no gradient was apparent in concentra tions 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 stati ons along a northern transect (southwest of Cap Blanc) than in organis ms from the southern transect, off Cap Timiris. Evidence was obtained for a considerable atmospheric input of heavy metals, in particular zi nc and lead, in a certain area along the continental slope of the Banc d'Arguin.