THE DISTRIBUTION OF HEAVY-METALS AND POLYCYCLIC AROMATIC-HYDROCARBONS IN THE SEDIMENTS OF THE OYSTER GROUNDS (NORTH-SEA)

Concentration distributions of heavy metals and polycyclic aromatic hydrocarbons (PAHs) were determined in sediments taken in the Oyster Grounds. Average concentrations in fine fraction (<63 μm) of the sediments of Cd, Cu, Hg, Pb, and Zn were 0.14, 21.8, 0.23, 49.2, and 118 μg·g-1, respectively. Average ΣPAH concentration was 1.82 μg·g-1. Vertical gradients within the sediment cores varied for all compounds and did not exhibit any one particular trend, probably because of bioturbation and extensive fishery in this highly productive area. A highly significant north to south trend appeared for Cd: average values increased from 0.06 μg·g-1 in the northern part to 0.42 μg·g-1 in the southern. Most of the PAHs showed an opposite gradient: average ΣPAH values decreased from 2.53 μg·g-1 in the north to 1.24 μg·g-1 in the southern part of the Oyster Grounds. Heavy-metal levels in Oyster Ground sediments were 5 to 10 times lower than in other North Sea sedimentation areas (e.g. the Wadden Sea and the German Bight) and in the river Rhine. The yearly sediment deposition in the muddy part of the Oyster Grounds was used to calculate the yearly load of the various heavy metals and PAHs. It was estimated that less than 0.03 to 0.3% of the total heavy-metal input to the North Sea reaches the sediments of the Oyster Grounds. © 1990.