Resumen de Enhanced heavy metal concentrations in Mytilus edulis from the central North Sea

Thomas Borchardt, Siegfried Burchert, Ludwig Karbe, Rainer Zeitner

• The blue mussel Mytilus edulis was used for monitoring the heavy metal pollution of the southeastern North Sea. From 1983 to 1986 samples were collected from anchor chains of nautical buoys and from biological monitoring stations. Soft bodies were analysed for mercury, cadmium, copper, silver, zinc and lead by atomic absorption spectrophotometry. Mercury concentrations in mussels decreased from the inner German Bight towards the central North Sea, while cadmium and lead concentrations increased. Highest cadmium and lead levels were measured in the open sea. This is in contrast to the distribution of heavy metal concentrations in seawater. It is concluded that three mechanisms might be involved in this paradox: 1) due to changes in heavy metal speciation an increasing bioavailability counteracts sinking concentrations in the seawater on a transect from the coast to the open sea; 2) according to the pattern of residual currents a great part of the particle-bound pollutants brought into the sea at many dumping sites along the British coast settles and accumulates in the central North Sea; 3) at times oxygen deficiences in some parts of the North Sea lead to pronounced changes in redox conditions in sediments, thus allowing remobilisation.