A TENTATIVE MODEL OF CD UPTAKE IN POTAMOGETON-PECTINATUS IN RELATION TO SALINITY

The aim of this investigation was to study the influence of salinity on Cd uptake in submerged macrophytes using Potamogeton pectinatus as a model species and to examine the partitioning of Cd between sediment and water. Experiments were performed under controlled conditions where plants were grown either in Cd-contaminated sediment and water of different salinities, or in water with Cd and different salinities in the absence of sediment. Cadmium uptake in P. pectinatus from water decreased with increasing salinity, most likely due to Cd forming complexes with chloride and sulphate. In the presence of sediment, Cd uptake increased with increasing salinity, because Na+ and Mg2+ replaced Cd2+ in the colloids of the sediment, thereby increasing the Cd concentration of the water and subsequently uptake by plant shoots. Osmotic potential did not influence the release of Cd from the sediment or Cd uptake by the plant. Cadmium uptake by roots and the plant-available fraction of Cd in the sediment were not affected by salinity. Cadmium bound firmly to the sediment decreased with increased salinity. The results are summarized in a tentative model of Cd uptake in a submerged macrophyte species in relation to salinity. The importance of an increased release of heavy metals from polluted sediments in brackish coastal areas is discussed.