CADMIUM AND LEAD CYCLING BETWEEN WATER, SEDIMENT, AND BIOTA IN AN ARTIFICIALLY CONTAMINATED MUD FLAT ON BORKUM (FRG)

Artificial contamination was accomplished by injecting Cd as a chloride and Pb as a nitrate into the caisson so as to maintain metal concentrations of 100 mu g/l in the inflowing water of each tidal cycle for 25 days. Most (85%) of the injected Cd remained in the soluble phase whereas most (90%) of the Pb was transferred to the particulate phase. Cyclic changes in particulate Cd and Pb concentrations occur and indicate that Cd is progressively taken by the SPM over each tidal cycle, but after an initial rapid uptake, particulate Pb concentrations remain relatively constant in the system. In the sediments, Cd concentrations decrease with depth but increase with time, and with the highest increases occurring in the surface sediment layers. Lead concentrations initially remain constant with depth, but eventually Pb becomes enriched in the top 3 cm of the sediments. Biota show an exponential increase in Cd and Pb during the experiment.