Deposit and mobility of cadmium in a marsh-cove ecosystem and the relation to cadmium concentration in biota.

The study reported here presents the results of an investigation of a marsh-cove ecosystem heavily contaminated by cadmium. The most contaminated aquatic sediments were dredged in 1972-73, but the resuspension of the sediments and recycle of water from the dredge spoil resulted in reestablishment of a large contaminated sediment bed with concentrations very similar to those observed before dredging. The stability of the sediment concentrations and shallow depth of the cadmium in the sediments indicate that the deposit is relatively stable in agreement with the expectations based on the water chemistry of the system. Uptake does occur in both marsh and aquatic plants and all species of animals tested. Significantly elevated concentrations are observed compared to noncontaminated areas; however, edible portions of most fish do not appear to present a hazard. Crabs appear to present the most likely source of a hazard to humans. This potential hazard is still under investigation. The dredging removed about 5.5 MT of cadmium, about one-fourth of that originally estimated to be present, but twice that amount is found to be in the cove sediments 3 to 4 years after dredging. No appreciable improvement in the ecosystem has been made, and more careful consideration should be given to the need for decontamination and the method of removal of contaminated aquatic sediments in any future case.