Studies on the pathways and effects of cadmium in controlled ecosystem encolosures

Two experiments were performed during 1975 and 1976, in which cadmium was added to seawater and its plankton enclosed in plastic containers moored in Saanich Inlet (Vancouver Island, Canada), as part of the CEPEX project. In both experiments, two enclosures (ca. 68 m³ each) were used; one was spiked with about 1.3 g l^-1 cadmium, while the other served as a control, to assess the fate of the added metal and its effect on marine phytoplankton. In both experiments, the pattern of biological events was found to be very similar for the cadmium-treated bag and for the control. Furthermore, there were no marked differences in the phytoplankton species composition, thus indicating that at this concentration level cadmium did not affect the ecosystem. The rate of removal of cadmium by biological processes was relatively slow. The fraction of metal accumulated (for 2 and 4 weeks, respectively) in the settling material was less than 1% for the cadmium-treated bags. Experiments on the mechanism of cadmium binding indicated that the major part of the particulate metla is loosely bound to the outer cell membranes.