Cadmium in seawater recorded by mussels: regional decline established

Abstract

The mussel Mytilus edulis is used as a quantitative indicator of dissolved cadmium in the water of the K~eler Forde in comparison with a reference site in the b e l e r Bucht (Western Baltic Sea). As recorded by the mussel, the baseline Cd concentration in the h e l e r Bucht declined from ca 65 ng I ' in 1980 to 35 ng I ' in 1984. Recalculations of literature data suggest that the 1975-1976 Keler Bucht level was ca 110 ng 1' The 'normal' distribution of dissolved Cd in the Kieler Forde was characterized by ca 140 % of the baseline in the harbour area, 85 % in the inner fjord, and 120 to 140% in the outer fjord. Other patterns indicated by the mussel are considered to reflect occasional coincidence of hydrographic stagnation and specific events (harbour dredging, sewage pollution, industrial discharges). After collapses of oxybiotic life the mussel indicated approximately half normal Cd levels, but there is doubt that 'mussel watch' records may be relied upon if the mussels had been affected by anoxic conditions. 'Mussel watch' estimates of chemical water quality documented a downward trend of dissolved Cd in the SW Kieler Bucht, which corresponds to the information available from analytical seawater chemistry. According to the regional hydrography, t h s is conceived to reflect a decline of dissolved Cd and possibly other metals on a broader geographical scale. Implications suggested relate to the following of natural fluxes in the management of chemically similar wastes.