Accumulation of Cadmium and Polychlorinated Biphenyls by Mytilus edulis Transplanted from Pristine Water into Pollution Gradients

Abstract

Monitoring of bioavailable Cd and polychlorinated biphenyls (PCB) is technically feasible by transplanting mussels, Mytilus edulis, from a population with low contaminant levels into polluted waters elsewhere. This procedure improves resolution power between sites of investigation by minimizing population variance at the start of exposure experiments. In the current investigation, random samples (100 animals each) of similar-sized individuals (length class 4.0–5.0 cm) derived from a sublittoral Atlantic stock (western Ireland) were simultaneously exposed to selected locations in Dutch estuarine and marine waters. Although approximately equal yearly amounts of Cd (~50 t) reach the sea by way of the Scheldt and the Rhine–Meuse systems, accumulated Cd levels in M. edulis in the eastern part of the western Scheldt Estuary were clearly elevated after 60 d of exposure, whereas levels in mussels under Rhine–Meuse influence were not greatly enhanced. The literature suggests that this is partly due to different geochemical processes. Cadmium accumulation in M. edulis is a slow process in the field, and plateau levels are not reached after 60 d. Polychlorinated biphenyls probably reach plateau values within 2–3 mo. The data show clear bioavailable PCB gradients as a result of fluvial input into Dutch coastal waters both by the Scheldt and the Rhine–Meuse systems. Contrary to data for Cd, a conservative estuarine mixing behavior is suggested. Also unlike data for Cd, winter levels in M. edulis were higher by a factor of 2 as compared with summer values, both on the basis of ash-free dry weights and total lipids. Offshore PCB concentrations in transplanted mussels remained low but after 60 d were elevated above initial Atlantic levels.