Trace metal speciation in the Yamaska and St. François Rivers (Quebec)

Abstract

Water and suspended sediment samples were collected at 12 stations on the Yamaska and St. François Rivers, located in southeastern Quebec, and were analyzed for the trace metals Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn. The suspended sediment samples were subjected to a sequential extraction procedure designed to partition the particulate trace metals into five fractions: (1) exchangeable; (2) bound to carbonates; (3) bound to Fe–Mn oxides; (4) bound to organic matter; and (5) residual.Although suspended sediment levels as well as total soluble and particulate trace metal concentrations were highly variable in time and space, speciation patterns for each metal proved reasonably constant. Very small proportions of all metals, except Cd and Mn, were found in the exchangeable fraction, whereas high levels of all metals were present in the residual fraction; Fe–Mn oxides and organic matter constituted important transport phases for most metals. Deviations from this general behaviour were occasioned by man-induced perturbations (e.g., inputs of municipal sewage or mine waste water). At stations influenced by such factors, total particulate metal concentrations increased and the relative contribution of the residual fraction decreased. The trace metal content of fraction 3 proved to be particularly sensitive to anthropogenic inputs; other phases acting as trace metal sinks included those liberated in fractions 1 (Cd, Cu, Ni, Zn), 2(Cu, Ni, Zn), and 4(Cu, Ni).