The distribution and partition of zinc, copper, and lead in the sediments of the Saguenay fjord

Abstract

Zinc (Zn) concentrations vary between 43 and 145 ppm, copper (Cu) concentrations between 6 and 33 ppm, and lead (Pb) concentrations between 14 and 66 ppm in relation to sediment texture and location in the Saguenay fjord. The concentrations of the elements increase with decreasing grain size; the highest concentrations occur in the fine grained sediments (muds) in the upper part of the fjord and they decrease downstream. On the average, the fjord muds are enriched in Zn and Pb when compared to sediments from the St. Lawrence estuary and the open Gulf of St. Lawrence.Acetic acid extractions of the sediments indicate that 14 to 29% of the total Zn, 14 to 21% of the total Cu, and 12 to 25% of the total Pb is contributed by the non-detrital (acid soluble) fraction, and the remainder (70–88%) is contributed by the detrital (acid insoluble) fraction. Most of the Zn, Cu, and Pb in the detrital fraction is held in discrete sulphide minerals. These minerals accumulate at the same rate as other detrital sedimentary material in response to the present depositional conditions. Non-detrital Zn, Cu, and Pb contributions represent the portion of the total element content adsorbed by fine grained inorganic and organic material during transport and deposition. The distributions of non-detrital Pb and to a lesser extent of Zn and Cu in the fjord are apparently controlled by the downstream dispersal from local industrial sources of mercury (Hg)-rich terrestrial organic matter.