Distribution, transport, and sources of metals in marine sediments near a coastal lead smelter in northern New Brunswick

Abstract

Significant variations in metal concentrations occur in marine sediments collected from Chaleur Bay, an estuary located between northern New Brunswick and Quebec's Gaspésie. The bay receives metals from many sources including a lead smelter, a mercury-cell chlor-alkali plant, and numerous mined and unmined base-metal deposits. This study examines the dispersal patterns of metals released to the bay from natural and anthropogenic sources, and the processes that collect and redistribute these elements in the marine environment. Bottom sediments were collected from 124 sites in the bay, at distances up to 100 km away from the smelter. The ranges in metal and metalloid concentrations of 918 sediment subsamples are as follows, in mg/kg: As, 2.8 to 74; Cd, 0.02 to 69; Cu, 3.4 to 200; Hg, <0.01 to 2.4; Pb, 0.3 to 2000; and Zn, 22 to 3200. Dispersion of smelter effluents and atmospheric emissions by wind and/or nearshore currents has resulted in an area of elevated As, Cd, Cu, Hg, Pb, and Zn concentrations in surficial sediments within approximately 10 to 20 km of the smelter. The concentrations of most metals decrease sharply with increasing distance from the smelter; however, Pb concentrations exceed background levels in surface sediments throughout the bay. In sediments adjacent to the smelter, metal levels are highest at approximately 5 to 10 cmdepth and decrease toward the sediment surface, which may reflect the significant reduction in smelter emissions since the mid-1970s. Lead isotope ratios suggest that the surface enrichment of Pb throughout the bay is mainly derived from smelter emissions and historical leaded gasoline combustion.