Historical atmospheric mercury emissions and depositions in North America compared to mercury accumulations in sedimentary records

Abstract

Gold and silver production in North America (included United States, Canada and Mexico) released a large amount of mercury to the atmosphere until well into this century when mercury (Hg) amalgamation was replaced by cyanide concentration. Since then, emissions from industries have been the dominant anthropogenic sources of atmospheric Hg in North America as a whole. Past Hg emissions from gold and silver extractions in North America during the 1800s do not show a clear evidence of atmospheric deposition occurred at the coring sites considered in this study. Estimated atmospheric emissions of Hg in North America peaked in 1879 (at about 1708 t yr-1) and 1920 (at about 940 t yr-1), primarily due to Hg emissions from gold and silver mining. After the Great Economic Depression (1929) Hg emissions peaked again in the 1947 (274 t yr-1), in 1970 (325 t yr-1) and in 1989 (330 t yr-1) as result of increased Hg emissions from industrial sources, though improvements in the emissions control technology in United States and Canada have been substantial. Estimates of total atmospheric deposition fluxes of Hg to water and terrestrial receptors were in the range of 14.3-19.8 μg m-2 yr-1 in North America as a whole, and averaged 135 μg m-2 yr-1 (global background + local emissions) in the Great Lakes. These values were in good agreement with recent estimates reported in literature. The comparison of atmospheric Hg deposition fluxes with Hg accumulation rates in sediment cores suggests that atmospheric deposition was the major source of Hg entering the lakes system at coring sites, however, important contributions to Lake Ontario sediment cores sites from 1940 to 1970 were likely originated from local point sources (i.e. direct discharges).