Metal contamination of natural surface soils from long-range atmospheric transport: Existing and missing knowledge

Abstract

This review focuses on the long-range atmospheric transport of metals to organic-rich surface soils (mostly 50–90% organic matter) in the temperate, coniferous, and boreal zones of North America and Europe. From various air-pollution related measurements (air, precipitation, moss, peat cores) Pb and Zn are known to be transported long distances in the air in large amounts. Arsenic, Cd, Hg, Sb, and Se are also typical representatives of long-range transported air masses, and there is evidence that Ag, Bi, In, Mo, Tl, and W belong to this group of elements. Through the use of “environmental archives” such as ice and peat cores it has become evident that long-range transport of pollutants and associated contamination of natural surfaces is not just a recent phenomenon. There is compelling evidence for widespread enrichment of surface soil horizons in Pb from long-range transport, and many studies support enrichment of Zn. Mercury is also generally elevated by anthropogenic emissions over natural levels in organic-rich surface soils, whereas results for Cd are less conclusive. There is evidence that As, Se, Ag, Mo, In, Sb, W, Tl, and Bi all are subject to some enrichment in organic-rich surface soils from long-range atmospheric transport, but studies are still few for most of these elements. With the exception of Pb, little is known about residence times of the elements in the organic-rich surface horizon, and more research is needed on this topic. Further studies are desirable on the temporal and spatial trends in supply of the above elements, which are poorly known in large parts of the northern temperate zone.Key words: natural soils, metals, long-range atmospheric transport, organic matter, lead, zinc, cadmium, mercury.