Assessment of trace metal pollution in roof dusts and soils near a large Zn smelter.

The spatial extent of dust emissions from a Zn smelter was assessed based on metal concentrations in roof dust samples. In addition, the vertical mobility of metal loads in soils was assessed from metal concentrations and Pb isotopic compositions. Moreover, the source apportionment of metals in the roof dusts and soils was estimated using Pb isotopes. A total of 13 roof dust and 11 smelter dust samples were collected respectively from residential houses and smelter stacks. The vertical distribution in soils was assessed at 10 cm intervals in four sites along the predominant wind direction. High metal concentrations were found in the roof dusts, which were enriched in Zn, Pb, Cd, and Cu by a factor of 48-937, 13-169, 161-3400 and 10-135, respectively, compared to the regional background values of soils, depending on the distance from the smelter. Horizontal extents of the airborne metal transport were estimated to exceed the impact radius (<4 km) calculated by a numerical model. As for soils, the metal concentrations were high in the surface layer and decreased abruptly with depth. The vertical extent of the metal contamination was found up to 60 cm. Considering the operational period of the smelter, the Pb migration rate was 0.4-1.3 cm/year and the farmlands showed higher penetration rates than the other sites, probably due to agricultural practices. The Pb isotope compositions for the contaminated soils lay on a mixing line between the anthropogenic Pb of the smelter and the geogenic Pb of the background soils, which confirmed that the emission and deposition of the airborne particles produced by the smelter contributed to 49-83% of trace metals in the surface soils. Similarly, the Pb isotopic compositions of the roof dusts indicated that most of Pb was derived from the smelter, in particular, from the casting and leaching stacks.