Lead isotopes combined with geochemical and mineralogical analyses for source identification of arsenic in agricultural soils surrounding a zinc smelter

摘要

As-contaminated soil samples were chosen to identify As sources near a Zn smelter where Zn contamination in soils was found to be of smelter origin. Based on the As concentrations and Pb isotopic compositions, high As levels in soils were originated from the geogenic source. There was no consistent trend in As concentrations with either depth or distance from the smelter, while the Pb isotopic compositions in soils varied regardless of As levels and were quite different from those of smelter origin. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) suggested that the high As concentrations were due to arsenopyrite and its alteration minerals, which were easily found but heterogeneously distributed within host rocks. A detailed investigation of As levels and Pb isotropic compositions along the predominant wind direction also supported that the As contamination was of geogenic origin unlike the Zn contamination. The atmospheric emissions from the smelter increased the Zn concentrations and decreased the Pb-206/Pb-207 ratios at surface layers, while the As concentrations occasionally exceeded the worrisome level at deep layers. According to the Pb isotropic compositions, about 21% of the As-contaminated soils were impacted by the smelter, in particular at the surface layer.