Assessment of Zn pollution sources and apportionment in agricultural soils impacted by a Zn smelter in South Korea

•Zn levels and Pb isotopes indicated soil contamination of smelter origin.•Zn was spatially distributed along prevailing wind currents and river valley.•Zn also vertically moved to a maximum depth of 60 cm.•Pb isotopes of smelter origin and geologic origin were distinct.•Pb isotopes were successfully applied to source identification and apportionment. This study was conducted to assess the anthropogenic impact on the metal concentration in agricultural soils in the vicinity of a Zn smelter. We determined Pb isotope ratios to trace source of metals and calculate source apportionment. 19.7% of the agricultural soil samples had Zn concentrations exceeding the Korean worrisome level (WL). The isotopic variation in the contaminated agricultural soils reflected the input of contaminants derived from the Zn smelter. The spatial distribution of Zn concentrations and Pb isotopes suggested that the Zn smelter dust fallout was the major source of heavy metal pollution in the agricultural soils. Lead isotope compositions of soil horizon I was comparable to those of soil horizon II, indicating that smelter-origin Zn had migrated vertically. Binary mixing between Zn concentrates and background soils could explain the variations in Pb isotope ratios in the contaminated agricultural soils. Source apportionment calculations showed that for agricultural soils that were found to exceed the Korean countermeasure standard (CS), the average proportion of smelter-origin Zn was 45.8%–83.3% while for agricultural soils that exceeded the WL but were below the CS, the average proportion of smelter-origin Zn was 36.3%–68.1%. The remainder was derived from a geogenic source.