Uncovering the sources of soil lead in the Old Copper Basin (SW Poland): insights from Pb isotope geochemistry

Abstract

This study explores lead (Pb) isotopic signatures in soils in the Old Copper Basin in SW Poland, an area influenced by centuries of copper mining and smelting. Previous observations showed that Pb distribution in these soils differs from distributions of other metallurgical contaminants such as Cu or Ni, suggesting additional sources of Pb. To address this, we conducted isotopic analyses of topsoil and subsoil samples, including EDTA-extractable fractions, as well as representative rocks and slags. Isotopic ratios (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) were used to distinguish lithogenic, metallurgical, and atmospheric inputs. Subsoils displayed a wide isotopic range (²⁰⁶Pb/²⁰⁷Pb = 1.183–1.234), commonly increasing with depth and consistent with local rocks and ore sources. Topsoils showed more uniform and less radiogenic values (²⁰⁶Pb/²⁰⁷Pb = 1.172–1.193), forming a regionally consistent isotopic pattern that we define as the Lower Silesian Contemporary Pollution Signal (LSCPS). This signal is linked to long-range atmospheric deposition from industrial emissions. EDTA-leachable Pb in surface soils was isotopically less radiogenic than bulk ²⁰⁶Pb/²⁰⁷Pb and similar to LSCPS Pb, indicating mobility of this anthropogenic fraction. Some topsoil profiles outside direct mining areas showed elevated Pb with isotopic ratios not related to local ores or slags, pointing to external atmospheric sources. These results emphasize the complex origin of Pb contamination in post-industrial landscapes and demonstrate the value of Pb isotope geochemistry in tracing overlapping pollution signals.