Integrated geochemical speciation and isotopic fingerprinting of anthropogenic lead across agro-urban and industrial soil systems

Understanding the intricate geochemical behavior and isotopic signatures of lead (Pb) in agro-urban and industrial soils is essential for unraveling complex contamination pathways. This study aimed to examine the total concentration, geochemical speciation, and isotopic composition of Pb from agricultural (Agri), urban (Urb), and industrial (Ind) soil profiles of Islamabad, Pakistan. Inductively coupled plasma-mass spectrometry (ICP-MS), a modified eight-step sequential extraction procedure, and a multi-collector inductively coupled mass spectrometer (MC-ICP-MS) were used to measure the total concentration, geochemical classification, and isotopic composition of Pb, respectively. The highest concentration of Pb was found at Ind (105 ± 44.01 mg kg⁻¹) in surface soil samples followed by Agri (72 ± 42.3 mg kg⁻¹) and Urb (47 ± 28.6 mg kg⁻¹). Diversified contamination of Pb was found at both spatial and vertical soil profiles. The average ²⁰⁶Pb/²⁰⁷Pb isotopic ratios were 1.198 ± 0.010 at Agri, 1.189 ± 0.021 at Urb, and 1.178 ± 0.019 at Ind. The isotopic composition of ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb revealed anthropogenic inputs and geogenic sources responsible for Pb enrichment at the three soil profiles. The vehicular exhaust was reported to be the primary source of Pb at the Urb site i.e., 67 %. Whereas, industrial inputs and vehicular exhaust (48 %) were found responsible for Pb enrichment at the Ind site. The findings from this study provide a comprehensive geochemical and isotopic framework for tracing anthropogenic Pb sources, emphasizing the urgent need for implementing advanced remediation measures and regulatory policies to mitigate Pb contamination and protect ecosystem-human health.