Stable isotope-based tracing of lead (Pb) pollution in aquatic environments: Source apportionment and implications

Aquatic system contamination with lead (Pb) is an increasing environmental problem due to its persistence, bioaccumulation, and toxic effects on aquatic organisms and humans. This review examines the sources, impacts, and tracing methods of Pb contamination in aquatic ecosystems, with a focus on stable isotopes as a tool for identifying Pb sources. Pb originates from both natural processes, such as geological weathering and atmospheric deposition, as well as human activities like industrial discharges, mining, vehicle emissions, and agricultural runoff. Phosphate-based fertilizers, which are often overlooked, significantly contribute to Pb pollution by causing its accumulation in soils and water bodies through surface runoff and irrigation. Pb isotopic ratios, commonly using ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb, effectively distinguish between ore deposits and environmental Pb sources. Techniques such as Multi-Collector Inductively Coupled Plasma Mass Spectrometry and Thermal Ionization Mass Spectrometry provide precise isotopic measurements, enabling accurate source identification. However, factors such as isotopic fractionation, complex source apportionment, analytical limitations, temporal changes, and spatial differences can affect accuracy. Case studies from China's Baiyin mining district, Italy's Sarno River, and France's Orne River highlight the success of Pb stable isotope analysis in differentiating pollutant sources from various human activities. Conversely, Ethiopian water bodies emphasize the urgent need for Pb isotope analysis to guide pollution control efforts. This review advocates for integrating stable isotope analysis into environmental monitoring and policy development as a key step in reducing Pb pollution in aquatic environments.