Tracing multi-anthropogenic inputs in intertidal mudflat sediments using lead and zinc isotopes

Area of Science:

• Environmental Geochemistry
• Isotope Geochemistry
• Estuarine Science

Background:

• Intertidal mudflats serve as crucial archives for historical contamination in tropical estuaries.
• Isotopic approaches for tracing pollution in these environments are significantly underexplored.
• The Santos-Cubatão Estuarine System is a highly industrialized coastal region in Latin America.

Purpose of the Study:

• To reconstruct the contamination history of the Santos-Cubatão Estuarine System using lead (Pb) and zinc (Zn) isotopes.
• To integrate new isotopic data with existing elemental concentration data from a sediment core.
• To assess the effectiveness of isotopic tracers in identifying shifting pollution sources.

Main Methods:

• Analysis of Pb isotopic ratios (²⁰⁸Pb/²⁰⁶Pb, ²⁰⁶Pb/²⁰⁷Pb) and Zn isotopic compositions (δ⁶⁶Zn) in sediment cores.
• Integration of new isotopic data with previously published Pb and Zn concentration data.
• Comparison of isotopic signatures to differentiate between geogenic and anthropogenic Pb sources and track changes in Zn contamination.

Main Results:

• Pb isotopes distinguished pre-industrial geogenic signatures from later radiogenic Pb inputs linked to steel plant emissions.
• Zn isotopes revealed shifts in contamination sources, with heavier values indicating industrial processes and lighter values reflecting urban effluents post-1980s.
• Isotopic data identified early anthropogenic contamination signals missed by elemental concentration analysis.

Conclusions:

• Pb and Zn isotopes are sensitive tracers for reconstructing pollution histories in estuarine mudflats.
• Isotopic geochemistry offers a more refined understanding of contamination sources and their temporal variations compared to concentration data alone.
• This study highlights the utility of isotope geochemistry for legacy pollution assessments in global estuarine systems.