Copper and lead isotope records from an electroplating activity in sediments and biota from Sepetiba Bay (southeastern Brazil)

Alternatives to 137Cs for 210Pb dating validation in south America and in the Carribean region: Point and diffuse sources

As today the 137Cs fallout peak, in sediment cores, corresponds only to 25% of its initial concentration, alternatives to the use of 137Cs as a210Pb sediment dating validation tool are proposed. In highly industrialized bays, such as Guanabara Bay in the Rio de Janeiro metropolitan region, several chemical/compounds from the surrounding industry releases may be applied as validation tools. Chromium and copper profiles in a sediment core adequately fit the expected pattern due to the implementation of a chemical plant in 1958, reaching their maximum discharge in 1982 and subsequently decreasing due to the operation of a new wastewater treatment plant. A diffuse source such, as the PCB-based mixture Askarel, was also applied as an alternative validation tool, and the observed concentration profile reproduced the expected behavior, with increasing concentration after the Second World War and a decrease after the ban of this product in 1981. The observed Aroclor 1254 and 1260 mixture chlorination rates fit the most widely distributed PCB-based products in the country.

Zinc and copper isotope fractionation in metal leaching from hydrothermal ore deposits: Environmental implications for deep-sea mining

Deep-sea mining can remobilize large amounts of inert metals from hydrothermal seafloor massive sulfides (SMSs) into bioavailable toxic forms that are dissolved in the water column, potentially impacting marine ecosystems. It is thus critical to assess the impacts of deep-sea mining on the reactivities and behaviors of crucial elements (e.g., Zn and Cu) and their isotopes during mineral leaching processes. To this end, we conducted leaching experiments using different SMS mineral types (CuFe rich, Fe rich, and ZnFe rich) to assess metal releases and the isotope fractionations of Zn and Cu. Significant correlations were observed between Ni, Cu, Zn, Cd, and Pb concentrations in leachates and the SMSs, suggesting that metal leaching into seawater depended on individual SMS metal content. The Zn and Cu concentrations in leachates varied greatly by both SMS type and the leaching time. Zn concentrations from ZnFe rich SMSs exceeded the recommended effluent limits set by the IFC World Bank and the USEPA. SMS ore leachates exhibited Cu and Zn isotope ratios distinct from those of Indian Ocean deep seawater. The isotope fractionation magnitude (Δore-seawater) of Cu was more pronounced than that of Zn, likely due to the redox process involved in the leaching processes. In contrast, the Zn isotope signatures in leachates conserve those of minerals, although slight isotope fractionations occurred in solution following the adsorption and precipitation processes of Fe-oxyhydroxides. Our findings confirm that leveraging the chemical and isotope signatures of toxic metals offers a valuable approach for assessing the extent of metal contamination of leachates and mine tailings stemming from deep-sea mining operations, concerning their influence on the surrounding water columns.

Copper and zinc isotope systematics in different bivalve mollusk species from the French coastline: Implications for biomonitoring

Zinc (Zn) and copper (Cu) stable isotopic compositions have been analyzed in various species of bivalve mollusks worldwide, but no comprehensive systematic interspecies comparison exists. Thus, we assessed isotope differences between species harvested in emblematic French coastal ecosystems to unveil biologically driven Cu and Zn isotope fractionation patterns. Inter-species isotopic variability of Cu is larger than Zn, with organisms that regulate internal concentrations displaying preferential bioaccumulation of heavy isotopes. The degree of internal isotope fractionation decreases from mussels > clams > oysters, affecting Cu more than Zn. The less pronounced Zn inter-specie variability helps preserve source information more reliably. Spatial analysis of a single oyster species denotes thus an important isotope variability of environmental Zn sources, including natural, anthropogenic and dietary components. Overall, results highlight the importance of considering systematic offset in Cu and Zn isotope values when comparing data from different bivalve species.

The French Mussel Watch Program reveals the attenuation of coastal lead contamination over four decades

The mid-20th century industrial peak caused severe global lead (Pb) marine contamination. Although Europe initiated Pb emission reduction regulations in the 1980s, the short- and long-term impacts remain unclear. This study investigates the evolution of Pb contamination on the French coast through elemental and isotope analysis in oysters and mussels from the French "Mussel Watch" Program. Observations at 114 monitoring stations over four decades have shown decreasing Pb levels in these bivalve mollusks. In 1988, 95 % exceeded the background reference values; this level had dropped to 39 % by 2021. The Pb isotope ratios in bivalves from eight target sites revealed a reduction in bioaccumulated anthropogenic Pb, albeit without complete elimination. The long residence time of legacy Pb combined with inputs from diffuse urban sources likely explains the persistent presence of anthropogenic Pb on the French coast. This study endorses the importance of continuous biomonitoring to evaluate environmental regulations and policies.

Copper isotopes as a tool to trace contamination in mangroves from an urbanized watershed

This study investigates the chronology of copper (Cu) contamination and its stable isotopes within an emblematic Brazilian mangrove impacted by multiple urban and industrial Cu sources, deforestation, and eutrophication. In particular, it tests Cu isotopes as tracers of anthropogenic inputs into an anthropized watershed impacted by multiple sources. To do so, we used multi-isotopic approaches (δ65Cu, δ13C, and δ15N), elemental analyses (Al, Ca, Fe, P, Cu, C, and N), and selective and sequential extractions in a210Pb-dated sediment core. This geochemical "toolbox" allowed identifying two main stages of Cu evolution in the sediment core. In the first stage, before 1965, Cu isotope fingerprints responded to landscape changes, indicating a shift from marine to geogenic dominance due to the remobilization and erosion of terrestrial materials. In the second stage, after 1965, the sediment geochemical profile showed increased Cu total concentrations with a higher bioavailability (as reflected by sequential extraction data) accompanying changes in Cu isotope signatures towards anthropogenic values. The findings evidence that local industrial sources, possibly combined with diffuse urban sources, export Cu into downstream mangroves with a distinguishable isotope signature compared to natural values. This study demonstrates the applicability of Cu isotopes as new environmental forensic tools to trace anthropogenic sources in mangrove sediments. Incorporated into a robust geochemical toolbox that combines inorganic and organic proxies for sedimentary materials, this new tool provides a comprehensive understanding of Cu dynamics in mangrove ecosystems, shedding light on the historical and current sources of Cu.