Zinc source differentiation in hydrothermal vent mollusks: Insight from Zn isotope ratios

Organotropism of metals and ZnCu isotope ratios in hydrothermal vent mussels (Bathymodiolus) and sea snails (Ifremeria and Alviniconcha): Implications for bioaccumulation mechanisms

This study investigated metal organotropism and ZnCu isotopic compositions in hydrothermal vent mussels (Bathymodiolus sp.) and sea snails (Ifremeria sp. and Alviniconcha sp.). In mussels, bioaccumulation of Al, V, Cr, Mn, Fe, Co, Ni and Zn occurred mainly in the byssus and digestive gland, whereas Cu, As, Ag, Cd, and Pb were found in the gills, suggesting that bioaccumulation of these metals occurs via the respiratory system. In sea snails, the digestive glands tended to have higher metal concentrations than other organs. Zn showed higher intratissue isotope variability than Cu. For Cu isotopes, the digestive glands of vent mollusks had the highest δ65Cu values. However, while Zn concentrations were consistently elevated in the digestive glands, δ66Zn values did not exhibit a corresponding trend. In vent mussels, during sequenced transport or metal partitioning processes after accumulation via the gills and digestive glands, Zn and Cu concentrations decreased with isotopic fractionation, indicating that lighter isotopes are preferentially used. Both sea snail species differed from mussels in that they preferentially accumulated lighter Zn isotopes in the digestive glands with higher Zn content. The metal and isotopic signatures accumulated in the internal organs of hydrothermal vent mollusks suggest species-dependent dietary strategies and mechanisms of uptake, accumulation, and detoxification. Our findings related to the organotropism of Zn and Cu isotopes offer new insights into the bioavailability and bioaccumulation processes of hydrothermal vent mollusks.

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.

Zinc isotopic signature in tropical soils: A review

The micronutrient cycling in tropical latitudes is an issue of great concern because tropical soils are not only suffering micronutrient deficiency, but also influencing the global cycling of trace metals. With the development of stable isotope techniques, Zn isotopic composition (δ⁶⁶Zn) has been an powerful tool to interpret the Zn behaviour, signature, and cycling in soils. This review compiles δ⁶⁶Zn ratios of ten types of soils from both tropical and non-tropical latitudes, to (i) discuss the Zn isotopic signature in tropical soils and at the interfaces of soil-plant-river-ocean, (ii) disclose the Zn mass balance in tropical latitudes, and (iii) provide an implication for the eco-environmental effects of Zn cycling in tropical latitudes. Zinc isotopic signature is constrained by soil constituents. Our review summarized that the precipitation of secondary Fe oxides and organic complexation in the aqueous phases are likely to result in the preferential preservation of light Zn isotopes in tropical soils. The extreme weathering and material leaching of tropical soils can remove large amounts of Zn and thus result in Zn deficiency in tropical latitudes and pose risks to plant growth. The removed Zn is likely to influence the instantaneous riverine δ⁶⁶Zn heavier than that of the crustal average. However, the modern oceanic δ⁶⁶Zn will ultimately approach those of the parent materials by mass balance, at large geological timescales. Future direction should be concerned with the isotopic studies on Zn speciation in tropical soils and the association of isotopic ratios with the flux of Zn to quantitatively estimate of the Zn mass balance in tropical regions. The prospect of this review is to help solve the issue of plant micronutrition, as well as riverine and marine bio-availablity.

Copper isotope composition of hemocyanin

BACKGROUND

Copper is a metal that plays a central role in biology, for example, as co-factor in various redox enzymes. Its stable isotopic composition is being used as tracer of its transport in living organisms and as a biomarker for diseases affecting its homeostasis. While the application of copper stable isotopes to biological studies is a growing field, there are presently no biological standards that are systematically analyzed in the different laboratories, as it is the case for geological samples (e.g., by using widely available basalt samples). It is therefore paramount for the community to establish such standard. Copper also binds oxygen in the respiratory protein, hemocyanin, in the hemolymph of mollusks and arthropods and is thus critical to respiration for these species.

METHODS

Here, the Cu isotope composition of hemocyanin of different modern species of mollusks and arthropods (Megathura crenulate Keyhole limpet, Limulus polyphemus Horseshoe crab and Concholepas concholepas Chilean abalone), as well as theoretical constraints on the origin of these isotopic fractionations through ab initio calculations are reported.

RESULTS

The isotopic fractionation factors for Cu(I) and Cu(II), both in hemocyanin and in seawater, predict an enrichment in the lighter isotope of Cu in the hemocyanin by over 1 permil compared to seawater. The hemocyanin of Chilean abalone and Horseshoe crab have Cu isotope compositions (δ65Cu = +0.63 ± 0.04‰ and +0.61 ± 0.04‰, respectively, with δ65Cu the permil deviation of the 65Cu/63Cu ratio from the NIST SRM 976 standard), similar to that of the octopus reported in literature (+0.62‰), that are undistinguishable from seawater, suggesting quantitative Cu absorption for these organisms. Conversely, the Keyhole limpet is enriched in the lighter isotope of Cu, which is in line with the ab initio calculation and therefore Cu isotopic fractionation during incorporation of Cu into the hemocyanin.

CONCLUSIONS

Because these hemocyanin standard samples are widely available, they could serve in the future as inter-laboratory standards to verify the accuracy of the Cu isotopic measurements on biological matrices.

A nationwide survey of trace metals and Zn isotopic signatures in mussels (Mytilus edulis) and oysters (Crassostrea gigas) from the coast of South Korea

Thirteen trace metals and Zn isotopic signatures were investigated in mussels and oysters collected from the coast of South Korea to evaluate their bioavailability in bivalve mollusks. The average Cu, Zn, and Cd concentrations were 2.6-17.7 times higher in oysters than mussels, and high biota sediment accumulation factors (>30) were observed for these metals in oysters. Except for Pb in mussels, most metals had no correlation with total sediment concentrations. In oysters, Fe, V, Cu, Zn, Sn, and Pb concentrations were significantly correlated with sediments. The average values of δ⁶⁶Zn_IRMM3702 in mussels, oyster, and sediments were +0.09‰, +0.12‰, and -0.06‰, respectively. Soft tissues of mussels and oysters with high Zn concentrations tended to contain lighter Zn isotopes. The results indicate that oysters are a better biomonitoring organism for metal contamination than mussels and can be used in the monitoring and management of coastal environments and ecosystems.