"Non-traditional" stable isotopes applied to the study of trace metal contaminants in anthropized marine environments

Combined copper isotope and elemental signatures in bivalves and sediments from the Korean coast: Applicability for monitoring anthropogenic contamination

This study investigates the applicability of elemental and Cu isotope compositions in sediments and bivalves from the Korean coast to monitor anthropogenic Cu contamination. Sediments with high Cu (>64.4 mg/kg) and/or moderate enrichment levels (EFCu) exhibit homogenous δ65CuAE647 values (-0.12 to +0.16 ‰), suggesting similar anthropogenic Cu fingerprints along the Korean coast. Sediments with Cu concentrations near natural background levels (< 20.6 mg/kg) display large isotopic variability (Δ65Cumax-mim: ~0.8 ‰), encompassing those from sediments under anthropic influences. We hypothesize that Cu isotopic compositions of Korean geology are heterogeneous, therefore, natural end-members of source mixing models should be established locally at small scales. Cu concentrations in Oysters correlate with sediments, and their isotopic compositions are more suitable for monitoring Cu contamination, while mussel's regulatory mechanisms seem to affect source records. The current Cu isotope data will help to detect shifts attributable to anthropic contamination in future biomonitoring.

Seasonal and multi-decadal zinc isotope variations in blue mussels from two sites with contrasting zinc contamination levels

Zinc (Zn) isotope compositions in soft mussel tissues help identify internal biological processes and track coastal Zn sources in coastal environments, thus aiding in managing marine metal pollution. This study investigated the seasonal and multi-decadal Zn isotope compositions of blue mussels (genus Mytilus) from two French coastal sites with contrasting Zn environmental contamination. Concurrently, we characterized the isotope ratios of sediments and plankton samples at each site to understand the associations between organisms and abiotic compartments. Our primary objective was to determine whether these isotope compositions trace long-term anthropogenic emission patterns or if they reflect short-term biological processes. The multi-decadal isotope profiles of mussels in the Loire Estuary and Toulon Bay showed no isotope variations, implying the enduring stability of the relative contributions of natural and anthropogenic Zn sources over time. At seasonal scales, Zn isotope ratios were also constant; hence, isotope effects related to spawning and body growth were not discernible. The multi-compartmental analysis between the sites revealed that Toulon Bay exhibits a remarkably lower Zn isotope ratio across all studied matrices, suggesting the upward transfer of anthropogenic Zn in the food web. In contrast, the Zn isotope variability observed for sediments and organisms from the Loire Estuary fell within the natural baseline of this element. In both sites, adsorptive geogenic material carrying significant amounts of Zn masks the biological isotope signature of plankton, making it difficult to determine whether the Zn isotope ratio in mussels solely reflects the planktonic diet or if it is further modified by biological homeostasis. In summary, Zn isotope ratios in mussels offer promising avenues for delineating source-specific isotope signatures, contingent upon a comprehensive understanding of the isotope fractionation processes associated with the trophic transfer of this element through the plankton.

The use of copper as plant protection product contributes to environmental contamination and resulting impacts on terrestrial and aquatic biodiversity and ecosystem functions

Copper-based plant protection products (PPPs) are widely used in both conventional and organic farming, and to a lesser extent for non-agricultural maintenance of gardens, greenspaces, and infrastructures. The use of copper PPPs adds to environmental contamination by this trace element. This paper aims to review the contribution of these PPPs to the contamination of soils and waters by copper in the context of France (which can be extrapolated to most of the European countries), and the resulting impacts on terrestrial and aquatic biodiversity, as well as on ecosystem functions. It was produced in the framework of a collective scientific assessment on the impacts of PPPs on biodiversity and ecosystem services in France. Current science shows that copper, which persists in soils, can partially transfer to adjacent aquatic environments (surface water and sediment) and ultimately to the marine environment. This widespread contamination impacts biodiversity and ecosystem functions, chiefly through its effects on phototrophic and heterotrophic microbial communities, and terrestrial and aquatic invertebrates. Its effects on other biological groups and biotic interactions remain relatively under-documented.

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

An old electroplating plant in Sepetiba Bay discharged metal-enriched wastes into the surrounding mangroves for 30 years (from the 1960s to 1990s), resulting in a hotspot zone of legacy sediments highly concentrated in toxic trace metals. This study applies Cu and Pb isotope systems to investigate the contributions of past punctual sources relative to emerging modern diffuse sources. The electroplating activity imprinted particular isotopic signatures (average δ⁶⁵Cu_SRM-976: 0.4 ‰ and ²⁰⁶Pb/²⁰⁷Pb: 1.14) distinct from the natural baseline and urban fluvial sediments. The isotopic compositions of tidal flat sediments show intermediate isotope compositions reflecting the mixing of Cu and Pb from the hotspot zone and terrigenous materials carried by rivers. Oyster isotope fingerprints match legacy sediments, attesting that anthropogenic Cu and Pb are bioavailable to the biota. These findings confirm the interest in combining two or more metal isotope systems to discriminate between modern and past metal source emissions in coastal environments.

Isotopic (Cu, Zn, and Pb) and elemental fingerprints of antifouling paints and their potential use for environmental forensic investigations

Antifouling paints (APs) are one of the important sources of Cu and Zn contamination in coastal environments. This study applied for the first-time a multi-isotope (Cu, Zn, and Pb) and multi-elemental characterization of different AP brands to improve their tracking in marine environments. The Cu and Zn contents of APs were shown to be remarkably high ∼35% and ∼8%, respectively. The δ⁶⁵Cu_AE647, δ⁶⁶Zn_IRMM3702, and ²⁰⁶Pb/²⁰⁷Pb of the APs differed depending on the manufacturers and color (-0.16 to +0.36‰, -0.34 to +0.03‰, and 1.1158 to 1.2140, respectively). A PCA analysis indicates that APs, tires, and brake pads have also distinct elemental fingerprints. Combining isotopic and elemental ratios (e.g., Zn/Cu) allows to distinguish the environmental samples. Nevertheless, a first attempt to apply this approach in highly urbanized harbor areas demonstrates difficulties in source apportionments, because the sediment was chemically and isotopically homogeneous. The similarity of isotope ranges between the harbor and non-exhaust traffic emission sources suggests that most metals are highly affected by urban runoff, and that APs are not the main contributors of these metals. It is suspected that AP-borne contamination should be punctual rather than dispersed, because of APs low solubility properties. Nevertheless, this study shows that the common coastal anthropogenic sources display different elemental and isotopic fingerprints, hence the potential for isotope source tracking applications in marine environments. Further study cases, combined with laboratory experiments to investigate isotope fractionation during releasing the metal sources are necessary to improve non-traditional isotope applications in environmental forensics.

Characteristics of metal pollution and multi-isotopic signatures for C, Cu, Zn, and Pb in coastal sediments from special management areas in Korea

The concentrations and isotopic compositions of carbon (C), copper (Cu), zinc (Zn), and lead (Pb) in coastal sediments were analyzed to identify potential pollution sources. High concentrations of total organic carbon (TOC) and metals were found close to cities and industrial areas. The isotopic compositions of C, Cu, Zn, and Pb tended to decrease as their concentrations increased. Bi-plots between δ⁶⁵Cu and δ⁶⁶Zn showed that the isotopic compositions in most coastal sediments, except sediments around a smelter, were similar to the isotopic compositions of road dust in urban and industrial areas of Korea. Our results suggest that heavy metal pollution in coastal sediments is greatly influenced by the pollution source, such that most metals originate from traffic and industrial activities in the urban environment. This analysis of multiple isotopes provides insights concerning the transport mechanisms and clarifies potential sources of metal contamination in coastal environments.

Isotopic compositions of copper and zinc in plankton from the Mediterranean Sea (MERITE-HIPPOCAMPE campaign): Tracing trophic transfer and geogenic inputs

This study uses Cu and Zn isotopic compositions as proxies of sources and metal transfers in the planktonic food webs from the Mediterranean Sea. Plankton was collected in spring 2019 in the deep chlorophyll maximum (DCM) along a North-South transect including coastal and offshore zones (MERITE-HIPPOCAMPE campaign). δ⁶⁵Cu and δ⁶⁶Zn were determined on four planktonic size fractions from 60 to 2000 μm. Combined δ⁶⁵Cu and δ⁶⁶Zn with geochemical tracers (Ti, particulate organic phosphorus) showed that geogenic particles were ubiquitous with plankton assemblages. The δ¹⁵N ecological tracer showed that planktonic food web was enriched in heavy isotopes of Cu and Zn in the higher trophic levels. δ⁶⁵Cu were correlated with picoplankton in the offshore zone, and with zooplankton in the southern coastal zone. Firmicutes bacteria were found correlated with δ⁶⁶Zn in northern and southern coastal zones suggesting decomposition of particulate matter at the DCM. These findings suggest that biogeochemical process may impact Cu and Zn isotopy in the planktonic community.

Emerging applications of high-precision Cu isotopic analysis by MC-ICP-MS

As a component of many minerals and an essential trace element in most aerobic organisms, the transition metal element Cu is important for studying reduction-oxidation (redox) interactions and metal cycling in the total environment (lithosphere, atmosphere, biosphere, hydrosphere, and anthroposphere). The "fractionation" or relative partitioning of the naturally occurring "heavy" (⁶⁵Cu) and "light" (⁶³Cu) isotope between two coexisting phases in a system occurs according to bonding environment and/or as a result of a slight difference in the rate at which these isotopes take part in physical processes and chemical reactions (in absence of equilibrium). Due to this behaviour, Cu isotopic analysis can be used to study a range of geochemical and biological processes that cannot be elucidated with Cu concentrations alone. The shift between Cu⁺ and Cu²⁺ is accompanied by a large degree of Cu isotope fractionation, enabling the Cu isotope to be applied as a vector in mineral exploration, tracer of origin, transport, and fate of metal contaminants in the environment, biomonitor, and diagnostic/prognostic marker of disease, among other applications. In this contribution, we (1) discuss the analytical protocols that are currently available to perform Cu isotopic analysis, (2) provide a compilation of published δ⁶⁵Cu values for matrix reference materials, (3) review Cu isotope fractionation mechanisms, (4) highlight emerging applications of Cu isotopic analysis, and (5) discuss future research avenues.