Metal stable isotopes in transplanted oysters as a new tool for monitoring anthropogenic metal bioaccumulation in marine environments: The case for copper

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.

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.

Human health risk attributed to consumption of seafood and recreation swimming in Negombo Lagoon, Sri Lanka: An assessment on lagoon water and inhabitant oysters (Crassostrea cucullata Born, 1778)

The Negombo Lagoon is a coastal lagoon influenced by local communities that introduce waste into its ecosystem. This study examined seven sewage entry points, out of which five sites were chosen for oyster sampling based on availability. Physicochemical and microbiological parameters of water (measured in triplicate at each site, n = 84) and oyster samples (total length, TL > 6 cm, n = 30) were assessed. Variation in regional coliform contamination was analyzed employing a one-way analysis of variance (ANOVA). Results indicated that the northern part of the lagoon exceeded recommended coliform thresholds for swimming (total coliform concentration (TCC) < 126 most probable number (MPN)) and seafood consumption (TCC < 100 MPN/g), indicating the presence of Escherichia coli. Water quality indices affirmed fecal pollution, except in the southern part of the lagoon. Furthermore, the study found high oyster consumption (76.7 %), elucidating that oysters from the northern part of Negombo Lagoon pose health risks.

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.

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.

Mercury Contamination as an Indicator of Fish Species' Trophic Position in the Middle Araguaia River, Brazil

This study evaluates the use of mercury (Hg) concentrations in fish muscle tissue to determine a species' trophic position (TP) in its environment. A campaign conducted in 2019 along 375 km in the middle Araguaia River basin, Brazil, resulted in 239 organisms from 20 species collected. The highest total mercury (THg) concentrations were found in Pellonacastelnaeana (6.93 µg·g-1, wet weight) and in Triportheus elongatus (3.18 µg·g-1, wet weight), whose TPs were different according to the FishBase database. However, they occupied the same trophic level in this study. The intra-specific comparison showed a difference in Hg concentrations between individuals captured in distinct sites. The study of the biota-sediment accumulation factor (BSAF) showed that spatiality interferes with a species' TP. Statistical analyses revealed that when we used a predicted species' TP based on each individual's size, it explained 72% of the variability in THg concentration across all fish species. Multiple regression analysis confirmed that standard length and FishBase values are positively associated with THg (R2 = 0.943). These results point to Hg as a viable indicator of a fish species' TP since it reflects regional, biological, and environmental factors, as demonstrated here for the middle Araguaia River.

Environmental assessment of oyster beds in the northern Arabian Gulf Coast of the United Arab Emirates

The United Arab of Emirates (UAE) hosts valuable coastal and marine biodiversity, and oysters are one of the habitants of its marine ecosystem. Oysters play an essential role in the nearshore coasts where they work as an active filter. They filter nutrients, phytoplankton, sediments, heavy metals, and toxins out of the water, which improves the water quality. This is the first study that characterizes oyster bed habitats in the UAE by analyzing water quality parameters, polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs)and heavy metals in water, sediments and oyster samples collected from five locations along the coasts of Sharjah, Ajman, and Umm al Quwain. Oyster bed areas supported a diverse assemblage of benthic life including oysters, scallops, pen shells, hard corals, and macroalgae. Mobile species in these habitats included groupers, emperors, snappers, sea snakes, among others. The phytoplankton assemblages were dominated by diatoms, dinoflagellates, and small cryptophytes. Harmful diatom Pseudonitzschia was found in all locations. No detectable concentrations of PAHs and OCPs were reported in this study, and water quality parameters were within the acceptable levels for the region. On the other hand, water quality index was reported marginal, mostly due to the presence of higher than acceptable concentrations of chromium and mercury in all sites studied. Bioconcentration factors concluded that oysters were able to bioconcentrate metals such as arsenic, cadmium, chromium, and zinc, when compared to water. No detectable concentrations of lead and mercury were reported in oysters, suggesting higher depuration rates for those metals.

Poly- and Perfluoroalkyl Substances (PFAS): Do They Matter to Aquatic Ecosystems?

Poly- and perfluoroalkyl substances (PFASs) are a group of anthropogenic chemicals with an aliphatic fluorinated carbon chain. Due to their durability, bioaccumulation potential, and negative impacts on living organisms, these compounds have drawn lots of attention across the world. The negative impacts of PFASs on aquatic ecosystems are becoming a major concern due to their widespread use in increasing concentrations and constant leakage into the aquatic environment. Furthermore, by acting as agonists or antagonists, PFASs may alter the bioaccumulation and toxicity of certain substances. In many species, particularly aquatic organisms, PFASs can stay in the body and induce a variety of negative consequences, such as reproductive toxicity, oxidative stress, metabolic disruption, immunological toxicity, developmental toxicity, cellular damage and necrosis. PFAS bioaccumulation plays a significant role and has an impact on the composition of the intestinal microbiota, which is influenced by the kind of diet and is directly related to the host's well-being. PFASs also act as endocrine disruptor chemicals (EDCs) which can change the endocrine system and result in dysbiosis of gut microbes and other health repercussions. In silico investigation and analysis also shows that PFASs are incorporated into the maturing oocytes during vitellogenesis and are bound to vitellogenin and other yolk proteins. The present review reveals that aquatic species, especially fishes, are negatively affected by exposure to emerging PFASs. Additionally, the effects of PFAS pollution on aquatic ecosystems were investigated by evaluating a number of characteristics, including extracellular polymeric substances (EPSs) and chlorophyll content as well as the diversity of the microorganisms in the biofilms. Therefore, this review will provide crucial information on the possible adverse effects of PFASs on fish growth, reproduction, gut microbial dysbiosis, and its potential endocrine disruption. This information aims to help the researchers and academicians work and come up with possible remedial measures to protect aquatic ecosystems as future works need to be focus on techno-economic assessment, life cycle assessment, and multi criteria decision analysis systems that screen PFAS-containing samples. New innovative methods requires further development to reach detection at the permissible regulatory limits.

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.

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.

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.

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

The advent of Multicollector ICP-MS inaugurated the analysis of new metal isotope systems, the so-called "non-traditional" isotopes. They are now available tools to study geochemical and ecotoxicological aspects of marine metal contamination and hence, to push the frontiers of our knowledge. However, such applications are still in their infancy, and an accessible state-of-the-art describing main applications, obstacles, gaps, and directions for further development was missing from the literature. This paper fills this gap and aims to encourage the marine scientific community to explore the contributions of this newly available information for the fields of chemical risk assessment, biomonitoring, and trophic transfer of metal contaminants. In the current "Anthropocene" epoch, metal contamination will continue to threaten marine aquatic ecosystems, and "non-traditional" isotopes can be a valuable tool to detect human-induced changes across time-space involving metal contaminants, and their interaction with marine biota.

Oyster arsenic, cadmium, copper, mercury, lead and zinc levels in the northern South China Sea: long-term spatiotemporal distributions, combined effects, and risk assessment to human health

Estuarine and coastal ecosystems are often considered vulnerable due to the complex biogeochemical processes and the human disturbances through a variety of pollution. Among environmental contaminants, heavy metals in estuarine and coastal ecosystems have been of increasing concern in environmental conservation. Long-term exposure to heavy metal contamination, mainly through food and water, could be harmful to human health. It is therefore critical to understand the quantitative comparisons and combined effects of different heavy metals in common seafood species, such as oysters. This work studied the long-term spatiotemporal trends and health risk assessment of oyster arsenic (As), cadmium (Cd), copper (Cu), mercury (Hg), lead (Pb), and zinc (Zn) levels in the coastal waters of northern South China Sea. Cultured oysters (Crassostrea rivularis) from 23 estuaries and harbors in the coastal areas of northern South China Sea in 1989-2015 were analyzed for the spatiotemporal trends of the six heavy metal levels. Metal pollution index (MPI), target hazard quotient (THQ), and hazard index (HI) were used for quantifying the exposure of the six heavy metals to human health through oyster consumption. Principal component analysis (PCA) was used for assessing the relative importance of the six metals in oyster heavy metal distribution patterns in the northern South China Sea. Overall, the As, Cd, Cu, Hg, Pb, and Zn levels in oysters from the northern South China Sea generally declined from 1989 to 2015, stayed relatively high (MPI = 2.42-3.68) during 1989-2000, gradually decreased since 2000, and slightly increased after 2010. Oyster heavy metal levels were highest in the Pearl River Estuary (MPI = 1.20-5.52), followed by west Guangdong and east Guangdong, Guangxi, and Hainan coastal waters. This pattern is probably because economics and industry around the Pearl River Estuary have been growing faster than the other areas of this work in the recent two decades, and it should be taken as a hotspot for the monitoring of seafood safety in southern China. Principal component analysis indicated that Cu, Zn, and Cd were the most important metals in the long-term distributions of oyster heavy metal levels in the northern South China Sea. Health risk assessment suggested that the risk of the six heavy metals exposure through oyster consumption were relatively high during 1989-2005 (THQ = 1.01-5.82), significantly decreased since 2005 (THQ < 1), and slightly increased after 2010.