Distribution of rare earth elements and assessment of anthropogenic gadolinium in estuarine habitats: The case of Loire and Seine estuaries in France.

Rare earth elements (REEs), attractive to society because of their applications in industry, agriculture and medicine, are increasingly released into the environment especially in industrialized estuaries. This study compared the REE distribution in the abiotic compartments: water (dissolved phase (<0.45 µm), suspended particulate matter (SPM)) and sediment of the Loire and Seine estuaries (France). A total of 8 and 6 sites were investigated in the Loire and Seine, respectively, as well as 5 additional offshore sites for the Loire. Total REE concentrations were higher in the Loire for the dissolved phase (93.5 ± 63.3 vs 87.7 ± 16.2 ng/L), SPM (173.9 ± 18.3 vs 114.0 ± 17.8 mg/kg dw) and sediments (198.2 ± 27.9 vs 73.2 ± 27.4 mg/kg dw), explained by higher geogenic inputs. Individual REE contributions along with normalization highlighted heavy REE enrichments and Gd positive anomalies in the dissolved phase of the two estuaries, whereas REE distributions in SPM and sediments followed the natural abundance of the REE classes. The calculated Gd anomalies in the dissolved phase were higher in the Seine (9.7 ± 3.4) than in the Loire (3.0 ± 0.8), corresponding to 88.3 ± 5.1 % and 64.4 ± 11.1 % of anthropogenic Gd. This demonstrates a higher contamination of the Seine estuary, certainly due to the difference in the number of inhabitants between both areas involving different amounts of Gd used in medicine. The offshore sites of Loire showed lower total REE concentrations (55.8 ± 5.8 ng/L, 26.7 ± 38.2 mg/kg dw and 100.1 ± 11.7 mg/kg dw for the dissolved phase, SPM and sediments, respectively) and lower Gd anomalies (1.2 ± 0.2) corresponding to only 13.3 ± 3.9 % of anthropogenic Gd, confirming a contamination from the watershed. This study comparing two major French estuaries provides new data on the REE distribution in natural aquatic systems.

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.

Ancestors' Gift: Parental Early Exposure to the Environmentally Realistic Pesticide Mixture Drives Offspring Phenotype in a Larger Extent Than Direct Exposure in the Pacific Oyster, Crassostrea gigas.

Marine organisms are threatened by the presence of pesticides in coastal waters. Among them, the Pacific oyster is one of the most studied invertebrates in marine ecotoxicology where numerous studies highlighted the multiscale impacts of pesticides. In the past few years, a growing body of literature has reported the epigenetic outcomes of xenobiotics. Because DNA methylation is an epigenetic mark implicated in organism development and is meiotically heritable, it raises the question of the multigenerational implications of xenobiotic-induced epigenetic alterations. Therefore, we performed a multigenerational exposure to an environmentally relevant mixture of 18 pesticides (nominal sum concentration: 2.85 µg·L-1) during embryo-larval stages (0-48 hpf) of a second generation (F1) for which parents where already exposed or not in F0. Gene expression, DNA methylation, and physiological end points were assessed throughout the life cycle of individuals. Overall, the multigenerational effect has a greater influence on the phenotype than the exposure itself. Thus, multigenerational phenotypic effects were observed: individuals descending from exposed parents exhibited lower epinephrine-induced metamorphosis and field survival rates. At the molecular level, RNA-seq and Methyl-seq data analyses performed in gastrula embryos and metamorphosis-competent pediveliger (MCP) larvae revealed a clear F0 treatment-dependent discrimination. Some genes implicated into shell secretion and immunity exhibited F1:F0 treatment interaction patterns (e.g., Calm and Myd88). Those results suggest that low chronic environmental pesticide contamination can alter organisms beyond the individual scale level and have long-term adaptive implications.

Molecular and phenotypic effects of early exposure to an environmentally relevant pesticide mixture in the Pacific oyster, Crassostrea gigas.

Early life stages are crucial for organism development, especially for those displaying external fertilization, whose gametes and early stages face environmental stressors such as xenobiotics. The pacific oyster, Crassostrea gigas, is considered a model species in ecotoxicology because of its ecological characteristics (benthic, sessile, filter feeding). So far studies have investigated the impact of xenobiotics at embryotoxic, genotoxic and physiological endpoints, sometimes at the multigenerational scale, highlighting the role of epigenetic mechanisms in transmitting alterations induced by exposure to single xenobiotics. However, to date, little is known about the impact of environmentally-mimicking contaminants cocktails. Thus, we examined the impact of an early exposure to environmentally relevant mixture on the Pacific oyster life history. We studied transcriptomic, epigenetic and physiological alterations induced in oysters exposed to 18 pesticides and metals at environmental concentration (nominal sum concentration: 2.85 µg.L-1, measured sum concentration: 3.74 ± 0.013 µg.L-1) during embryo-larval stage (0-48 h post fertilization, hpf). No significant differences in embryo-larval abnormalities at 24 hpf were observed during larval and spat rearing; the swimming behaviour of exposed individuals was disturbed, while they were longer and heavier at specific time points, and exhibited a lower epinephrine-induced metamorphosis rate as well as a higher survival rate in the field. In addition, RNA-seq analyses of gastrula embryos revealed the differential expression of development-related genes (e.g. Hox orthologues and cell cycle regulators) between control and exposed oysters. Whole-genome DNA methylation analyses demonstrated a significant modification of DNA methylation in exposed larvae marked by a demethylation trend. Those findings suggest that early exposure to an environmentally relevant pesticide mixture induces multi-scale latent effects possibly affecting life history traits in the Pacific oyster.

Rare Earth Element in Bivalves' Soft Tissues of French Metropolitan Coasts: Spatial and Temporal Distribution.

Rare earth elements (REE) are becoming an environmental pollutant of emerging concern, linked to their use in various anthropic processes. Because REE bioconcentrate in marine organisms throughout their food webs, a better understanding of biogeochemical processes leading to REE concentrations found in coastal species is necessary. This study was designed to assess REEs concentrations in various common bivalves from the French coastline to identify possible geographic, taxonomic, or temporal variations of concentrations. Based on the French Mussel Watch program, three species of bivalves (oyster Crassostrea gigas and mussels Mytilus edulis and Mytilus galloprovincialis) were collected all along the French metropolitan coast and soft tissues were analyzed for REE concentrations. Results have shown higher REE concentrations in bivalve soft tissues near estuaries without taxonomic nor national geographic differences. The highest levels have been observed in the Gironde estuary with total REE concentrations (∑REE) in oysters up to 10.94 µg g-1 d.w. The REE distribution pattern in both mussel species described a particle-like (inverse V-shape) pattern, whereas C. gigas REE distribution pattern changes from a particle-like to a dissolved-like pattern with a heavy REE (HREE) enrichment. However, no environmental parameter could be linked to these pattern changes. Finally, neither Gd anomalies nor an evolution of REE concentrations over a 30-year period have been detected in bivalves' soft tissues.

Impact of nickel mining in New Caledonia assessed by compositional data analysis of lichens.

The aim of this study is to explore the use of lichens as biomonitors of the impact of nickel mining and ore treatment on the atmosphere in the New Caledonian archipelago (South Pacific Ocean); both activities emitting also Co, Cr and possibly Fe. Metal contents were analysed in thirty-four epiphytic lichens, collected in the vicinity of the potential sources, and in places free from known historical mining. The highest Ni, Co, and Cr concentrations were, as expected, observed in lichens collected near ore deposits or treatment areas. The elemental composition in the lichens was explored by multivariate analysis, after appropriately transforming the variables (i.e. using compositional data analysis). The sample score of the first principal component (PC1) makes the largest (positive) multiplicative contribution to the log-ratios of metals originating from mining activities (Ni, Cr, Co) divided by Ti. The PC1 scores are used here as a surrogate of pollution levels related to mining and metallurgical activity. They can be viewed as synthetic indicators mapped to provide valuable information for the management and protection of ecosystems or, as a first step, to select locations where air filtration units could be installed, in the future, for air quality monitoring. However, as this approach drastically simplifies the problem, supplying a broadly efficient picture but little detail, recognizing the different sources of contamination may be difficult, more particularly when their chemical differences are subtle. It conveys only relative information: about ratios, not levels, and is therefore recommended as a preliminary step, in combination with close examination of raw concentration levels of lichens. Further validation using conventional air-monitoring by filter units should also prove beneficial.