Probabilistic ecotoxicological risk assessment of heavy metal and rare earth element mixtures in aquatic biota using the DGT technique in coastal sediments

Rare earth elements in seagrass beds: Contamination, bioaccumulation, and biomonitoring

Coastal environments are increasingly vulnerable to contamination from rare earth elements (REE) due to expanding anthropogenic activities, yet the fate and ecological risks of REE in ecologically critical seagrass ecosystems remain poorly understood. This study deciphered the behavior, fractionation, and compartmentalization of REE in both seagrass sediments and tissues. Total REE concentrations in sediments ranged from 70.5 to 258.8 mg kg-1, with Ce emerging as the most enriched REE in both matrices. Pollution Load Index varied from 0.7 to 3.0, indicating slight to moderate REE pollution, with localized enrichment of some REE (e.g., Tb, Lu) pointing to anthropogenic influences such as industrial effluents and marine traffic. Principal component and enrichment factor analyses attribute approximately 66 % of REE patterns to geogenic weathering, while 22.6 % reflect anthropogenic contributions. Geochemical partitioning revealed that Fe-Mn oxides serve as major REE sinks, while organic matter plays a dual role-enhancing total REE retention through complexation yet reducing mobility by stabilizing labile fractions. Correlations between REE concentrations in seagrass tissues and sediments suggest species-specific uptake and limited translocation. These findings underscore the capacity of seagrasses to serve as sensitive bioindicators for REE pollution and highlight the importance of organic matter and rhizosphere processes in modulating REE bioavailability.

Nutrients and metal(loid)s in surface sediments of the Chishui River: A DGT-based assessment of the last natural tributary of the upper Yangtze River (China)

This study investigates the distribution and probabilistic ecotoxicological risk assessment of nutrients and metal(loid)s in the Chishui River, the last natural tributary of the upper Yangtze River, which plays a crucial role in maintaining regional biodiversity and water quality. Understanding the impact of contaminants in this ecologically significant river is essential for effective environmental management. Sediment samples were analyzed using diffusive gradients in thin films (DGT) to measure labile concentrations of nutrients and metal(loid)s, revealing significant spatial variability. Concentrations of PO4-P, NH4-N, NO3-N, and metal(loid)s such as Mn, Fe, Cu, and Zn varied notably across sampling sites. Risk quotient (RQ) analysis identified Mn as posing the highest ecological risk, followed by Cu and Fe. A combined probabilistic risk assessment using the SPI (Species Sensitivity Distribution-Probabilistic Risk Assessment-Inclusion-Exclusion Principle) model indicated a 32.46 % probability of toxic effects from nutrient and metal(loid) mixtures on aquatic organisms. This study underscores the effectiveness of DGT technology in assessing bioavailable contaminants and highlights the need for targeted risk management strategies to mitigate ecological impacts in the Chishui River.

Enhancing sediment toxicity assessments: Integrating bioavailability metrics with sediment effect concentrations for improved predictive accuracy

Sediments act as both sinks and sources for contaminants, particularly heavy metals like cadmium (Cd), posing risks to aquatic ecosystems. To evaluate sediment toxicity, sediment quality guidelines (SQGs) such as Sediment Effect Concentrations (SECs) have been widely applied. However, these methods often fail to resolve toxicity in the "Uncertain" range, where contaminant concentrations approach threshold values. This limitation arises from the reliance on bulk sediment concentrations, which do not account for bioavailability. This study integrates bioavailability-focused evaluation using Interstitial Water Toxic Units (IWTU) with traditional SEC frameworks to enhance sediment toxicity assessments. Using SECs alone, the toxicity thresholds were 0.09 mg/kg for long-term ecological safety (Consensus Level 1) and 0.36 mg/kg for benthic communities (Consensus Level 2). However, predictability, defined as the ability to correctly classify sediments correctly based on bioassay results, was limited to 43 % due to ambiguity in the "grey area" between these thresholds. To address this, aqueous phase Cd concentrations, derived from a partitioning coefficient model, were normalized to the USEPA Final Chronic Value (FCV) of 0.72 μg/L to calculate IWTU values. This tiered approach integrates SECs with bioavailability-focused assessments, improving predictability to 76 % by refining classifications in the "Uncertain" category. The proposed framework effectively combines the ecological breadth of SECs with the precision of IWTU, addressing the limitations of single-method approaches. These findings underscore the importance of bioavailability-focused metrics in enhancing the reliability of sediment toxicity assessments and management practices.

Coastal redox shifts over the past 167 years and preservation of total organic carbon and total nitrogen

This study reconstructs the environmental history of Xincun Lagoon over the past 167 years using sediment core XCW, employing Cu/Zn as a proxy for redox changes. Time-series analysis of Cu/Zn ratios reveals a significant decline (linear regression slope = -0.00082, p < 0.001; Mann-Kendall τ = -0.601, p < 0.001), indicating a steady reduction in redox potential and oxygen levels throughout the study period. This trend is attributed to anthropogenic activities, eutrophication, and climate-induced changes. Additionally, correlation analysis highlights strong linear relationships between Cu/Zn ratios and both total organic carbon (TOC) and total nitrogen (TN), emphasizing the role of redox conditions in the preservation of TOC and TN in lagoon sediments. The study also identifies a shift in organic matter sources from predominantly marine to a mix of marine and terrestrial inputs after 1990. These findings offer new insights into the interplay between redox dynamics and sedimentary processes, advancing our understanding of the lagoon's environmental evolution.

The Bioaccumulation, Fractionation and Health Risk of Rare Earth Elements in Wild Fish of Guangzhou City, China

In this study, the total content of REEs ranged from 1.32 to 67.74 μg/kg, with a predominant presence of light REEs. The ΔEu and ΔCe values, which exceeded and approached 1, respectively, indicated positive Eu anomalies and low Ce anomalies. Wild fish were categorized into high-, medium-, and low-REEs-bioaccumulation groups using cluster analysis. Higher LRs/HRs and ΔEu values, coupled with lower ΔCe values, in fish from the high-bioaccumulation group suggested that increased bioaccumulation mitigated fractionation. Omnivorous fish with higher REEs levels and lower LRs/HRs indicated broader feeding sources may enhance REE bioaccumulation and diminish fractionation. Elevated REEs concentrations and LRs/HRs in demersal fish highlighted a preferential accumulation of light REEs in the benthic environment. Smaller fish with higher REEs levels but lower LRs/HRs were likely associated with complex feeding sources. Regression analysis revealed that fish with lengths and weights of less than 18 cm and 130 g, respectively, were more susceptible to REEs bioaccumulation. Despite higher ADI values indicating a greater risk for children and Pelteobagrus fulvidraco, all ADI values within 70 μg/(kg·d) suggested that fish consumption poses no risk. This study confirmed that the fractionation of REEs in fish can be used to trace their bioconversion.

Potential Toxicity of Nine Rare Earth Elements (REEs) on Marine Copepod Tigriopus fulvus

The present study focused, for the first time, on the adverse effects of nine REEs on the marine copepod Tigriopus fulvus. For this purpose, copepod mortality, immobilization, and naupliar development were assessed. Overall, the results demonstrated that all REEs tested exerted significant adverse effects on T. fulvus, with LC50 values ranging from 0.56 to 1.99 mg/L. Concentration-dependent increases in mortality and immobilization for all tested REEs were observed. Following exposure of nauplii to REEs, a significant slowing of nauplii development was shown with all REEs tested. The results obtained clearly highlight the potential toxicity of REEs, and, in particular, of Lanthanum, which could have consequences on the survival and development of T. fulvus, affecting the copepod population.

Potentially toxic elements in surface sediments of the Beibu Gulf, South Sea, China: Occurrence, bioavailability and probabilistic risk assessment

At present, pollution of gulf sediments with potentially toxic elements (PTEs) has become a prominent marine environmental problem. This study thoroughly investigated the occurrence, bioavailability, and probabilistic risk of PTEs in the surface sediments of the Beibu Gulf. The average total concentrations (mg/kg) were 8.03 for As, 0.06 for Cd, 52.73 for Cr, 9.86 for Cu, 0.04 for Hg, 18.70 for Ni, 27.77 for Pb and 59.80 for Zn, respectively. The positive matrix factorization model revealed that the PTE enrichment was primarily due to composite sources from aquaculture and fisheries activities, industrial and agricultural sources. Risk assessment code and correlation analysis indicated that Cd had the highest bioavailability, influenced by TOC and TP. The probabilistic risk assessment model estimated a 60.83 % probability that the mixed PTEs in the Beibu Gulf's surface sediments could have toxic effects on aquatic life. These findings underscore the impact of intensive human activities on PTE pollution and highlight the need for further research on PTE ecotoxicology and pollution control strategies.

Toxicity of rare earth elements (REEs) to marine organisms: Using species sensitivity distributions to establish water quality guidelines for protecting marine life

A lack of chronic rare earth element (REE) toxicity data for marine organisms has impeded the establishment of numerical REE water quality benchmarks (e.g., guidelines) to protect marine life and assess ecological risk. This study determined the chronic no (significant) effect concentrations (N(S)ECs) and median-effect concentrations (EC50s) of eight key REEs (yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), gadolinium (Gd), dysprosium (Dy) and lutetium (Lu)) for 30 coastal marine organisms (encompassing 22 phyla and five trophic levels from temperate and tropical habitats). Organisms with calcifying life stages were most vulnerable to REEs, which competitively inhibit calcium uptake. The most sensitive organism was a sea urchin, with N(S)ECs ranging from 0.64 μg/L for Y to 1.9 μg/L for La and Pr, and EC50s ranging from 4.3 μg/L for Y to 14.4 μg/L for Pr. Conversely, the least sensitive organism was a cyanobacterium, with N(S)ECs ranging from 121 μg/L for Y to 469 μg/L for Pr, and EC50s ranging from 889 μg/L for Y to 3000 μg/L for Pr. Median sensitivity varied 215-fold across all organisms. The two-fold difference in median toxicity (μmol/L EC50) among REEs (Y ∼ Gd > Lu ∼ Nd ∼ Dy ∼ Ce > La ∼ Pr) was attributed to offset differences in binding affinity (log K) to cell surface receptors and the percentage of free metal ion (REE3+) in the test waters. The toxicity (EC50) of the remaining REEs (samarium, europium, terbium, holmium, thulium and ytterbium) was predicted using a combination of physicochemical data and measured EC50s for the eight tested REEs, with good agreement between predicted and measured EC50s for selected organisms. Numerical REE water quality guidelines to protect marine life were established using species sensitivity distributions (e.g., for 95 % species protection, values ranged from 1.1 μg/L for Y to 3.0 μg/L for La, Pr or Lu).

Utilizing machine learning to evaluate heavy metal pollution in the world's largest mangrove forest

The world's largest mangrove forest (Sundarbans) is facing an imminent threat from heavy metal pollution, posing grave ecological and human health risks. Developing an accurate predictive model for heavy metal content in this area has been challenging. In this study, we used machine learning techniques to model sediment pollution by heavy metals in this vital ecosystem. We collected 199 standardized sediment samples to predict the accumulation of eleven heavy metals using ten different machine learning algorithms. Among them, the extremely randomized tree model exhibited the best performance in predicting Fe (0.87), Cr (0.89), Zn (0.85), Ni (0.83), Cu (0.87), Co (0.62), As (0.68), and V (0.90), achieving notable R2 values. On the other hand, the random forest outperformed for predicting Cd (0.72) and Mn (0.91), whereas the decision tree model showed the best performance for Pb (0.73). The feature attribute analysis identified FeV, CrV, CuZn, CoMn, PbCd, and AsCd relationships resembled with correlation coefficients among them. Based on the established models, the prediction of the contamination factor of metals in sediments showed very high Cd contamination (CF ≥ 6). The Moran's I index for Cd, Cr, Pb, and As were 0.71, 0.81, 0.71, and 0.67, respectively, indicating strong positive spatial autocorrelation and suggesting clustering of similar contamination levels. Conclusively, this research provides a comprehensive framework for predicting heavy metal sediment pollution in the Sundarbans, identifying key areas needing urgent conservation. Our findings support the adoption of integrated management strategies and targeted remedial actions to mitigate the harmful effects of heavy metal contamination in this vital ecosystem.

Trophic dilution of rare earth elements along the food chain of the Seine estuary (France)

Society's interest in rare earth elements (REEs) and their increasing use in many fields is leading to enrichments in aquatic environments, such as estuaries. This study of the Seine estuary assessed the distribution of REEs along the food web, including different species from 5 phyla representing different trophic levels. Total REE concentrations, which were higher in algae, mollusks, crustaceans and annelids (4.85-156; 1.59-4.08; 2.48 ± 1.80 and 0.14 ± 0.11 μg/g dw, respectively) than in vertebrates (0.03-0.15 μg/g dw), correlated with δ15N indicated a trophic dilution. REE contributions in the studied species were higher for light REEs than for heavy and medium REEs. Positives anomalies for Eu, Gd, Tb and Lu were highlighted particularly in vertebrates, possibly due to species-dependent bioaccumulation/detoxification or related to anthropogenic inputs. The calculated BAF and BSAF indicated an important partitioning of REEs in organisms compared to the dissolved phase and a limited transfer from sediment to organisms.

Comparison of sediment bioavailable methods to assess the potential risk of metal(loid)s for river ecosystems

A heavily impacted river basin (Caudal River, NW Spain) by Hg and Cu mining activities, abandoned decades ago, was used to evaluate the environmental quality of their river sediments. The obtained results compared with reference values established by the US EPA and the Canadian Council of Ministers of the Environment for river sediments, have shown that the main elements of environmental concern are arsenic (As), mercury (Hg) and, to a lesser extent, copper (Cu), which reach concentrations up to 1080, 80 and 54 mg kg-1, respectively. To understand the role that river sediments play in terms of risk to ecosystem health, a comparison has been made between the total content of metal(oid)s in the sediments and the bioavailable contents of the same elements in pore water, passive DGT (Diffusive Gradients in Thin films) samplers and the sediment extractant using acetic acid. A good correlation between the As and Cu contents in the DGTs and the pore water was found, resulting in a transfer from the pore water to the DGT of at least 47 % of the Cu and more than 75 % of the As when the concentrations were low, with a deployment time of 4 days. When As and Cu concentrations were higher, their transfer was not so high (above 23.6 % for As and 19.3 % for Cu). The transfer of Hg from the pore water to the DGT was practically nil and does not seem to depend on the content of this metal. The fraction extracted with acetic acid, conventionally accepted as bioavailable, was clearly lower than that captured by DGTs for As and Cu (≤5 % and ≤8.5 % of the total amount, respectively), while it was similar for Hg (0.2 %).

Controlling factors and sources-specific ecological risks associated with toxic metals in core sediments from cascade reservoirs in Southwest China

Toxic metals (TMs) in reservoir sediments pose significant risks to ecosystem security and human safety, yet their presence in the cascade reservoirs of the Lancang River remains understudied. This research examined TMs in core sediments from the Manwan (MW) and Dachaoshan (DCS) cascade reservoirs, aiming to elucidate contamination characteristics, controlling factors, and source-specific ecological risks. The study revealed that the concentrations of As, Cd, Cr, Cu, Hg, Ni, and Zn in the MW Reservoir (37.3, 0.54, 95.1, 44.0, 0.09, 44.8, and 135.7 mg/kg) were notably higher compared to the DCS Reservoir (14.6, 0.30, 82.6, 31.0, 0.08, 36.6, and 108.7 mg/kg). While both reservoirs demonstrated elevated contamination levels of Cd and Hg, the MW Reservoir also exhibited high levels of As, whereas the DCS Reservoir showed relatively high levels of Pb. Mining activities in upstream metal deposits significantly correlated Cd, Hg, and Zn in the MW Reservoir with sulfur. In both reservoir sediments, Cr and Ni displayed a greater affinity for iron oxides, while As, Cd, Cu, Hg, and Zn showed more affinity with manganese oxides. Ecological risk index (RI) values in half of the sediments from the MW Reservoir ranged from 300 to 600, denoting a significant ecological risk. Conversely, in the DCS Reservoir, 93.3 % of the sediments exhibited RI values between 150 and 300, signifying a moderate ecological risk. Source-oriented ecological risks highlighted the need for particular attention to Cd from anthropogenic sources in the MW Reservoir. These findings underscore the importance of implementing measures for TM contamination prevention and control, contributing to strategic planning for sustainable water resource management in the Lancang-Mekong River.

Environmental and dietary exposure to 24 polycyclic aromatic hydrocarbons in a typical Chinese coking plant

Polycyclic aromatic hydrocarbons (PAHs), known for their health risks, are prevalent in the environment, with the coking industry being a major source of their emissions. To bridge the knowledge gap concerning the relationship between environmental and dietary PAH exposure, we explore this complex interplay by investigating the dietary exposure characteristics of 24 PAHs within a typical Chinese coking plant and their association with environmental pollution. Our research revealed Nap and Fle as primary dietary contaminants, emphasizing the significant influence of soil and atmospheric pollution on PAH exposure. We subjected our data to non-metric multidimensional scaling (NMDS), Spearman correlation analysis, Lasso regression, and Weighted Quantile Sum (WQS) regression to delve into this multifaceted phenomenon. NMDS reveals that dietary PAH exposure, especially within the high molecular weight (HMW) group, is common both within and around the coking plant. This suggests that meals prepared within the plant may be contaminated, posing health risks to coking plant workers. Furthermore, our assessment of dietary exposure risk highlights Nap and Fle as the primary dietary contaminants, with BaP and DahA raising concerns due to their higher carcinogenic potential. Our findings indicate that dietary exposure often exceeds acceptable limits, particularly for coking plant workers. Correlation analyses uncover the dominant roles of soil and atmospheric pollution in shaping dietary PAH exposure. Soil contamination significantly impacts specific PAHs, while atmospheric pollution contributes to others. Additionally, WQS regression emphasizes the substantial influence of soil and drinking water on dietary PAHs. In summary, our study sheds light on the dietary exposure characteristics of PAHs in a typical Chinese coking plant and their intricate interplay with environmental factors. These findings underscore the need for comprehensive strategies to mitigate PAH exposure so as to safeguard both human health and the environment in affected regions.

Fate, subcellular distribution and biological effects of rare earth elements in a freshwater bivalve under complex exposure

Rare earth elements (REE) are emerging contaminants due to their increased use in diverse applications including cutting-edge and green-technologies. Their environmental concerns and contradicting results concerning their biological effects require an extensive understanding of REE ecotoxicology. Thus, we have studied the fate, bioaccumulation and biological effects of three representative REE, neodymium (Nd), gadolinium (Gd) and ytterbium (Yb), individually and in mixture, using the freshwater bivalve Corbicula fluminea. The organisms were exposed for 96 h at 1 mg L-1 REE in the absence and presence of dissolved organic matter (DOM) reproducing an environmental contamination. Combined analysis of the fate, distribution and effects of REE at tissue and subcellular levels allowed a comprehensive understanding of their behaviour, which would help improving their environmental risk assessment. The bivalves accumulated significant concentrations of Nd, Gd and Yb, which were decreased in the presence of DOM likely due to the formation of REE-DOM complexes that reduced REE bioavailability. The accumulation of Nd, Gd and Yb differed between tissues, with gills > digestive gland ≥ rest of soft tissues > hemolymph. In the gills and in the digestive gland, Nd, Gd and Yb were mostly (>90 %) distributed among metal sensitive organelles, cellular debris and detoxified metal-rich granules. Gadolinium, Yb and especially Nd decreased lysosome size in the digestive gland and disturbed osmo- and iono-regulation of C. fluminea by decreasing Na concentrations in the hemolymph and Ca2+ ATPase activity in the gills. Individual and mixed Nd, Gd and Yb exhibited numerous similarities and some differences in terms of fate, accumulation and biological effects, possibly because they have common abiotic and biotic ligands but different affinities for the latter. In most cases, individual and mixed effects of Nd, Gd, Yb were similar suggesting that additivity approach is suitable for the environmental risk assessment of REE mixtures.

Rare earth elements in sediments from a representative Chinese mariculture bay: Characterization, DGT-based bioaccessibility, and probabilistic ecological risk

Rare earth elements (REEs) are emerging contaminants due to their worldwide exploitation in the high-technology sector. Aquaculture systems, particularly those located within coastal areas, are fragile ecosystems due to anthropogenic impacts regarding urban and aquaculture activities. However, to date, there are no reports on the combined toxicity of rare earth element (REE) mixtures on aquatic biota in sediments from coastal aquaculture systems. In this study, the combined toxicity of REE mixtures based on probabilistic risk assessment indicated that the surface sediments of Zhelin Bay had a 1.86% probability of toxic effects on aquatic biota. The average value of total REEs (TREEs) was 297.37 μg/g, with light REEs representing the major part. A factor analysis (FA)-geographic information system (GIS)-based approach coupled with correlation analysis (CA) revealed that the REEs are derived from anthropogenic sources through fluvial processes.