Nonmetric multidimensional scaling and probabilistic ecological risk assessment of trace metals in surface sediments of Daya Bay (China) using diffusive gradients in thin films

In situ high-resolution insights into the dynamics of arsenic (As) species and heavy metals across the sediment-water interface in a deep karst reservoir

Arsenic (As) and heavy metal contamination in aquatic systems pose critical environmental challenges, particularly in reservoirs. This study utilized dual-sided high-resolution diffusive gradients in thin films (DGT) probes on-site to investigate the spatial distribution and mobility of As species and heavy metals (Cd, Cr, Cu, Ni, Pb, Sb, and Zn) in the Hongfeng Reservoir, a deep karst reservoir in southwest China. Results revealed that As mobility was primarily governed by redox-sensitive processes, including the reduction of As(V) to As(III) and the reductive dissolution of Fe/Mn oxides. As(III) dominated porewater under reducing conditions, while As(V) was prevalent in overlying water under oxidative environments. Sulfate reduction significantly influenced As mobility, and competitive adsorption with P enhanced As release in eutrophic conditions. Heavy metals exhibited distinct spatial profiles and inter-element correlations, shaped by redox variability. Flux analysis identified sediments as sources for As, Fe, Mn, P, and S, and as sinks for most heavy metals. As(III) fluxes in the North Central reflected strong reducing conditions, while As(V) fluxes in the South Central highlighted localized oxidative processes. These findings offer valuable insights into geochemical processes in karst reservoirs, aiding in the understanding of contaminant dynamics and providing guidance for managing sediment pollution and protecting water quality.

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.

Sediment heavy metal speciation of Hirakud Reservoir-a Ramsar site in Mahanadi River in India

Heavy metal speciation is an important tool for the assessment of sediment quality. This work was conducted to investigate the geochemical occurrence, distribution, and spatial variability of sediment heavy metals in the Hirakud Reservoir (a Ramsar site) of the Mahanadi River in India. Estimation based on a single-extraction (speciation) method revealed the dominance of Fe-Mn-bound (39.33%) fractions suggesting the potential mobility of heavy metals. Co-dominance of residual (35.03%) and organic matter-sulfide (23.02%) fractions indicate lattice-bound associations of elements under natural conditions and suggest anthropogenic organic input contribution respectively. The heavy metals distribution was spatially affected (p < 0.05). While, Ag, Cd, Hg, and Mo displayed extremely severe enrichment (EF > 50) and very strong geo-accumulation conditions (Igeo > 5); Cd and Hg displayed very high ecological risk (ERF > 320). However, the contamination factor for all heavy metals except Cd and Hg showcased low contamination (CF < 1). The principal component and cluster analysis revealed that the source of Mn, Mo, Hg, and Ag was mainly from anthropogenic or biogenic origin. The Fe and Al however displayed signs of being derived from multiple sources. However, the risk assessment code (RAC) results suggest that As exhibited a medium to very high risk (11 < RAC < 30) of bio-availability. Thus, the results of this study can be used for the formulation of strategies for the reduction of anthropogenic loads, planning for sediment quality management, and regular monitoring to curb the rising pollution issues of the reservoir.

Tracing sources-oriented ecological risks of metal(loid)s in sediments of anthropogenically-affected coastal ecosystem from northeast bay of Bengal

The current study focused on thirty-nine locations in the four islands (i.e., St. Martin, Moheskhali, Kutubdia, and Sonadia) and beach (Innani Beach) along the northeast Bay of Bengal to quantify sources-orientated ecological risks of metal(loid)s. The mean concentrations of As, Mn, Cr, Cd, and Pb are 4.8, 8.7, 1.6, 1.1, and 2 times higher than average shale volume (ASV) values. Key findings revealed that Mn, Cr, Cd, Pb, and As exceed safe levels, particularly on St. Martin and Moheshkhali islands, where tourism and coal mining intensify contamination. Ecological indexes showed moderate to considerable contamination levels, suggesting diverse impacts on aquatic life. Positive matrix factorization (PMF) model-based Nemerow integrated risk index (NIRI) indicated that mixed and coal mining sources posed a moderate risk for 10.26 % and 5.13 % of sediment samples, respectively. This paper serves as a model-based plan for mitigating pollution risks of metal(oid)s in coastal sediments on the northeast coast.

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.

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 %).

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.

Advances in identifying and managing emerging contaminants in aquatic ecosystems: Analytical approaches, toxicity assessment, transformation pathways, environmental fate, and remediation strategies

Emerging contaminants (ECs) are increasingly recognized as threats to human health and ecosystems. This review evaluates advanced analytical methods, particularly mass spectrometry, for detecting ECs and understanding their toxicity, transformation pathways, and environmental distribution. Our findings underscore the reliability of current techniques and the potential of upcoming methods. The adverse effects of ECs on aquatic life necessitate both in vitro and in vivo toxicity assessments. Evaluating the distribution and degradation of ECs reveals that they undergo physical, chemical, and biological transformations. Remediation strategies such as advanced oxidation, adsorption, and membrane bioreactors effectively treat EC-contaminated waters, with combinations of these techniques showing the highest efficacy. To minimize the impact of ECs, a proactive approach involving monitoring, regulations, and public education is vital. Future research should prioritize the refining of detection methods and formulation of robust policies for EC management.

Anthropogenic influences on the sources and distribution of organic carbon, black carbon, and heavy metals in Daya Bay's surface sediments

The total organic carbon (TOC), total nitrogen (TN), black carbon (BC), δ13CTOC, δ15N, δ13CBC, grain size, and heavy metals of surface sediments collected from Daya Bay were determined to investigate the spatial distributions of these parameters and to evaluate the influences of human activities. Marine organic matter was found to constitute approximately 84.41 ± 7.70 % of these sediments on average. The western and northern regions of Daya Bay exhibited relatively fine grain sizes, weak hydrodynamic conditions, and high sedimentation rates, which favored the burial and preservation of organic matter. The high concentration of organic matter could be attributed to the influence of petroleum and aquaculture industries. Fossil fuels were the main source of BC. The enrichment factor (EF) and geo-accumulation index (Igeo) were used to evaluate the sources and pollution levels of heavy metals. The results revealed that the source and distribution of heavy metals were strongly influenced by human activities, resulting in moderate pollution levels across most regions of Daya Bay. A strong correlation was observed between the Igeo values of heavy metals and BC, TOC, TN, and mean particle grain size (Mz). This suggests that the ability of sediments in Daya Bay to enrich and adsorb heavy metals depends on the sediment grain size, the content and type of organic matter. Importantly, sediments in the inner bay of Daya Bay exhibited a greater capacity to impede the migration of heavy metals compared to those in the outer bay.

Bioenrichment preference and human risk assessment of arsenic and metals in wild marine organisms from Dapeng (Mirs) Bay, South China Sea

Bioenrichment preference of arsenic and metals in wild marine organisms has been scarcely considered. Twenty species including fishes, cephalopods, crustaceans, and bivalve mollusks were collected from Dapeng (Mis) Bay and analyzed for arsenic and metals. Through this study, we had obtained the following four main conclusions: (1) average concentrations of arsenic and metals (μg/kg, wet weight) in the aquatic organism samples were 48.7 for Cr, 1762.0 for Mn, 20,632.8 for Fe, 33.0 for Co, 119.5 for Ni, 3184.7 for Cu, 12,040.5 for Zn, 389.0 for As, 189.1 for Se, 144.4 for Cd, 15.0 for Hg, and 55.3 for Pb; (2) factor analysis (FA) revealed that the studied twenty species exhibited three types of arsenic and metal bioenrichment preference;(3) non-carcinogenic health risk assessment indicated insignificant health effects from marine organism consumption; (4) carcinogenic health risk assessment revealed an unacceptable risk from consumption of nine species, seven of which were crustaceans.

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

Heavy metals (HMs) are routine contaminants due to their extensive use worldwide. Rare earth elements (REEs) are emerging contaminants because of their global exploitation for use in the high-tech sector. Diffusive gradients in thin films (DGT) are an effective method for measuring the bioavailable component of pollutants. This study represents the first assessment of the mixture toxicity of HMs and REEs in aquatic biota using the DGT technique in sediments. Xincun Lagoon was chosen as the case study site because it has been contaminated by pollutants. Nonmetric multidimensional scaling (NMS) analysis reveals that a wide variety of pollutants (Cd, Pb, Ni, Cu, InHg, Co, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Ho, Er, Tm, and Yb) are primarily impacted by sediment characteristics. Appraisal of single HM-REE toxicity reveals that the risk quotient (RQ) values for Y, Yb and Ce notably exceeded 1, demonstrating that the adverse effects of these single HMs and REEs should not be ignored. The combined toxicity of HM-REE mixtures in terms of probabilistic ecological risk assessment shows that the Xincun surface sediments had a medium probability (31.29%) of toxic effects on aquatic biota.

Heavy metals in riverine/estuarine sediments from an aquaculture wetland in metropolitan areas, China: Characterization, bioavailability and probabilistic ecological risk

Aquaculture wetlands, particularly those located within urban areas, are fragile ecosystems due to urban and aquaculture impacts. However, to date, there are no reports on the combined toxicity of heavy metal mixtures in aquatic biota in sediments from aquaculture wetlands in metropolitan areas. Thus, the characterization, bioavailability, and ecological probability risk of heavy metals were studied in the riverine/estuarine sediments of the Rongjiang River in an aquaculture wetland in Chaoshan metropolis, South China. In the study area, the average total concentrations (mg/kg) were 2.38 (Cd), 113.40 (Pb), 88.27 (Cr), 148.25 (Ni), 62.08 (Cu), 125.18 (Zn), 45,636.44 (Fe), and 797.18 (Mn), with the Cd pollution being regarded as extremely serious based on the enrichment factor (EF). There are two main sources of heavy metals in the study area; Ni, Pb, Zn, Fe and Mn are mainly from domestic waste, while Cr, Cd and Cu are possibly associated with industrial production activities. The bioavailability of most heavy metals accounted for more than 20% of the total concentration. The combined toxicity of heavy metal mixtures based on probabilistic risk assessment suggests that the surface sediments of the Rongjiang River and its estuary had a 15.71% probability of toxic effects on aquatic biota.

GIS-based approach and multivariate statistical analysis for identifying sources of heavy metals in marine sediments from the coast of Hong Kong

Hong Kong is an urbanized coastal city which experiences substantially different metal loads from anthropogenic activities. This study was aimed at analyzing the spatial distribution and pollution evaluation of ten selected heavy metals (As, Cd, Cr, Cu, Pb, Hg, Ni, Zn, Fe, V) in the coastal sediments of Hong Kong. The distribution of heavy metal pollution in sediments has been analyzed using the geographic information system (GIS) technique, and their pollution degrees, corresponding potential ecological risks and source identifications, have been studied by applying the enrichment factor (EF) analysis, contamination factor (CF) analysis, potential ecological risk index (PEI), and integrated multivariate statistical methods, respectively. Firstly, the GIS technique was used to access the spatial distribution of the heavy metals; the result revealed that pollution trend of these metals was decreased from the inner to the outer coast sites of the studied area. Secondly, combining the EF analysis and CF analysis, we found that the pollution degree of heavy metals followed the order of Cu > Cr > Cd > Zn > Pb > Hg > Ni > Fe > As > V. Thirdly, the PERI calculations showed that Cd, Hg, and Cu were the most potential ecological risk factors compared to other metals. Finally, cluster analysis combined with principal component analysis showed that Cr, Cu, Hg, and Ni might originate from the industrial discharges and shipping activities. V, As, and Fe were mainly derived from the natural origin, whereas Cd, Pb, and Zn were identified from the municipal discharges and industrial wastewater. In conclusion, this work should be helpful in the establishment of strategies for contamination control and optimization of industrial structures in Hong Kong.

Distribution, Multi-Index Assessment, and Sources of Heavy Metals in Surface Sediments of Zhelin Bay, a Typical Mariculture Area in Southern China

The occurrence, multi-index assessment, and sources of heavy metals in surface sediments of Zhelin Bay were investigated. Average heavy metal concentrations (mg/kg) were 81.89 (Cr), 770.76 (Mn), 16.81 (Co), 62.25 (Ni), 96.30 (Cu), 162.04 (Zn), and 73.40 (Pb), with the concentrations of studied seven heavy metals being significantly higher than their corresponding background values. Geo-accumulation index (I_geo) and pollution load index (PLI) were implemented to assess degree of heavy metal contamination. The I_geo and PLI indicated that Cr, Mn, Co, Zn, and Pb were slightly polluted, and Cu and Ni were moderately polluted in the region. Potential ecological risk index (RI) and mean possible effect level (PEL) quotient were conducted to assess ecological risk. The RI and mean PEL quotient demonstrated that surface sediments of Zhelin Bay were slight ecological risks and exhibited a 21% probability of toxicity. Principal component analysis (PCA) combined with the correlation analysis (CA) and hierarchical cluster analysis (HAC) revealed that the heavy metal contamination in Zhelin Bay might originate from three type sources.