Chemical and physiological metal bioaccessibility assessment in surface bottom sediments from the Deba River urban catchment: Harmonization of PBET, TCLP and BCR sequential extraction methods

Evaluation of the buffer-blocking capacity of acrocarpous moss Campylopus schmidii as candidate for copper and cadmium migration

This study evaluates the ability of Campylopus schmidii to inhibit the horizontal migration of copper and cadmium under simulated acid rain conditions. Experiments at varying pH levels (3.6, 4.7, and 5.6) revealed significant reductions in copper and cadmium migration rates, especially at pH 3.6, where concentrations dropped to 3.68% and 30.98% of those in exposed soil after 90 days. No leachate residue was collected from moss-covered groups, indicating effective soil and water loss control. Transcriptome analysis identified numerous differentially expressed genes under cadmium stress, highlighting enriched pathways related to cell structure, signaling, and metabolism, demonstrating Campylopus schmidii 's complex molecular mechanisms for heavy metal stress adaptation. These findings underscore the potential of Campylopus schmidii for environmental restoration and pollution control in mining areas.

Magnetic response and bioaccessibility of toxic metal pollution in outdoor dustfall in Shanghai, China

Toxic metal content testing, environmental magnetic monitoring and in vitro bioaccessibility experiments each have their own advantages and are often used independently for environmental monitoring, but there are few studies that combine the three to evaluate the hazards of toxic metals to humans. This paper investigated the total content, magnetic properties and bioaccessibility of nine potentially toxic metal elements (Zn, Sn, Pb, Cu, Fe, Ni, Cr, Sr, Mn) in dustfall from different functional zones in Shanghai, China, and systematically compared the related results. The results show that these nine metal elements have different degrees of contamination and enrichment in outdoor dustfall, and their content distribution shows the following trend: Zn > Sn > Pb > Cu > Fe > Ni > Cr > Sr > Mn. Magnetic characteristics χlf and SIRM are mostly positively correlated with the metal elements, indicating that the higher the content of magnetic minerals in the sample, the higher the concentration of metal elements. It was also found that χlf, SIRM, and χARM can well reflect the characteristics of dustfall pollution. The magnetic minerals have a certain degree of enrichment, and the particle size of the magnetic minerals is relatively coarse, mainly in the form of coarse multi-domain and pseudo-single-domain particles, which are largely derived from anthropogenic pollution. The χlf and PM10 concentrations in the precipitation show relatively similar spatial trends, so χlf, SIRM, and χARM can be used as air pollution indices to facilitate the evaluation of metal elements pollution in dustfall. The overall trend in gastric bioaccessibility is Pb > Zn > Mn > Cu > Cr. Due to the increase in the pH of digestive fluid, the bioavailability of toxic metals decreases significantly from the gastric stage to the intestinal stage. χlf, SIRM, and χARM/SIRM are all related to the bioaccessibility of toxic metals in the intestinal stage, so they can be used as toxicity indicators to evaluate the bioaccessibility of toxic metals in dustfall.

Digestive fluid components affect speciation and bioaccessibility and the subsequent exposure risk of soil chromium from stomach to intestinal phase in in-vitro gastrointestinal digestion

The simulated in-vitro gastrointestinal method provides a simple way to evaluate the health risk of human body exposed to soil contaminants. Several in-vitro methods have been successfully established for soil As, Pb, and Cd. However, the method development for soil Cr failed up to now, which could be resulted from alteration in the species of Cr (e.g., Cr(VI)/Cr(III)) caused by the gastrointestinal digestion components, ultimately affecting the accessibility of Cr. This study explored the transformation and bioaccessibility of Cr in two Cr-contaminated soils during the physiologically based extraction test. The water-soluble and exchangeable Cr in soil was dissolved in gastrointestinal tract, accompanied with reduction of Cr(VI) into Cr(III), and the reduction occurred after the chemical extraction in two soils rather than during the extraction. Pepsin and organic acids in gastric phase could reduce Cr(VI) into Cr(III) and reduction efficiency were 20.4%- 53.0%, while in intestinal phase, pancreatin and bile salt had little effect on the Cr(VI) reduction, instead, more Cr(VI) was released from soil. In the gastric solution, Cr(VI) was mainly present as HCrO4- and Cr(III) as free Cr3+ ion. In the intestinal phase, Cr(VI) mainly occurred as CrO42- and Cr(III) as Cr(OH)3 (aq). Cr in the soil solid phase was dominated as the precipitates of Cr-Fe oxide, which was hardly extracted. Bioaccessibility of Cr in gastric phase increased as extraction duration increased and decreased in the intestinal phase, the contrary trend was observed for the hazard quotient of Cr in two phases due to Cr(VI)/Cr(III) transformation. This study indicates that the gastrointestinal components could influence the Cr transformation and subsequently affect the Cr bioaccessibility, which would help for a successful establishment of in vitro determination method for soil Cr bioaccessibility.

Geochemical fractionation, bioaccessibility and ecological risk of metallic elements in the weathering profiles of typical skarn-type copper tailings from Tongling, China

Nonferrous metal tailings have long posed a significant threat to the surrounding environment and population. Previous studies have primarily focused on heavy metal pollution in the vicinity of sulfide tailings, while little attention was given to metal mobility and bioavailability within skarn-type tailings profile during weathering. Therefore, this study aimed to investigate the fractionation, bioaccessibility, and ecological risk associated with metallic elements (MEs, including Pb, Cd, Cr, Zn, and Cu) in two representative weathering copper-tailings profiles of Tongling mine (China). This was achieved through the use of mineralogical analyses, BCR extractions (F1: exchangeable, F2: reducible, F3: oxidizable, F4: residual fraction), in-vitro gastrointestinal simulation test (PBET) and risk assessment models. The mineral compositions of two weathering profiles were similar, with quartz and calcite being the dominant minerals, along with minor amounts of siderite, hematite and spangolite. The mean concentration in the tailings profile was approximately 0.31 (Cr), 1.8 (Pb), 12 (Zn), 33 (Cd) or 34 (Cu) times of the local background values (LBVs). The mean content of the bottom weakly-weathering layer in profile was about 0.36 (Cr), 0.91 (Pb), 1.91 (Cd), 2.73 (Zn) or 2.68 (Cu) times of the surface oxide layer, indicating a strong weathering-leaching effect. The average proportion of BCR-F1 fraction for Cd (30.94 %) was the highest among the five MEs, possibly due to its association with calcite. The PBET-extracted fractions for Cd, Zn and Cu were significantly positively correlated with the F1, F2 and F3 fractions of BCR, suggesting that these elements have higher bioavailability/bioaccessibility. The assessment results indicated that Cd posed a higher health risk, while the risk of Cu, Zn, and Pb is relatively low and Cr is safe. In conclusion, this study provides valuable insights into the environmental geochemical behavior and potential risks of MEs in skarn-type non-ferrous metal tailings ponds.

Bioaccessibility of arsenic, lead, and cadmium in contaminated mining/smelting soils: Assessment, modeling, and application for soil environment criteria derivation

Soil environment criteria (SEC) are commonly derived from the total concentration of pollutants in soils, resulting in overly stringent values. Herein, we examined the feasibility of deriving the SEC by using the bioaccessibility of pollutants. In this regard, soil samples from 33 locations at 12 mining/smelting sites in China were collected and examined in terms of soil properties, chemical fraction distributions, and bioaccessibilities of cadmium (Cd), lead (Pb), and arsenic (As). The gastric (GP) and intestinal phases (IP) of the potentially hazardous trace elements (PHEs) were measured by in vitro assays, showing that these values varied from 11 % to 72 %, 1-79 %, and 2-27 % for Cd, Pb and As, respectively. Pearson analysis showed that the GP and IP bioaccessibilities of these PHEs were mainly influenced by soil pH, CEC, and clay fraction and positively correlated with the sequential extraction form. The random forest regression (RF) model showed excellent performance in predicting the gastric phase (GP) bioaccessibilities of Cd, Pb, and As, with a mean R2 and RMSE of 0.86 and 0.31, respectively. Both the measured and predicted bioaccessibilities were feasible to be used to derive SEC. This work will contribute to the development of regional soil environmental standards based on bioaccessibility for Cd-, Pb-, and As-contaminated mining/smelting soils.

Assessing the environmental risk and mobility of cobalt in sediment near nonferrous metal mines with risk assessment indexes and the diffusive gradients in thin films (DGT) technique

The Jialing River is the tributary of the Yangtze River with the largest drainage area. In recent years, the Jialing River has suffered a series of environmental problems, such as discharge of industrial effluent and sand mining activities, which have severely threatened the aquatic ecosystem of the river. In the present study, we employed risk assessment indexes, sequential extraction and the diffusive gradients in thin films (DGT) technique to assess environmental risks and study the remobilization of cobalt (Co) in sediments. The potential ecological risk index and risk assessment code results demonstrated that Co may pose a low environmental and ecological risk to the local aquatic environment. However, BCR sequential extraction showed that the sum of the F1, F2 and F3 fractions of Co still accounted for over 50% of the Co in the study areas, indicating that sediments may be a source of Co release. The DGT results showed an increasing trend for DGT-labile Co in deep sediments (-8 cm to -12 cm), and the calculated flux values ranged from 0.08 to 15.54 ng cm²·day^-1, indicating that Co tends to transfer across the sediment-water interface at all sampling sites. Correlation analysis showed that F1-Co, F2-Co and F3-Co are the fractions readily captured by DGT and can be used for predicting Co remobilization in sediment. Sand mining activities contribute substantially to the release of Co from the F1 and F3 fractions as a result of strong stirring of sediments and introduction of oxygen into the sediments. The reductive dissolution of iron (Fe) and manganese (Mn) hydroxides or oxides causes the release of Co and Fe/Mn in the sediment, which leads to Co release from the reducible fraction. The above work suggests that sand mining in the Jialing River should be reasonably regulated to prohibit illegal sand mining activities.

Cadmium immobilization in lake sediment using different crystallographic manganese oxides: Performance and mechanism

Cd pollution in sediments poses severe threats to environmental safety and human health. Mn oxides have potential merit for the remediation of Cd pollution in sediment but have not received enough attention. Although Mn oxides have proven effective as adsorbents for removing heavy metals from water/wastewater, the performance and the underlying mechanism of Cd immobilization in sediments by Mn oxides remain unclear. Here, three crystallographic Mn oxides δ-MnO₂, γ-MnOOH, and Mn₃O₄ were used as amendments to investigate their potential for the in situ immobilization of Cd in lake sediment. Experimental data showed that when the sediment samples were treated with synthesized Mn oxides at dosages of 2% and 6% (w/w) for 56 days, the TCLP (toxicity characteristic leaching procedure) leachable Cd in the sediment decreased by 43.9-66.81%, and the PBET (physiologically based extraction test) extractable Cd decreased by 45.16-99.40%. Additionally, the acid-soluble fraction of Cd was partially transformed to a residual fraction, resulting in a 27.55-35.49% decrease in acid-soluble Cd and a 25.16-30.36% increase in the residual Cd fraction. Sediment pH and oxidation-reduction potential were important factors affecting the bioavailability of Cd in the remediation process. Furthermore, scanning electron microscopy, X-ray diffractometer, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy analysis illustrated that the interaction between the amendment and Cd mainly involved complexation with O-containing groups, ion-exchange as > OCd⁺, and precipitation with carbonate. The efficient remediation capacity and associated mechanism for Mn oxides provide insights for the improved restoration of heavy metal-contaminated sediment.

Release of sediment metals bound by glomalin related soil protein in waterfowls inhabiting mangrove patches

Glomalin-related soil protein (GRSP) has received extensive attention due to its ability to immobilize metals in the environment. However, whether it can enter the food chain through digestion is still unclear. Mangroves occupy the transition zone between the sea and land, have important ecological functions. Mangroves suffer from fragmentation due to human activities and urbanization. A variety of waterfowls inhabit near the mangroves and ingest sediment settled on their food inadvertently or for grit; therefore, they are ideal for revealing GRSP's role in metal enrichment. In this study, we investigated the release of metals from mangrove surface sediments and GRSP through a physiologically based extraction test. The investigated metals (As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in sediments and those bound to GRSP would be mainly released in the gizzard phase. GRSP appeared to be an efficient carrier of Cu, Zn, Pb, and As from sediments to the waterfowls via direct sediment ingestion. For instance, 3.21% and 3.34% of sediment Cu were released in the gizzard and intestinal phases, respectively, meanwhile GRSP-bound Cu contributed 5.04% and 5.42% to this flux. The continuum of GRSP enrichment - complexation of GRSP and metals - biological accessibility of GRSP-bound metals, influenced by both direct and indirect effects from major nutrients (e.g., C, N, P, and S) and metal contents (e.g., Cu, Cd, Ni), controlled the release of GRSP-bound metals during simulated digestion. Overall, this study provides new insights into the potential risk of GRSP acting as a metal delivery vehicle in the food chain.

Assessing heavy metals in surface sediments of the Seomjin River Basin, South Korea, by statistical and geochemical analysis

We investigated particle size distribution and heavy metal concentrations in surface sediments of streams and lakes in the Seomjin River Basin by comparison with Sediment Quality Guidelines (SQGs). Origins were identified using statistical and geochemical approaches. Sand was prevalent in mean particle size of surface sediments (except lakes). Mean concentrations of Pb, Zn, Cd, and Hg were similar for the Seomjin and Boseong rivers, while those of Cu, As, Cr, and Ni were approximately 1.5-2.0 times higher in the Boseong. SQGs revealed no serious pollution in the basin's site concentrations, although As and Ni levels in the Boseong had some potential for benthos toxicity. Correlation and principal component/factor analysis showed that concentrations of Cu, As, Cr, and Ni were dominant from geological origins rather than anthropogenic. The reducible fraction bound to Fe and Mn-oxides was prevalent in Pb, while the water- and acid-soluble fractions were easily exchangeable or bound to high Cd carbonates. The fraction bound to the highest lattice in residual prevailed in Zn, Cu, Cr, and Ni, accounting for 64%, 65%, 87%, and 86%, respectively. Similarly, results indicated geological origins. Risk assessment to benthos based on labile fractions (F1 + F2 + F3) were Cd (72%) < Pb (66%) < Zn (36%) ≈ Cu (35%) < Ni (14%) ≈ Cr (13%). While Cd and Pb showed the highest risk, their concentrations were relatively lower. However, Cr and Ni showed the highest concentrations but low risk levels, suggesting their pollution is unlikely to have adverse effects on benthos.

Geochemical fractionation, bioavailability, and potential risk of heavy metals in sediments of the largest influent river into Chaohu Lake, China

As the largest tributary flowing into Chaohu Lake, China, the Hangbu-Fengle River (HFR) has an important impact on the aquatic environment security of the lake. However, existing information on the potential risks of heavy metals (HMs) in HFR sediments was insufficient due to the lack of bioavailability data on HMs. Hence, geochemical fractionation, bioavailability, and potential risk of five HMs (Cr, Cu, Zn, Cd, and Pb) in HFR sediments were investigated by the combined use of the diffusive gradient in thin-films (DGT), sequential extraction (BCR), as well as the physiologically based extraction test (PBET). The average contents of Cd and Zn in the HFR Basin were more than the background values in the sediments of Chaohu Lake. A large percentage of BCR-extracted exchangeable fraction was found in Cd (8.69%), Zn (8.12%), and Cu (8.05%), suggesting higher bioavailability. The PBET-extracted fractions of five HMs were all almost closely positively correlated with their BCR-extracted forms. The pH was an important factor affecting the bioavailability of HMs. The average DGT-measured contents of Zn, Cd, Cr, Cu, and Pb were 28.07, 7.7, 3.69, 2.26, 0.5 μg/L, respectively. Only DGT-measured Cd significantly negatively correlated with Eh, indicating that Cd also had a high release risk under reducing conditions, similar to the risk assessment results. Our results could provide a reference for evaluating the potential bioavailabilities and ecological hazards of HMs in similar study areas.

Study of the micromorphology and health risks of arsenic in copper smelting slag tailings for safe resource utilization

Slag tailings are produced by "cooling-grinding-ball milling-flotation" and other processes of slag, while slag is produced by the flash smelting of the original ore. The utilization and environmental hazards of arsenic in slag tailings have become a focus of attention. This study on slag tailings reveals the presence of arsenic in copper smelting tailings from the mineralogy and leaching perspectives, and the noncarcinogenic and carcinogenic risks of arsenic to the human body were assessed by using the USEPA health risk model. The surface particles of the slag tailings were unevenly dispersed, and the mineral crystals were relatively complete. A small amount of secondary minerals had grown on the mineral surface. Most of the fine particles adhered to the surface of the main mineral to form inclusions. The mineral composition of the slag tailings was dominated by maghemite (Fe₃O₄) and fayalite (Fe₂SiO₄), and the arsenic-bearing minerals were unevenly distributed, where As (Ⅴ) fine particles were embedded in maghemite, amorphous phase and fayalite. There was a large amount of residual arsenic in the slag tailing particles, and the leaching content of arsenic in the toxicity leaching procedure was always lower than the limit of 5 mg/L. The health risk to the exposed population was evaluated by the USEPA health risk model. Since the exposed population in the industrial land is mainly adults, it is determined that the tailings will not cause harm to children's health. In this evaluation, the exposure duration (length of service of the workers) of 30 years, exposure frequency of 314 d/y and body weight of 60 kg (average weight of the workers) were taken as the parameters of three exposure pathways: hand-oral ingestion, respiratory system inhalation and skin contact. Therefore, longer activity time of the workers in the tailing workshop corresponds to a higher HI (hazard index). Although the arsenic in the slag tailings had a certain degree of bioavailability, it was not sufficient to adversely affect human health.

Respiratory bioaccessibility and solid phase partitioning of potentially harmful elements in urban environmental matrices

Studies regarding the role of geochemical processes in urban environmental matrices (UEM) and their influence on respiratory bioaccessibility in humans are scarce in humid tropical regions, especially in Brazil. Contaminated UEM are potentially hazardous to humans if particles <10 μm in diameter are inhaled and reach the tracheobronchial region. In this study, we evaluated samples collected in Brazilian UEMs with a large environmental liability left by former mining industries and in a city with strong industrial expansion. UEM samples were classified into soil, sediment and mine tailings according to the characteristics of the collection sites. The respiratory bioaccessibility of potentially harmful elements (PHE) was evaluated using artificial lysosomal fluid (ALF, pH 4.5), and the BCR-sequential extraction was performed to evaluate how the respiratory bioaccessibility of the PHE was related to the solid phase partitioning. The bioaccessible fraction (BAF) ranged from 54 to 98% for Cd; 21-89% for Cu; 46-140% for Pb, 35-88% for Mn and; 41-84% for Zn. The average BAF of the elements decreased in the following order: Soil: Cd > Pb > Mn > Zn > Cu; Tailing: Pb > Cd > Zn > Mn > Cu; and Sediments: Pb > Mn > Cd > Zn > Cu. BCR-fractions were useful to predict the PHE bioaccessibility (R² = 0.79-0.98), thus suggesting that particle geochemistry and mineralogy can influence PHE behaviour in the pulmonary fluid. Therefore, this approach provides a combination of quantitative and qualitative data, which allows us to carry out a more realistic assessment of the current situation of the potentially contaminated site and possible alternatives for decision making by the stakeholders.

Combining punctual and high frequency data for the spatiotemporal assessment of main geochemical processes and dissolved exports in an urban river catchment

The assessment of dissolved loadings and the sources of these elements in urban catchments' rivers is usually measured by punctual sampling or through high frequency sensors. Nevertheless, the combination of both methodologies has been less common even though the information they give is complementary. Major ion (Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^-, SO₄^2-, and alkalinity), organic matter (expressed as Dissolved Organic Carbon, DOC), and nutrients (NO₃^-, and PO₄^3-) are punctually measured in the Deba river urban catchment (538 km²), in the northern part of the Iberian Peninsula (draining to the Bay of Biscay). Discharge, precipitation, and Electrical Conductivity (EC) are registered with a high frequency (10 min) in three gauging stations. The combination of both methodologies has allowed the assessment of major geochemical processes and the extent of impact of anthropogenic input on major composition of riverine water, as well as its spatial and temporal evolution. Three methodologies for loading estimation have been assessed and the error committed in the temporal aggregation is quantified. Results have shown that, even though carbonates dominate the draining area, the water major ion chemistry is governed by an evaporitic spring in the upper part of the catchment, while anthropogenic input is specially noted downstream of three wastewater treatment plants, in all nutrients and organic matter. The results of the present work illustrate how the combination of two monitoring methodologies allows for a better assessment of the spatial and temporal evolution on the major water quality in an urban catchment.

Current situation and forecast of environmental risks of a typical lead-zinc sulfide tailings impoundment based on its geochemical characteristics

The potential environmental implications of a Pb (Lead)-Zn (Zinc) sulfide tailing impoundment were found to be dependent on its geochemical characteristics. One typical lead-zinc sulfide tailing impoundment was studied. Ten boreholes were set with the grid method and 36 tailings were sampled and tested. According to the results of metal content analysis, the tailing samples contained considerably high contents of heavy metals, ranging from 6.99 to 89.0 mg/kg for Cd, 75.3 to 602 mg/kg for Cu, 0.53% to 2.63% for Pb and 0.30% to 2.54% for Zn. Most of the heavy metals in the sample matrix showed a uniform concentration distribution, except Cd. Cd, Pb, Zn, and Mn were associated with each other, and were considered to be the dominant contributors based on hierarchical cluster analysis. XRD, SEM and XPS were employed for evaluation of the tailing weathering characteristics, confirming that the tailings had undergone intensive weathering. The maximum potential acidity of the tailings reached 244 kg H₂SO₄/ton; furthermore, the bioavailability of heavy metals like Pb, Cd, Cr, Cu, and Zn was 37.8%, 12.9%, 12.2%, 5.95%, and 5.46% respectively. These metals would be potentially released into drainage by the weathering process. Analysis of a gastrointestinal model showed that Pb, Cr, Ni and Cu contained in the tailings were high-risk metals. Thus, control of the heavy metals' migration and their environmental risks should be planned from the perspective of geochemistry.

Multivariate statistical analyses for water and sediment quality index development: A study of susceptibility in an urban river

In this study, multivariate statistical analyses were performed to develop water and sediment quality indexes, allowing us (i) to select with reliability the most appropriate chemical variables for the evaluation of river quality susceptibility; (ii) to weight the influence of each variable based on monitored data; (iii) to consider possible synergism or antagonism derived from the combined effect of several pollutants; and (iv) to express the quality as a deviation from selected site-specific reference conditions. For the establishment of these threshold/maximum values, combining two biological indicators related to denitrifying bacteria in sediments turned out to be applicable to ensure compliance with the European water quality standard. The joint implementation of water and sediment quality indexes assisted us in the rapid detection of the deleterious effect of different anthropogenic contamination sources, as well as the influence of hydrological regime seasonality on river quality. In addition, metal-dependent water quality appeared to be coupled to sediment dynamics, since they were preferentially adsorbed onto sediments during low flow seasons, whereas there was potential for metal mobilization to water during sediment resuspension in high flow seasons. Therefore, an annual determination of sediment quality index was also recommended as suitable tool for prospective monitoring water quality, identifying those sites which could deserve special attention during certain periods, and planning future strategies for river quality improvement. However, two limitations were found: (1) sediment was not appropriate for water physicochemical quality early monitoring due to organic matter and nutrient continuous transformation; and (2) a multimetric index did not provide a concise and definitive quality information, thus a new tool for combining with quality index was proposed for specifically evaluate the water and sediment quality by identifying pollutant/s of concern at each location.

A comprehensive analysis and source apportionment of metals in riverine sediments of a rural-urban watershed

Quantitative assessment of metal sources in sediments is essential for implementation of source control and remediation strategies. This study investigated metal contamination in sediments to assess potential ecological risks and quantify pollutant sources of metals (Cu, Zn, Pb, Cd, Cr, Co and Ni) in the Wen-Rui Tang River watershed. Total and fraction analysis indicated high pollution levels of metals. Zinc and Cd posed high ecological risk based on the risk assessment code, with the highest ecological risk found in the southwestern of the watershed. The positive matrix factorization (PMF) model was highly effective in predicting total metal concentrations and identified three contributing metal sources. An agricultural source (factor 1) contributed highly to Cu (74.1%) and Zn (42.5%), and was most prominent in the west and south-central portions of the watershed. Cd (93.5%) showed a high weighting with industrial sources (factor 2) with a hot spot in the southwest. Factor 3 was identified as a mixed natural and vehicle traffic source that showed large contribution to Cr (65.2%), Ni (63.9%) and Pb (50.7%). Spatial analysis indicated a consistent pattern between PMF-identified factors and suspected metal sources at the watershed scale demonstrating the efficacy of the PMF modeling approach for watershed analysis.

Environmental availability and oral bioaccessibility of Cd and Pb in anthroposols from dredged river sediments

Dredging and disposal of sediments onto land sites is a common practice in urban and industrial areas that can present environmental and health risks when the sediments contain metallic elements. The aim of this study was to characterise and study the environmental and toxicological availability of Cd and Pb in anthroposols from dredged river sediments. To do this, 67 surface samples spread over 12 sediment disposal sites in northern France were studied. The results showed substantial heterogeneity for this matrix in terms of physicochemical parameters and contamination degree; however, ascending hierarchical clustering made it possible to classify the samples into eight groups. For each group, the mobile fraction of Cd and Pb was studied using single EDTA extraction, solid-phase distribution was analysed with sequential extractions and toxicological availability was assessed with the oral bioaccessibility test. The results showed that (i) Cd had a higher environmental and toxicological availability than Pb; (ii) this availability depends on the physicochemical characteristics of the matrix; and (iii) it is necessary to take into account the environmental and toxicological availability of contaminants when requalifying these sites in order to propose appropriate management measures. In the first years after sediment disposal, it would appear that the environmental and toxicological availability of Cd and Pb increased (from 52.5 to 71.8% and from 28.9 to 48.9%, respectively, by using EDTA and from 50.2 to 68.5% for Cd with the bioaccessibility test). Further studies would therefore be required to confirm this trend and understand the mechanisms involved.

The importance of drying and grinding samples for determining mobile chromium fractions in polluted river sediments

A possible impact of sample preparation on the chemical fractionation results is generally underestimated in studies of forms of occurrence of heavy metals in river sediments. Our analysis of the recently published results of sequential extraction of chromium has revealed the effect of sample grinding on the result of determination of mobile chromium fractions in river sediments. This observation has been experimentally verified along with the analysation of potential effect of river sediment drying conditions on chromium distribution pattern. The studies were carried out on river sediments polluted with tannery effluents (Cr, 29.2-233 mg/kg). The determined content of chromium bound to carbonates in powdered samples was 2 to 7 times higher than those in raw river sediment samples. It was shown that the main reason was the different kinetic characteristics of chromium leaching in these sediments. Using the shrinking core model, it was found that diffusion through the "ash layer" was the rate-controlling step during the extraction of the carbonate fraction of chromium. It has been additionally confirmed that common air drying of sediment samples does not affect the results of chemical fractionation of chromium.The results of our studies are also vital for the assessment of environmental risk posed by river sediments polluted with heavy metals. In the case of sediment samples used in this study, powdering changed the risk category (RAC) from low risk to high risk. Hence, in order to achieve a realistic assessment of chromium mobility and environmental risk, it is advisable to use raw samples, despite their poorer homogeneity, and thus, lower precision of chemical fractionation results.

Evaluating the role of particle size on urban environmental geochemistry of metals in surface sediments

In this study, non-destructive techniques (X-ray Diffraction, Infrared and Scanning Electron Microscopy with Energy Dispersive spectroscopies) and invasive procedures (pseudo-total and sequential metal extraction methodologies) were used to highlight the significance of evaluating different particle sizes of sediments for assessing the potential environmental and health implications of metal geochemistry in an urban ecosystem. The variability in composition and properties between bulk (<2 mm) and fine (<63 μm) fractions influenced the availability, and by extension, the toxicity of metals. Indeed, the fine fraction presented not only higher metal pseudo-contents, but also greater available metal percentages. Besides the larger surface area per unit of mass and the high content of clay minerals, it was observed that it was principally Fe/Mn oxyhydroxides that favour adsorption of metals on the fine surface sediments. However, although we demonstrated that the origin of metals in the bulk surface sediments was predominantly lithogenic, use of the <2 mm fraction proved to be a useful tool for identifying different sources of available metals throughout the Deba River catchment. Specifically, discharges of untreated industrial and urban wastewaters, and even effluents from wastewater treatment plants were considered to greatly increase the health risk associated with metal availability. Finally, an evaluation of sediment dynamics in different hydrological conditions has highlighted the role played by each particle size as a vector of metal transport towards the coastal area. While resuspension of fine surface sediments notably induced significantly higher particulate metal concentrations in water during the dry season, resuspension of bulk surface sediments and, fundamentally, downstream transport of suspended particulate matter became more relevant and lowered the ecological risk during the wet season. Greater attention therefore needs to be paid to the new hydrological scenarios forecast to result from climate change, in which longer seasons with low river discharges are forecast.

Treated and untreated wastewater effluents alter river sediment bacterial communities involved in nitrogen and sulphur cycling

Studying the dynamics of nitrogen and sulphur cycling bacteria in river surface sediments is essential to better understand their contribution to global biogeochemical cycles. Evaporitic rocks settled at the headwater of the Deba River catchment (northern Spain) lead to high values of sulphate concentration in its waters. Besides, the discharge of effluents from untreated and treated residual (urban and industrial) wastewaters increases the concentration of metals, nutrients and organic compounds in its mid- and low-water courses. The aim of this study was to assess the impact of anthropogenic contamination from untreated and treated residual and industrial wastewaters on the structure and function of bacterial communities present in surface sediments of the Deba River catchment. The application of a quantitative functional approach (qPCR) based on denitrification genes (nir: nirS+nirK; and nosZ), together with a 16S rRNA gene metabarcoding structural analysis, revealed (i) the high relevance of the sulphur cycle at headwater surface sediments (as reflected by the abundance of members of the Syntrophobacterales order, and the Sulfuricurvum and Thiobacillus genera) and (ii) the predominance of sulphide-driven autotrophic denitrification over heterotrophic denitrification. Incomplete heterotrophic denitrification appeared to be predominant in surface sediments strongly impacted by treated and untreated effluents, as reflected by the lower values of the nosZ/nir ratio, thus favouring N₂O emissions. Understanding nitrogen and sulphur cycling pathways has profound implications for the management of river ecosystems, since this knowledge can help us determine whether a specific river is acting or not as a source of greenhouse gases (i.e., N₂O).

Environmental assessment concerning trace metals and ecological risks at Guanabara Bay, RJ, Brazil

Three-stage sequential extraction BCR was applied to surface sediments from the west part of Guanabara Bay to assess the mobility of Zn, Cu, Pb, Ni, Cr, and Mn. Results were satisfactory for the analysis of certificate standard material (BCR 701), with recoveries between 71 (Cu) and 123% (Cr). Evaluation of organic matter composition classified the area as eutrophic (CHO:PRT > 1), with aged organic detritus at some stations. Zn exhibited by far the greatest bioavailability, with 43.49% of its concentrations associated with the exchangeable fraction. Cu and Cr showed stronger affinity for organic matter, with 51.18 and 48.73% of their concentrations, respectively, bounded to the oxidizable fraction. Pb presented higher concentrations in the reducible fraction (45.41%). The strongest lithogenic contribution was shown by Ni (31.91%) and Mn (35.44%). PCA clearly showed the determinant role of organic matter and fine sediments in the distribution of metals in the study area and also a common source for these elements, with the exception of Cu. Risk Assessment Code (RAC) established Zn as the most concerning element in the study area. The decreasing mobility order, based on the sum of the three extractable fractions of BCR, was Pb > Cu > Cr > Zn > Ni > Mn. The comparison of the results with sediments quality guidelines (SQG) proved fractionation to be mandatory in the evaluation of effective ecological risk concerning trace elements in sediments.