Distribution and adsorption of metals on different particle size fractions of sediments in a hydrodynamically disturbed canal

Elevated lead mobility in sediments of a eutrophic drinking water reservoir during spring and summer seasons: Insights from isotopic signatures

Lead (Pb) pollution in sediments remains a major concern for ecosystem quality due to the robust interaction at the sediment/water interface, particularly in shallow lakes. However, understanding the mechanism behind seasonal fluctuations in Pb mobility in these sediments is lacking. Here, the seasonal variability of Pb concentration and isotopic ratio were investigated in the uppermost sediments of a shallow eutrophic drinking lake located in southeast China. Results reveal a sharp increase in labile Pb concentration during autumn-winter period, reaching ∼ 3-fold higher levels than during the spring-summer seasons. Despite these fluctuations, there was a notable overlap in the Pb isotopic signatures within the labile fraction across four seasons, suggesting that anthropogenic sources are not responsible for the elevated labile Pb concentration in autumn-winter seasons. Instead, the abnormally elevated labile Pb concentration during autumn-winter was probably related to reduction dissolution of Fe/Mn oxides, while declined labile Pb concentration during spring-summer may be attributed to adsorption/precipitation of Fe/Mn oxides. These large seasonal changes imply the importance of considering seasonal effects when conducting sediment sampling. We further propose a solution that using Pb isotopic signatures within the labile fraction instead of the bulk sediment can better reflect the information of anthropogenic Pb sources.

Adsorption and distribution of heavy metals in aquatic environments: The role of colloids and effects of environmental factors

The study investigated the distributions of heavy metals (Cd, Cr, Cu, Mn, and Pb) between dissolved fraction (<0.7 µm) and particles (>0.7 µm) during the adsorption process. The dissolved fraction was further separated into truly dissolved (<3 kDa) and colloidal (3 kDa-0.7 µm) fractions. Significant metal adsorption occurred on the colloids, resulting in their aggregation into particles, which in turn influenced the particle adsorption kinetics. Colloids could either accelerate or inhibit the transformation of metal ions into particulates, depending on their stability. Competitive metals for colloids (Pb and Cr) were more susceptible to the effects of colloids than other elements. DOM was the predominant environmental factor influencing colloid behavior. The XDLVO theory showed that DOM enhanced the negative charge of colloids and made the colloid surface more hydrophilic, inhibiting the aggregation of colloids. DOM resulted in substantial increases in the concentrations of colloidal Pb and Cr from 0.31 μg/L and 4.58 μg/L to 20.52 μg/L and 43.51 μg/L, respectively, whereas the increment for less competitive metals (Cd and Mn) was smaller. These findings suggest that the distribution of heavy metals is influenced not only by adsorption from particles and ions but also by the complex dynamics of colloids.

Examining temporal trends in heavy metal levels to analyze sediment pollution dynamics in the Saida urban watershed (N-W Algeria)

The study focuses on current pollution in the Saïda basin, a semi-arid region in north-western Algeria. By analyzing sediments, the study provides interesting results on urban pollution and its environmental impact. The research consists of two main phases, each addressing different aspects of pollution. In the first phase, different pollution indicators are used to analyze heavy metals and organic pollutants in urban drainage sediments. The results are compared with sediment quality guidelines, regulatory thresholds, and local and international references. Most of the metallic contaminants exceed the toxicity levels established by the continental crust and sediment quality guidelines, suggesting an anthropogenic origin. In addition, contamination indices show significant accumulation. In this context, the results highlight the importance of accumulation and transport processes in urban sediments. Hydrological parameters significantly influence heavy metal distribution mechanisms. Remarkable variations between copper (Cu) and lead (Pb) suggest a combined or singular source during transport. Conversely, chromium (Cr), nickel (Ni), and iron (Fe) are mainly derived from natural lithological sources. Cadmium (Cd) is associated with anthropogenic sources related to the agricultural use of phosphate fertilizers, whereas zinc (Zn) is mainly derived from physical corrosion processes. In the second phase, a combined descriptive and multivariate statistical analysis examines the mobility and distribution of heavy metals and their relationships with organic matter (OM) over time. Pronounced temporal variations in Cd, Zn, and Cu concentrations are attributed to human activities. Strong correlations exist between OM and cobalt (Co), Cu and Pb, confirming the ability of OM to adsorb these metals under specific geochemical conditions associated with waste disposal. Conversely, Zn, Cd, Cr, and Ni show weak or negative correlations with OM, suggesting diverse sources, including potential agricultural, industrial, and natural origins. The dendrogram confirms the existence of previously identified contaminant groups, suggesting common sources and potential co-occurrence patterns. This analysis highlights the role of the drainage network as a physico-chemical reactor in the mobilization of contaminants. It underlines the importance of sediment interactions in urban pollution processes. Finally, recommendations are proposed to ensure effective pollution control and remediation. PRACTITIONER POINTS: Useful information on pollution and its environmental impact is provided by the analysis of sediments in the urban basin of Saida (NW-Algeria). The results of this study indicate high levels of heavy metals in the sediments, in excess of toxicity limits, and evidence of anthropogenic sources. Temporal variations in metal concentrations indicate the influence of human activities. The study has made it possible to identify the sources, to understand the mobility and distribution, and to control the contamination by heavy metals in the urban sediments. Drainage system serves as a pathway for dispersing contaminants.

One-step processing of waste dredged slurry into planting soil by targeted pretreatment and vacuum filtration

A novel method, targeted pretreatment and vacuum filtration (TP-VF), is introduced and validated in this study. TP-VF offers a one-step solution for efficiently dewatering dredged slurry (DS) characterized by heavy metal contamination, high salinity, and excessive moisture content. This innovative approach combines targeted pretreatment (TP) and vacuum filtration (VF) to transform DS into the viable planting soil. TP encompasses a dual optimization strategy that enhances both slurry dewatering efficiency and the quality of the resultant planting soil (cake). By employing flocculation pretreatment, TP increases the size of flocs and enlarges cake pores, leading to improvements in dewatering efficiency and infiltration rates. Additionally, targeted pretreatment results in the discharge of approximately 90% of heavy metal ions and most salts with the filtrate. Remarkably, the addition of chelating agents and freshwater as part of the pretreatment process positively impacts soil quality without compromising floc size or dewatering efficiency. Comparatively, TP-VF demonstrates a substantial reduction of 35.81% in operational costs when contrasted with the traditional two-step process, concurrently diminishing the potential for secondary environmental pollution. This study highlights TP-VF as a promising advancement in sustainable slurry management, addressing pressing environmental challenges while optimizing resource utilization.

Geochemical controls on the distribution and bioavailability of heavy metals in sediments from Yangtze River to the East China Sea: Assessed by sequential extraction versus diffusive gradients in thin-films (DGT) technique

This study conducted a comprehensive investigation on the distribution and bioavailability of heavy metals (Cr, Co, Ni, Cu, Zn, Cd and Pb) in sediments along two typical transects from Yangtze River to the East China Sea continental shelf that spanning large physicochemical gradients. Heavy metals were mainly associated with the fine-grained sediments (enriched with organic matter), exhibiting decreasing trends from nearshore to offshore sites. The turbidity maximum zone showed the highest metal concentrations, which evaluated as polluted for some tested metals (especially Cd) using the geo-accumulation index. Based on the modified BCR procedure, the non-residual fractions of Cu, Zn and Pb were higher within the turbidity maximum zone, and significantly negatively correlated with bottom water salinity. The DGT-labile metals all positively correlated with the acid-soluble metal fraction (especially for Cd, Zn and Cr), and negatively correlated with salinity (except Co). Therefore, our results suggest salinity as the key factor controlling metal bioavailability, which could further modulate metal diffusive fluxes at the sediment-water interface. Considering that DGT probes could readily capture the bioavailable metal fractions, and reflect the impacts of salinity, we suggest DGT technique can be used as a robust predictor for metal bioavailability and mobility in estuary sediments.

Effect of organic acids and soil particle size on heavy metal removal from bulk soil with washing

To evaluate the effect of soil particle size on heavy metals removal by washing, two soil samples were collected around a lead-zinc mining area (SM) and lead-zinc smelter (SS). The total content of Cd, Pb and Zn in SM and SS were determined. And the effect of soil particle size on Cd removal by low molecular organic acids was studied. The results showed that Cd was the main pollutant and the total content of Cd in SS can reach to 24.8 mg Kg^-1. 68.4% of the total Cd in SM existed in the form of residual state, while 54.7% of the total Cd in SS was in weak acid extractable state. About 50.0% of the Cd distributed in < 2 μm soil size fraction. The washing results indicated that citric acid was a highly efficient eluent among the five low molecular weight organic acids (citric acid, malic acid, tartaric acid, oxalic acid and acetic acid). After washing, 40% and 69.6% of the total Cd in SS and SM can be removed by citric acid, respectively. While only 18.7-40.2% and 32.6-68.7% of Cd was removed from different size fractions of SM and SS, respectively. The species of Cd in soil size fractions affected the removal effect of citric acid. The citric acid can easily remove the weak acid extractable and reducible form of Cd in soil. After eluted by citric acid, the bioavailability of Cd in soil decreased markedly, and the highest decreasing rate reached 93%.

Geochemical speciation, ecological risk, and source identification of heavy metal(loid)s in sediments and waters from Musa Estuary, Persian Gulf

Surface sediment and water samples from 12 stations were collected from Musa Estuary. Metals concentrations (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sb, and Zn) were analyzed by ICP-MS. The highest contribution to ecological risk belonged to Cd (49 %) based on the PERI index. The Tessier procedure showed that with increasing contamination, exchangeable and carbonate fractions of Cd, Pb, Ni, Zn, and Cu increased by 25 %, 18 %, 17 %, 10 %, and 9 %, respectively. Cadmium and Pb have a high risk of release according to mobility factor (30 < MF < 50) and individual contamination factor (3 < ICF < 6) indices. Cluster analysis revealed that Al-Fe-Co-V-Mn-Cu-Pb derived from lithogenic resources, while As-Cd-Ni-Zn-Cr originated from anthropogenic sources. The adsorption of Co, Ni, V, and Zn to sediments was strongly influenced by Eh/pH, DOC/temperature, and salinity (r > 0.79, r < -0.78, and r < -0.69; p < 0.01).

Pollution characteristics and source identification of farmland soils in Pb-Zn mining areas through an integrated approach

Long-term mining activities have caused serious heavy metals contamination of farmland soils. In this study, we investigated the concentrations, distributions, accumulations, potential ecological risk, and sources of eight heavy metals in farmland soils of Pb-Zn mining areas. According to the soil standard GB15618-2018, Cd was the most contaminated, followed by Pb and Zn. The geo-accumulation index showed that Pb, Zn, Cd, and Hg accumulated seriously. The potential risk index indicated that Cd, Hg, and Pb were the main environmental risk elements. An integrated approach combining multivariate statistical analysis, PMF, and GIS mapping was used to analyze the sources of heavy metals. Four main sources were identified and quantified: (1) mining activities source, the main source of Cd (71.09%) and Zn (61.88%); (2) agricultural activities source, dominated by Hg (73.01%); (3) atmospheric deposition sources, with Pb (85.11%) as the main contributor; (4) natural source, characterized by Cr (72.96%), Ni (66.04%), As (55.98%) and Cu (37.70%). This study would help us understand the pollution characteristics and sources of farmland soils in mining areas and provide basic information for the next step of pollution control and remediation.

Toxicity risks associated with trace metals call for conservation of threatened fish species in heavily sediment-laden Yellow River

Trace metals and metalloids in aquatic ecosystems may lead to adverse effects on the survival of fish, especially in the sensitive life stages of vulnerable species. It is still unknown whether threatened fish species in the heavily sediment-laden Yellow River are exposed to toxicity risks associated with multiple trace metals. Herein, we analyzed the concentrations of trace metals in aquatic environmental media and fish tissues across the Yellow River mainstream and assessed the level of metal toxicity to threatened fish. Significantly different concentrations of trace metals in fish tissues were measured between at least two categories among near-threatened, vulnerable, endangered, and critically endangered fish. No metal showed a higher concentration in demersal fish than in pelagic fish. Substantially low metal toxicity was observed for the gill of Rhinogobio nasutus (near-threatened) in the upper reaches, as well as for the gill and liver of Silurus lanzhouensis (endangered) in the middle reaches. High contents of suspended sediment in water and high metal concentrations in sediment and suspended matter could influence the survival and reproduction of fish, especially those already with threatened status.

The relationships between fractal parameters of soil particle size and heavy-metal content on alluvial-proluvial fan

The particle size distribution (PSD) of soil is an important factor in determining heavy-metal content, mobility, and transformation. One method of describing the soil PSD is applying fractal theory. This study explored the use of fractal theory to characterize soil PSD in the alluvial-proluvial fan located downstream of the Yangshuo lead‑zinc mine. The relationships between fractal parameters of soil PSD and heavy-metal content were analyzed. The results showed that soil in front of the mountain (FM) had higher clay content than soil on the mountain slope (MS) or in the middle of the alluvial-proluvial fan (MF). Among the different sections of the alluvial-proluvial fan, MS had the largest capacity dimension D(0), information dimension D(1), correlation dimension D(2), single fractal dimension D, spectral width Δα, and D(1)/D(0), whereas MF had the greatest symmetry degree Δf. Soil of MS had the highest ω (Cr) and ω (Fe), while FM had the highest ω (Zn), ω (Mn), ω (Pb), ω (Cu), ω (As), ω (Sb), and ω (Cd). Fractal parameters of soil PSD and soil mechanical composition were significantly correlated, while both variables were correlated with heavy-metal content. Fractal parameters can be used to indicate heavy-metal content when heavy metals migrate due to migration of particle size. This study thus introduces an empirical method for evaluating heavy-metal content in soil and analyzing the mechanisms of their migration, making a strong contribution to developing strategies that limit heavy-metal pollution.

Bioaccumulation and health risks of multiple trace metals in fish species from the heavily sediment-laden Yellow River

The health risk caused by metal pollution is a global concern due to potential metal bioaccumulation, toxicity, and carcinogenicity with multiple sources and pathways. Here, the factors influencing metal bioaccumulation in more than a thousand fish individuals were investigated along a 5464 km continuum of the heavily sediment-laden Yellow River and the health risks to humans were evaluated. The average concentrations of Cr, Zn, As, Cu, Cd, and Pb were below the permissible limits established by domestic and foreign organizations. The fish showed biomagnification of Se and Sn through trophic transfer and a growth dilution effect for V, Mn, Co, Ni, Cu, Zn, As, Cd, and Ba. The concentrations and distributions of most metals in fish were mainly influenced by the trophic levels (δ¹⁵N) of fish and the content of the metals in the aquatic environment. The consumption of fish from the Yellow River does not pose a noncarcinogenic risk to the health of adults and juveniles. Cr and As could cause carcinogenic risks, and Cd and Pb also have carcinogenic risks, but these were within an acceptable range. The carcinogenic risks of fish consumption were relatively low in regions with low levels of metal pollution, such as the source region, while the risks were high in regions with heavy pollution and carnivorous fish at high trophic levels. In response to this threat, people can minimize these risks by adjusting their diet and appropriately reducing their consumption of aquatic products from the Yellow River.

Mobilization of colloids during sediment resuspension and its effect on the release of heavy metals and dissolved organic matter

Natural colloids are important in mobilizing pollutants in aquatic environments. This study investigated the mobilization and aggregation of natural colloids during the sediment resuspension and re-sedimentation processes using nanoparticle tracking analysis. The metals and organic matter in overlying water were divided and examined in dissolved (<0.45 μm), colloidal (3 kDa - 0.45 μm), and truly dissolved (<3 kDa) forms. Excitation emission matrix-parallel factor analysis (EEM-PARAFAC) was used to characterize the dissolved organic matter (DOM). In overlying water, most natural colloids were < 200 nm before resuspension. An evident mobilization of colloids and an increase in colloid size were observed during resuspension. The formation of particles (>0.45 μm) and decreases of small colloids (<200 nm) indicated that resuspension promoted the aggregation of colloids. Mobilization of colloids was accompanied by increases in concentrations of Fe, Al, and organic carbon in colloidal fractions, which could be related to the formation of mineral-organic complexes under an oxic environment. The release of DOM from sediments mainly contributed to the truly dissolved humic-like fraction, and colloidal organic carbon accounted for, on average, 20 % of the total dissolved organic carbon (DOC). Fe and Al had the highest colloidal proportions as they are major compositions of inorganic colloids. Substantial removal of dissolved Al, Fe, Pb, and Zn occurred when colloids aggregated in the overlying water. Although the adsorption of suspended particles may also decrease the concentrations of dissolved metals, the increased proportions of colloidal metals indicated a possible role of colloids in this process. These findings provide insight into the behavior of colloids during the resuspension process and indicate that the aggregation of colloids could promote the removal of dissolved matter.

Water quality degradation drives the release and fractionation transformation of trace metals in sediment

The behavior and stability of trace metals in sediment are important to the ecology of rivers. Deteriorated water quality from domestic wastewater discharge has been studied extensively, but the effect of domestic wastewater on trace metals in sediment is poorly understood. To investigate this, we simulated the water quality degradation process through leaching experiments using domestic wastewater as the leaching solution. The results indicated that domestic wastewater does not negatively influence the stability and fractionation of trace metals in this experimental model, the existence of phosphate was the pacing factor for this phenomenon. Single-factor control treatment groups showed that a leaching solution with pH < 6, NaCl, NH₄Cl, NaNO₃, and humic acid promoted the dissolution of trace metals from sediment, whereas NaH₂PO₄ inhibited this process and increased their stability in sediment. The response of trace metals behavior to NaCl, NH₄Cl, and extreme pH levels was more sensitive than NaNO₃ and HA. Chloride ions can form relatively stable compounds with trace metals, reducing the activity of trace metals in the solution and promoting the release of trace metals from sediment, but it has positive effect on Pb and Zn stability and negative effect on Cu. Extreme pH conditions (pH > 10) and higher concentrations of leaching solutions (NaCl, NH₄Cl, NaNO₃, and HA) led to an increase in the Cu leaching concentration from sediment and the transformation to unstable fractions, while the impact on the stability of Zn and Pb was beneficial or had little effect. These experiment groups indicated that phosphate is beneficial to the stability of trace metals even at the condition of water degradation and can decrease the ecological risk caused by trace metals.

Distribution and variation of metals in urban river sediments in response to microplastics presence, catchment characteristics and sediment properties

Despite well documented studies on metal pollutants in aquatic ecosystems, knowledge on the combined effects of catchment characteristics, sediment properties, and emerging pollutants, such as microplastics (MPs) on the presence of metals in urban river sediments is still limited. In this study, the synergistic influence of MPs type and hazard indices, catchment characteristics and sediment properties on the variability of metals present in sediments was investigated based on a typical urban river, Brisbane River, Australia. It was noted that the mean concentrations of metals in Brisbane River decreases in the order of Al (94,142 ± 12,194 μg/g) > Fe (62,970 ± 8104 μg/g) > Mn (746 ± 258 μg/g) > Zn (196 ± 29 μg/g) > Cu (50 ± 19 μg/g) > Pb (47 ± 25 μg/g) > Ni (25 ± 3 μg/g) while the variability of metals decreases in the order of Pb > Cu > Mn > Al > Ni > Zn > Fe along the river. According to enrichment factor (Ef) contamination categories, Mn, Cu and Zn exert a moderate level of contamination (Ef > 2), while Fe, Ni, and Zn show slight sediment pollution (1 <Ef < 2). In the case of Pb, extremely high enrichment (Ef > 3) was found at sampling locations having a high urbanisation level and traffic related activities. Crustal metal elements (namely, Al, Fe, Mn) were found to be statistically significantly correlated with sediment properties (P < 0.05). Anthropogenic source metals (namely, Cu, Ni, Pb, Zn) were observed to be highly correlated with catchment characteristics. Additionally, the presence of metals in sediments were positively correlated with MPs concentration, and negatively correlated with MPs hazard indices. The outcomes of this study provide new insights for understanding the relationships among metals and various influential factors in the context of urban river sediment pollution, which will benefit the formulation of risk assessment and regulatory measures for protecting urban waterways.

Evaluation of toxic metals in different grain size fractions of sediments of the southeastern Black Sea

Surficial marine sediment samples were collected along the southeastern Black Sea (Trabzon) coast. The sampling was conducted in June 2019 from eleven stations, with the depths varying between 8 and 30 m. Metal concentrations (Cu, Pb, Zn, Ni, As, and Cr) were evaluated in four different sediment size fractions; 0.063 mm (F1), 0.125 mm (F2), 0.25 mm (F3), and 0.5 mm (F4). Geoaccumulation Index (I_GEO), Sediment Enrichment Factor (SEF), Ecological Risk (Er), and Potential Ecological Risk Index (RI) were used to determine potential anthropogenic hotspots. Temperature, pH, salinity, dissolved oxygen, and total organic carbon were determined to assess the variation across the sampling area. The highest metal concentrations (Cu:113.4 ± 45.1; Pb:85.9 ± 28.9; Zn: 138.6 ± 18.8; Ni:37.8 ± 7.6; As:14.1 ± 3.6; and Cr: 29.9 ± 5.4 ppm) were obtained in the smallest sediment fraction 0.063 mm (F1). The fractions of sediment structure were polluted by Cu, Pb, and As from moderate and severe levels according to I_GEO and SEF.

Effect of dissolved organic matter and heavy metals ions on sorption of phenanthrene at sedimentary particle scale

Human activities significantly increase the input of offshore heavy metals and organic pollutants. Although particle-scale and heterogeneous organic matters are fundamentally important to the fate of hydrophobic organic compounds (HOCs), deep understanding of the adsorption mechanism of HOCs on soil/sediment particles under the influence of heavy metal and organic pollution input is needed. This study investigates the effects of exotic DOM and heavy metals ions on the phenanthrene adsorption on sediment fractions. The adsorption experiments demonstrated that exotic DOM increased phenanthrene adsorption amount of sediment, with the greatest enhancement on clay particles (<2 µm). Nevertheless, the mechanism was differentiated accordingly to particle dimensions in terms of increased binding coefficients and mobility of phenanthrene. Furthermore, the introduction of heavy metals considerably enhanced the nonlinear sorption of phenanthrene. The Freundlich exponent N reduced by 0.01-0.24 when adding Cu²⁺, Zn²⁺ and Pb²⁺, especially for coarse particles (31-63 µm) fraction. In comparison, the enhancement of nonlinearity adsorption by Cu²⁺ and Zn²⁺ is significantly lower than Pb²⁺ ions. To our knowledge, the particle-scale study broadens the horizon of environmental fate and ecological risk of HOCs in intertidal regions, which is significantly affected by tidal action.

Trace element concentrations in forage seagrass species of Chelonia mydas along the Great Barrier Reef

Toxic metal exposure is a threat to green sea turtles (Chelonia mydas) inhabiting and foraging in coastal seagrass meadows and are of particular concern in local bays of the Great Barrier Reef (GBR), as numerous sources of metal contaminants are located within the region. Seagrass species tend to bioaccumulate metals at concentrations greater than that detected in the surrounding environment. Little is known regarding ecotoxicological impacts of environmental metal loads on seagrass or Chelonia mydas (C. mydas), and thus this study aimed to investigate and describe seagrass metal loads in three central GBR coastal sites and one offshore site located in the northern GBR. Primary seagrass forage of C. mydas was identified, and samples collected from foraging sites before and after the 2018/2019 wet season, and multivariate differences in metal profiles investigated between sites and sampling events. Most metals investigated were higher at one or more coastal sites, relative to data obtained from the offshore site, and cadmium (Cd), cobalt (Co), iron (Fe) and manganese (Mn) were found to be higher at all coastal sites. Principle Component Analysis (PCA) found that metal profiles in the coastal sites were similar, but all were distinctly different from that of the offshore data. Coastal foraging sites are influenced by land-based contaminants that can enter the coastal zone via river discharge during periods of heavy rainfall, and impact sites closest to sources. Bioavailability of metal elements are determined by complex interactions and processes that are largely unknown, but association between elevated metal loads and turtle disease warrants further investigation to better understand the impact of environmental contaminants on ecologically important seagrass and associated macrograzers.

Synthesis and Characterization of Mesoporous Aluminum Silicate and Its Adsorption for Pb (II) Ions and Methylene Blue in Aqueous Solution

Aluminum silicate powder was prepared using two different syntheses: (1) co-precipitation and (2) two-step sol-gel method. All synthesized powders were characterized by various techniques including XRD, FE-SEM, FT-IR, BET, porosimeter, and zetasizer. The particle morphology of the synthesized aluminum silicate powder was greatly different depending on the synthesis. The synthesized aluminum silicate powder by co-precipitation had a low specific surface area (158 m²/g) and the particle appeared to have a sharp edge, as though in a glassy state. On the other hand, synthesized aluminum silicate powder by the two-step sol-gel method had a mesoporous structure and a large specific surface area (430 m²/g). The aluminum silicate powders as adsorbents were characterized for their adsorption behavior towards Pb (II) ions and methylene blue in an aqueous solution performed in a batch adsorption experiment. The maximum adsorption capacities of Pb (II) ions and methylene blue onto the two-step sol-gel method powder were over four-times and seven-times higher than that of the co-precipitation powder, respectively. These results show that the aluminum silicate powder synthesized with a two-step sol-gel method using ammonia can be a potential adsorbent for removing heavy metal ions and organic dyes from an aqueous solution.

Expanding the Sediment Transport Tracking Possibilities in a River Basin through the Development of a Digital Platform—DNS/SWAT

Simulation of stochastic and variable sediment transport processes within models still poses a big challenge, especially in mountainous areas. Since sediment transport, including erosion and deposition, remains an unceasing problem in many areas, sediment modeling is perceived as a possible solution. This article combines a review of the selected sediment models with a presentation of the effects of several years of research using the DNS digital platform in the Western Carpathians. The review focuses on the main advantages and gaps in selected modeling tools with particular emphasis on one of the most popular: SWAT. The description of the digital platform—DNS is an example of how to answer these gaps by combining subsequent models, methods, and databases using their best features. To accentuate the benefits of such an approach, the effects of combining subsequent models (AdH/PTM) and methods (fingerprinting) on a common digital DNS space are presented, on the example of the Raba River (basin). In this way, both unique possibilities of estimating the amount of contamination carried with sediment particles and their sources, as well as sequencing of sedimentation in the reservoir, taking into account its subsequent zones, were obtained.

The Relationship between Particle Size and Element Distribution in Stream Sediments from the Dongyuan W-Mo Deposit, Eastern China

Particle size exerts significant control on the concentration of elements in stream sediments and is therefore critical in stream sediment-based geochemical exploration, which has proved important in China’s National Geochemical Mapping Project. There are various geographical landscapes in China with different distribution characteristics of stream sediments. Therefore, we studied the relationship between particle size and element distribution in stream sediments, which is always a crucial but challenging issue in geochemical surveys. The distributions of minerals and elements in eight size fractions of stream sediments (2–0.84, 0.84–0.42, 0.42–0.25, 0.25–0.177, 0.177–0.125, 0.125–0.096, 0.096–0.074, and <0.074 mm) from the Dongyuan W-Mo deposit in eastern China were studied. The results show that the 2–0.25 mm particle size fraction of stream sediments is composed mainly of rock debris and various minerals from broken bedrock upstream, while the <0.25 mm fraction is composed mainly of clay, individual minerals, and organic matter. The pilot survey results prove that using 2–0.25 mm as the sampling particle size fraction is better than using <0.25 mm, especially in geochemical prospecting and geological body delineation. Sampling the 2–0.25 mm particle size fraction of stream sediments can help to delineate proven ore bodies, ore-related anomalies, and geological bodies more effectively and more credibly. The suggested sampling particle size fraction for a stream sediment geochemical survey in a humid to semi-humid low mountain landscape in eastern China is therefore 2–0.25 mm, rather than the particle size fraction of <0.25 mm that was used for sampling in this area before. This paper depicts a successful example for determining the optimal sampling particle size fraction for stream sediment-based geochemical exploration.

Mn(II) Sorption on Stream Sediments Sampled in Manganese Mining Area: Dynamics and Mechanisms

The stream sediments that have been impacted by manganese (Mn) containing wastewater for decades contain not only abundant microorganisms but also organic/inorganic substances. To achieve effective treatment of manganese (Mn)-containing effluent and recovery of Mn from water/sediments, the Mn(II) sorption behaviors and mechanism on sediments of a stream in Mn mining areas were studied. In addition, the study analyzed the effects of various factors (initial concentration, solution pH, sediment dose, contact time, and coexisting cations) on the Mn sorption efficiency of Daxin sediments, and explored the contribution of microbial activity in the sediment sorption of Mn(II). The results showed that the sorption process of Mn(II) on the sediments was consistent with the Elovich and Freundlich models, and the removal of heavy metals was maximum at 40 °C (62.47–98.93%), pH = 8 (77.51%), initial concentration of 1 mmol·L−1 (95.37%) and sediment dosing of 12 g·L−1 (98.93%). The addition of 50 mM NaN3 inhibited the microbial activity in the Daxin sediment, reducing the sorption and removal rates of Mn(II) by 0.605 mg·g−1 and 8.92%, respectively. After sorption, the proportion of the Fe–Mn oxidation(iron–manganese) state in Daxin sediments decreased from 54% to 43%, while the proportion of the exchangeable state increased by 10.80%. Microorganisms in the sediment had a positive effect on inhibiting heavy metal migration and reducing the bioavailability of contaminants in the soil. Through this study, we hope to further understand the sorption and desorption mechanism of manganese by stream sediments in manganese ore areas, so as to provide a guide on the management and recovery of Mn from stream sediments in manganese mining areas.

Tissue-specific distribution and bioaccumulation pattern of trace metals in fish species from the heavily sediment-laden Yellow River, China

The Yellow River is one of the largest contributors to the global riverine sediment flux from the land to the ocean. Tissue-specific bioaccumulation of trace metals in fish from heavily sediment-laden rivers remains unclear to date. The concentrations and distributions of trace metals in water, suspended matters, sediments, and various fish tissues were investigated in the mainstem of the Yellow River were investigated. The concentrations of most metals in abiotic media were high in the Gan-Ning-Meng of upstream and downstream segments, and were highest in fine-sized suspended matters. The highest concentrations of most metals were in the gill and liver, followed by the gonad, and lowest in the muscle, and there were a significant overall differences among the tissues. The concentrations of metals in some tissues (e.g., muscle and gill) significantly differed among regions and feeding habits. The highest values of the bioaccumulation factor for suspended matters (BF_SPM) were observed in the midstream region (e.g., reaching to 19.0 for Se in the liver). This was determined by metal type and tissue specificity, food composition, and concentration of metals in abiotic media. The results highlight the significance of suspended matters for the distribution of trace metals in abiotic and biotic media.

Transport and partitioning of metals in river networks of a plain area with sedimentary resuspension and implications for downstream lakes

This study showed that metal transport and partitioning are primarily controlled by suspended solids with seasonal flow regimes in plain river networks with sedimentary resuspension. Eight metal species containing iron (Fe), manganese (Mn), cadmium (Cd), chrome (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn), in multiple phases of sediments, suspended solids (>0.7 μm), colloids (1 nm-0.7 μm) and dissolved phase (<1 nm) were analysed to characterize their temporal-spatial patterns, partitioning and transport on a watershed scale. Metal concentrations were associated with suspended solids in the water column and decreased from low flow to high flow. However, metal partitioning between particulate phase (suspended solids) and dissolvable phases (colloids and dissolved phase) was reversed and increased from low flow to high flow with decreased concentration of total suspended solids and median particle size. Partition coefficients (k_p) showed differences among metal species, with higher values for Pb (354.3-649.0 L/g) and Cr (54.2-223.7 L/g) and lower values for Zn (2.5-25.2 L/g) and Cd (17.3-21.0 L/g). Metal concentrations in sediments increased by factors of 1.2-3.0 from upstream to downstream in watersheds impacted by urbanization. The behaviours of metals in rivers provide deeper insight into the ecological risks they pose for downstream lakes, where increased redox potential and organic matter may increase metal mobility due to algal blooms. Areas with heavy pollution of metals and the transport routines of metals in the river networks were also revealed in our research.

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.

Adsorption-desorption behavior of heavy metals in aquatic environments: Influence of sediment, water and metal ionic properties

Limited knowledge of the combined effects of water and sediment properties and metal ionic characteristics on the solid-liquid partitioning of heavy metals constrains the effective management of urban waterways. This study investigated the synergistic influence of key water, sediment and ionic properties on the adsorption-desorption behavior of weakly-bound heavy metals. Field study results indicated that clay minerals are unlikely to adsorb heavy metals in the weakly-bound fraction of sediments (e.g., r = -0.37, kaolinite vs. Cd), whilst dissociation of metal-phosphates can increase metal solubility (e.g., r = 0.61, dissolved phosphorus vs. Zn). High salinity favors solubility of weakly-bound metals due to cation exchange (e.g., r = 0.60, conductivity vs. Cr). Dissolved organic matter does not favor metal solubility (e.g., r = -0.002, DOC vs. Pb) due to salt-induced flocculation. Laboratory study revealed that water pH and salinity dictate metal partitioning due to ionic properties of Ca²⁺ and H⁺. Selectivity for particulate phase increased in the order Cu>Pb>Ni>Zn, generally following the softness (2.89, 3.58, 2.82, 2.34, respectively) of the metal ions. Desorption followed the order Ni>Zn>Pb>Cu, which was attributed to decreased hydrolysis constant (pK1 = 9.4, 9.6, 7.8, 7.5, respectively). The study outcomes provide fundamental knowledge for understanding the mobility and potential ecotoxicological impacts of heavy metals in aquatic ecosystems.

The importance of organic carbon as a coadjutant in the transport of pollutants

Dissolved organic carbon (DOC) is a physicochemical parameter widely used in the evaluation of surface water quality; however, its role as an agent of transport and transference of pollutants sometimes is still disregarded. The heterogeneous composition of DOC, predominantly composed of humin, humic and fulvic acids, renders it an inherent capacity to bind to organic and inorganic pollutants. This is an important feature when the knowledge of present and future conditions of aquatic environments is of concern. Some authors concluded that DOC is a controlling agent of mobility of metals, phosphorus, herbicides, and pesticides, among others. Nevertheless, some physical and chemical conditions in the water column and in the sediment can immobilize the contaminants and make the DOC less soluble, which will hamper the formation of DOC-pollutant complexes. This mini review is intended to present the importance of DOC quantification and some information on its association with water contaminants, which could render them unavailable for uptake.

Release of heavy metals under pre-set redox potentials in Musa estuary sediments, northwestern of Persian Gulf

Sediments are capable of adsorbing and desorbing heavy metals (HMs) under various environmental conditions. This study investigated the impact of pre-set redox potential (Eh) on the release dynamics of HMs (Co, Cr, Cu, Ni, Pb, V, and Zn) from sediment in an automated biogeochemical microcosm. The release of Co, Pb, and V under reducing conditions increased that may increase the potential risks in the aquatic environment. This phenomenon could be attributed to the decrease in pH, the reductive dissolution of FeMn oxides, and the complex of HMs with dissolved organic carbon (DOC). However, the soluble Cr, Cu, Ni, and Zn decreased at redox potentials as low as -150 mV. Co, Ni, Pb, and Zn were observed in mobile fractions while Cu primarily existed in the residual fraction (indicating lithogenic source). HPI and HEI indexes showed that water quality concerning HMs would become more unsuitable for aquatic life by reducing Eh.

Distribution and source of heavy metals in the sediments of the coastal East China sea: Geochemical controls and typhoon impact

The present study conducted a comprehensive study on the distribution and source of heavy metals (Cu, Zn, Ni, Pb, Cd) in the sediments of the coastal East China Sea (ECS), one of the most developed regions in China with very active land-sea interactions, using 119 surface sediment samples and a 2-m sediment core collected after super Typhoon Chan-hom in 2015. Heavy metals in the surface sediments exhibited metal-dependent and regional distribution patterns, showing higher levels in the southern inner shelf (SIS) than the Yangtze River estuary (YRE), and generally being evaluated as unpolluted to moderately polluted in the coastal ECS (except few sites adjacent to Xiangshan Harbor were strongly polluted by Cd). Based on the organic carbon isotope compositions (δ¹³C) data as well as the strong correlations between heavy metals and natural major elemental contents (Al₂O₃, Fe₂O₃, and SiO₂), we suggest natural weathering detritus as the major source of heavy metals in the YRE region and the spatial distributions were highly controlled by sediment grain size and organic matter. In contrast, the spatial distributions of heavy metals in the SIS region were less correlated with sediment properties, due to more complex sources and stronger hydrodynamic impacts. The vertical distribution of heavy metals in the sediment core indicated significant enrichments since 1950s, but showed unusual gradually decreasing trends in top layer (30 cm-0.5 cm), attributing to the strong disturbance of super Typhoon Chan-hom on sediment transportation and metal partitioning. Besides, we also observed that heavy metal levels in shallow water regions of Zhejiang coast were reduced due to the passage of typhoon. Such strong impacts of super Typhoon Chan-hom on heavy metal distributions in the ECS indicates that the impacts of extreme hydrodynamic events should raise more concern when assessing the distribution and potential risks of contaminants in coastal regions.

Spatio-temporal variations of sedimentary metals in a large suburban lake in southwest China and the implications for anthropogenic processes

Environment quality of suburban and urban lakes receives special attention due to their great impacted by human perturbations and important roles in ecosystem services. Herein, the spatio-temporal variations of 10 metal and metalloid elements in 13 sediment cores from a large suburban lake (Dianchi) were studied to explore the changes in sedimentary environment and pollution and their associations with human activities since the last century. Concentrations of each element were largely varied at spatial scales, but showed similar vertical trends among the profiles, suggesting comparable changes in sedimentary processes in each lake region. Cluster analysis showed two groups of elements: group I includes Al, Ti, Cu, Cr and Ni, and group II includes As, Cd, Hg, Pb and Zn. Temporally, concentrations of all elements were generally constant until the 1950s. Thereafter, group I elements along with the clay percentage started to decrease, indicating accelerated input of coarser soils due to strengthening human perturbation and changing land use. However, group II elements showed increasing values of concentrations, particularly the enrichment factors (EF = 1.0-10.8), which peaked between mid-1990s and 2000, indicating continued pollutants input with watershed economic development. With the implementation of environment management measures, pollution was initially restrained or reduced in recent decades as indicated by the stable EFs and sedimentary fluxes of Cd, Hg, Pb and Zn and decreasing values of As. Spatially, the stocks of anthropogenic As, Cd, Hg, Pb and Zn were higher in the northern while lower in the southern lake area. This spatial difference was mainly due to the large input of industrial and domestic wastewaters in the northern compared to the area in the southern that receives runoff from agricultural and forested land. Overall, the spatio-temporal patterns in accumulation of metal and metalloid elements in the lake reliably reflected the impacts of watershed human activities.