Behaviour Of Trace Metals Research Articles

Trace metal speciation trends in Mazowe dam, Zimbabwe, a typical sub-tropical dam ecosystem impacted by gold mining and agriculture.

The present study aimed to assess trace metal speciation trends in the water and sediments of Mazowe Dam, a typical sub-tropical dam ecosystem impacted by gold mining and agriculture in Zimbabwe. The elements studied include Al, As, Cd, Co, Cr, Cu, Hg, Fe, Mn, Ni, Pb, and Zn. Elemental speciation in the water column was determined using Visual MINTEQ version 3.1 geochemical computer modelling, while speciation in the sediment phase was determined using sequential extraction techniques. For each element, the data obtained were subjected to extensive correlation analysis to identify intra- and inter-metal species interactions in the water column and the sediment phase, as well as across the water-sediment interface. Possible mechanisms to account for the observed species interactions are proposed. In the water column, Co was predicted to have the highest number of chemical species (9), Cd and Zn (8), Mn and Fe (7), Ni (6), Pb (5), Al and Cu (3), Cr, Hg, and As have the least (2). In the sediment, Al, As, Co, Cr, Cu, Fe, Ni and Fe mainly exist in the residual fraction, while Zn and Mn concentrations in fractions vary per sampling site, with no fraction that is dominant across the sampling sites. Equilibrium exchange reactions across the water-sediment interface were observed e.g., for Cd species /FA2Cd (aq) and Co species /FACo+2G (aq), and /FA2Co (aq). This study is valuable in highlighting trace metal speciation in a tropical dam ecosystem in Africa and adds to the growing knowledge about the behaviour of trace metals in aquatic ecosystems in the region and globally.

Characterization and spatiotemporal variations of fluorescent dissolved organic matter in leachate from old landfill-derived incineration residues and incombustible waste.

Dissolved organic matter (DOM) influences the bioavailability and behavior of trace metals and other pollutants in landfill leachate. This research characterized fluorescent dissolved organic matter (FDOM) in leachate from an old landfill in Japan during a 13-month investigation. We employed excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor analysis (PARAFAC) to deconvolute the FDOM complex mixture into three fluorophores: microbial humic-like (C1), terrestrial humic-like (C2), and tryptophan-like fluorophores (C3). These FDOM components were compared with findings from other studies of leachate in landfills with different waste compositions. The correlations among EEM-PARAFAC components, dissolved organic carbon (DOC) concentration, and ultraviolet-visible and fluorescence indices were evaluated. The FDOM in leachate varied spatially among old and extended leachate collected in the landfill and leachate treatment facility. The FDOM changed temporally and decreased markedly in August 2019, November 2019, and April 2020. The strong positive correlation between HIX and %C2 (r = 0.87, ρ = 0.91, p < 0.001)) implies that HIX may indicate the relative contribution of terrestrial humic-like components in landfill leachate. The Fmax of C1, C2, and C3 and the DOC concentration showed strong correlations among each other (r > 0.72, ρ > 0.78, p < 0.001) and positive correlations with leachate level (r > 0.41, p < 0.001), suggesting the importance of hydrological effects and leachate pump operation on FDOM.

Salinity-Induced Changes in Heavy Metal Behavior and Mobility in Semi-Arid Coastal Aquifers: A Comprehensive Review

Semi-arid coastal aquifers face critical challenges characterized by lower rainfall, higher evaporation rates, and looming risk of over-exploitation. These conditions, coupled with climate change, are conducive to seawater intrusion and promote mechanisms associated with it. The understanding of metal behavior in such environments is limited, and hence, an attempt is made through this review to bridge the knowledge gap. A study on the behavior of trace metals within a specific context of semi-arid coastal aquifers was carried out, and 11 aquifers from 6 different countries were included. The review observed that trace metals within semi-arid coastal aquifers exhibit distinctive behaviors influenced by their surrounding environment. The prevalence of evaporation and continuous seawater intrusion played a pivotal role in shaping trace metal dynamics by curtailing groundwater flux. The findings suggest that the formation of stable Cl and organic ligands under increased alkaline conditions (pH &gt; 8) has higher control over Zn, Pb, and Cd toxicity in a highly ionic reactive condition. In addition, dominant control of Fe/Mn-hydroxide association with Pb and high organic affinity of Zn played a pivotal role in controlling its bioavailability in aquifers such as WFB, Saudi Arabia NW-C and India. On the contrary, under prevailing acidic conditions (pH &lt; 6), carbonate and SO4-ligands become more dominant, controlling the bioavailability/desorption of Cu irrespective of its origin. The behavior of Ni is found to be controlled by stable organic ligands increasing salinity. An increase in salinity in the considered aquifers shows an increase in bioavailability of Ni, except UmC, South Africa, where organic ligands act as a sink for the metal, even at low pH conditions (pH &lt; 5.5). This study indicates that factors such as mineral saturation, carbonate complexes, pH variations (pH &gt; 8), and chloride complexes govern the distribution of trace metals further enhanced by prolonged water residence time. Nonetheless, specific conditions, such as a reducing and acidic environment, could potentially elevate the solubility of highly toxic Cr (VI) released from anthropogenic sources.

Behavior of trace metals in sedimentary cores from marine and lacustrine environments in Algeria

Behavior of trace metals in sedimentary cores from marine and lacustrine environments in Algeria

Speciation studies at the Illite - solution interface: Part 1 – Sorption of phosphate ions

Although phosphate ion (hereafter “P”) sorption is known to influence clay surface reactivity and trace metal behavior in the environment, there is still a lack of in situ spectroscopic evidence on the identity of phosphate sorption species formed at the interface between solution and clays with a 2:1 layered structure (2 silica tetrahedral: 1 octahedral layers), which are ubiquitous in soils and clay formations. We studied the surface speciation of phosphate ions by in situ spectroscopic monitoring along P sorption at the interface between a solution and a homoionic Na-illite, as a function of time or aqueous phosphate concentration (20–250 µM) leading to low/moderate P surface coverage. We also combined them with batch sorption experiments and electrophoretic mobility (EM) measurements. Macroscopic data indicated that the percentage of P sorption depends on pH, aqueous phosphate concentration, and the clay/solution ratio of the experiment, i.e., the coverage of the clay surface by P, with a maximal sorption capacity of the clay equal to ca. 6 µmol.g−1 at pH 4. Macroscopic and EM data further suggest that P sorption mechanisms onto illite confer negative charges on the surface and involve several sorption species and/or surface sites present on the clay edges. In situ FTIR spectra showed that, at acidic pH, three types of phosphate surface species exist at the illite-solution interface: an outer-sphere surface complex (OSSC) of phosphate (ΞSOH2+…H2PO4-, with S referring to a sorption site on the clay), an inner-sphere surface complex (ISSC) of phosphate, probably a monodentate binuclear surface complex ((ΞSO)2PO2) formed by surface ligand exchange with high-affinity aluminol sites and, to a lesser extent, low-affinity sites on the clay edges, and, in limited amounts, an Al-phosphate surface precipitate. Phosphate ion sorption occurs through the initial formation of the OSSC of phosphate, which dominates phosphate surface speciation at short reaction times and low P concentrations and transforms over time into the ISSC of phosphate. This study presents the first published in situ surface speciation of phosphate ions sorbed at the interface between a solution and an illite. The evidence of a strong sorption of phosphate ions at this clay surface provides new and sound knowledge to better understand the environmental fate of phosphate ions and trace metals, particularly in agricultural soil - groundwater continua or in clay host rocks considered for high-level radioactive waste disposal.

An evaluation of spatial and seasonal distributions of dissolved trace metals in the water of the natural wetlands

The spatial and temporal distributions of trace metals in dissolved forms mainly result from anthropogenic and lithogenic contributions. Surface water samples (∼0.5 m) were collected monthly at respective stations from Setiu Wetland. In this study, the behaviour of trace metals in the dissolved phases along the water column from sampling sites in the Setiu Wetland, Malaysia was investigated. In addition, dissolved organic carbon (DOC) and physical parameters such as salinity, temperature, pH and dissolved oxygen (DO) of the surface water were measured in order to evaluate the relationship between trace metals fractionation with different water quality parameters. Size fractionation study of dissolved trace metals using ultrafiltration technique were also carried out and analysed using inductively coupled plasma mass spectrometry (ICP-MS). Correlation of trace metals with other measured parameters was made to furthermore understand the dynamics of trace metals and its fractionated components in this area. The concentration of dissolved trace metals was in the range of 0.001–0.16 μg/L for Cd, 0.12–2.81 μg/L for Cu, 0.01–1.84 μg/L for Pb, 3–17 μg/L for Fe and 1–34 μg/L for Zn, suggesting the input of anthropogenic sources for trace metals such as municipal, industrial, agricultural and domestic discharge. The periodic monitoring and evaluation of trace metals in wetlands and protected tropical areas is highly recommended.

Microplastics and trace metals in river sediment: Prevalence and correlation with multiple factors

Microplastics (MPs), which are ubiquitous, are no longer novel emerging pollutants, yet our knowledge of them is insufficient. This study investigates the prevalence of MPs and trace metals in sediment belonging to Ma River, Vietnam, and their interaction with various parameters, including nutrients such as total carbon (TC), total nitrogen (TN), and total phosphorus (TP), grain sizes, and MPs in surface water. The study revealed that the abundance of MPs in sediment (MPs/S) is relatively high (i.e., 1328.3 ± 1925.5 items.kg−1 dry weight), while the concentration of MPs in surface water (MPs/W) was relatively low (i.e., 57.3 ± 55.8 items.m−3) compared to other areas. Notably, the study found that arsenic and cadmium concentrations exceeded baseline levels, indicating their anthropogenic origin. To interpret the relationship between MPs/S, metals, and the aforementioned parameters, principal component analysis and Pearson correlation analyses were employed. The results demonstrated a significant correlation between metals and nutrients, as well as small grain sizes such as clay and silt. It was observed that the majority of metals displayed co-occurrence with one another but showed weak associations with the levels of MPs present in both water and sediment. Additionally, a weak correlation was observed between MPs/W and MPs/S. In conclusion, these findings suggest that the distribution and behavior of MPs and trace metals in aquatic systems are influenced by multiple factors, including nutrient levels, grain size, and other chemical and physical characteristics of the environment. While certain metals may have natural sources, others may result from human activities such as mining, industrial discharge, and wastewater treatment plants. As a result, understanding the sources and aspects of metal contamination are critical for determining their relationship with MPs and developing effective strategies for mitigating their impact on aquatic ecosystems.

Behavior of trace metals during composting of mixed sewage sludge and tropical green waste: a combined EDTA kinetic and BCR sequential extraction study in New Caledonia.

The aim of the study was to assess the impact of composting on the release dynamics and partitioning of geogenic nickel (Ni), chromium (Cr)and anthropogenic copper (Cu) and zinc (Zn) in a mixture of sewage sludge and green waste in New Caledonia. In contrast to Cu and Zn, total concentrations of Ni and Cr were very high, tenfold the French regulation, due to their sourcing from Ni and Cr enrichedultramafic soils. The novel method used to assess the behavior of trace metals during composting involved combining EDTA kinetic extraction and BCR sequential extraction. BCR extraction revealed marked mobility of Cu and Zn: more than 30% of the total concentration of these trace metals was found in the mobile fractions (F1 + F2) whereas Ni and Cr were mainly found in the residual fraction (F4). Composting increased the proportion of the stable fractions (F3 + F4) of all four trace metals studied. Interestingly, only EDTA kinetic extraction was able to identify the increase in Cr mobility during composting, Cr mobility being driven by the more labile pool (Q1). However, the total mobilizable pool (Q1 + Q2) of Cr remained very low, < 1% of total Cr content. Among the four trace metals studied, only Ni showed significant mobility, the (Q1 + Q2) pool represented almost half the value given in the regulatory guidelines. This suggests possible environmental and ecological risks associated with spreading our type of compost that require further investigation. Beyond New Caledonia, our results also raise the question of the risks in other Ni-rich soils worldwide.

Trace metal fate in soil after application of digestate originating from the anaerobic digestion of non-source-separated organic fraction of municipal solid waste

Introduction: Digestate originating from anaerobic digestion of non-source-separated organic fraction of municipal solid waste (OFMSW) is produced abundantly worldwide and generally discarded in landfills. However, it can be a valuable resource for many bioeconomy strategies as land restoration, only if a consolidated understanding of the contaminants’ presence and behaviour in digestate-amended soil is achieved. This study aimed to investigate the fate of trace metals, namely Zn, Cu, Pb, and Cr found in the digestate, along the soil profile after digestate application on soil, and the influence that other contaminants as pharmaceutical compounds can have on their behaviour in the soil system.Methods: For that, a 90-day soil column experiment was conducted using a fine loamy sand soil topped with a layer of digestate-amended soil. Digestate-amended soil had a soil to digestate proportion of 14 to 1 (dry weight). Two experimental conditions were tested: soil amended with digestate, and soil amended with digestate spiked with the antidiabetic drug metformin. Soil samples were taken at 4 depths on days 1, 7, 21, 35 and 90, and total trace metals concentrations and fractionation were determined via atomic absorption spectroscopy.Results: Results showed that Zn, Cu, Pb ad Cr initially present in the digestate were transferred from the digestate-amended soil layer to the underlying soil layer over time, although in low amounts. Nevertheless, no transfer was detected to the deeper soil layers. Trace metals in soil were predominantly in immobile and less bioavailable forms associated with clay and silicate mineral groups, whereas in the digestate-amended soil they were in more bioavailable forms, which could be related to metals’ migration in the soil layers below. Results also show that the presence of metformin had no influence on trace metal behaviour, giving insight also on possible interactions with other potentially present contaminants as microplastics.Conclusion: The current study showed that OFMSW digestate can be a promising organic nutrient-rich matrix for land restoration even if it may contain high metals’ concentrations because low metal mobility along the soil profile can be expected.

Bayesian-Based Approaches to Exploring the Long-Term Alteration in Trace Metals of Surface Water and Its Driving Forces.

Trace metal pollution poses a serious threat to the aquatic ecosystem. Therefore, characterizing the long-term environmental behavior of trace metals and their driving forces is essential for guiding water quality management. Based on a long-term data set from 1990 to 2019, this study systematically conducted the spatiotemporal trend assessment, influential factor analysis, and source apportionment of trace elements in the rivers of the German Elbe River basin. Results show that the mean concentrations of the given elements in the last 30 years were found in the order of Fe (1179.5 ± 1221 μg·L-1) ≫ Mn (209.6 ± 181.7 μg·L-1) ≫ Zn (52.5 ± 166.2 μg·L-1) ≫ Cu (5.3 ± 5.5 μg·L-1) > Ni (4.4 ± 8.3 μg·L-1) > Pb (3.3 ± 4.4 μg·L-1) > As (2.9 ± 2.3 μg·L-1) > Cr (1.8 ± 2.4 μg·L-1) ≫ Cd (0.3 ± 1.1 μg·L-1) > Hg (0.05 ± 0.12 μg·L-1). Wavelet analyses show that river flow regimes and flooding dominated the periodic variations in metal pollution. Bayesian network suggests that the hydrochemical factors (i.e., TOC, TP, TN, pH, and EC) chemically influenced the metal mobility between water and sediments. Furthermore, the source apportionment computed by the Bayesian multivariate receptor model shows that the given element contamination was typically attributed to the geogenic sources (17.5, 95% confidence interval: 13.1-17.6%), urban and industrial sources (22.1, 18.0-27.2%), arable soil erosion (24.2, 16.4-31.5%), and historical anthropogenic activities (35.2, 32.8-43.3%). The results provided herein reveal that both the hydrochemical influence on metal mobility and the chronic disturbance from anthropogenic activities caused the long-term variation in trace metal pollution.

Novel fluxing strategy of copper matte smelting and trace metals in E-Waste recycling

The distribution behavior of trace metals between copper matte and spinel-saturated iron silicate slags was investigated at 1250 °C and pSO2 of 0.25 atm at low silica concentrations. The experiments were conducted in magnetite (Fe3O4) spinel crucibles in controlled CO-CO2-SO2-Ar gas mixtures using a high-temperature equilibration-quenching technique. The concentrations of trace elements in matte, spinel, and slag were quantified by electron probe X-ray microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. The trace metals (Ag, Ni, Co, and Sn) in all phases and their distribution coefficients were calculated as a function of matte grade. Results show that silver and nickel can be effectively recovered into matte, whereas cobalt and tin are predominantly deported into slag and gas phases, respectively. These results augment the fundamental thermodynamic data of trace metal distributions in copper smelting processes at low-silica fluxing practices.

Early diagenetic behavior of trace metals along with estimation of their diffusive fluxes: Ecological risk assessment in pore water and sediment of Bizerte Lagoon, Tunisia.

Bizerte Lagoon is a vital Mediterranean ecosystem subjected to intense anthropogenic pressure. The potential ecological risk caused by certain metals (Zn, Cu, Cr, Cd, Ni, Pb and Mn) is assessed from the data carried out in the sediment and pore water at two sites along with identifying the effects of diagenetic processes on the vertical distribution of these metals and their resulting diffusive fluxes. Using various ecological indices our results reveal a high ecological risk to benthic organisms from metals chiefly Cd, Pb and Ni accumulated in the sediment at both sites. Metals derived from organic matter degradation (Cu and Cd) and/or reduction of Mn-Fe-oxyhydroxydes (Pb, Ni, Zn, Cr) due to early diagenetic processes in sediment. The resulting concentration gradients between pore water and overlying water induce diffusive fluxes of metals to the water column. The estimation of the potential ecological risk caused by dissolved metals in pore waters by application of the Interstitial Water Criteria Toxic Units index indicates a slight ecological risk by Cu that was not identified in sediment. The ecological risk posed by dissolved metals is evidenced from -6 cm depth, which reduces the possibility of contamination of benthic species living above the water-sediment interface by diffusive fluxes of these metals.

Contamination and health risks of trace metals in water and sediments of May Sieley stream, Ethiopia

The Stockholm Convention underpins the significance of monitoring the toxic trace metals in ecosystems. This study was conducted in May Sieley stream, North Ethiopia, in 2020. The main aim was to assess the spatial-temporal variation of trace metals in water and sediments using the ICP-OES technique and further evaluate their health risks. PCA and correlation analysis identified the sources of pollution, mutual dependence, and identical behavior of trace metals. Except for Hg, the Cu, Zn, Ni, As, Cr, Cd, and Pb were high in water during the post-rainy season. The trace metals concentrations were lower in dry season sediment than in post-rainy season except for Cu and Zn. The post-rainy season showed a higher upstream concentration than the rest. There was a strong positive correlation (0.84 < r < 0.93, p < 0.01) between Ni–Cr–Cd–Pb, suggesting that the same factors influenced these trace metals. Hg correlated negatively with all other trace metals suggesting that this trace metal tends to move in a different direction. The water's Cr, Cd, Pb, and As exceeded WHO standards during the post-rain season. However, Hg and As exceeded those standards in the dry season. Pb, As, Cd, and Hg showed unacceptable non-carcinogenic levels in both groups (Q > 1). All trace elements assessed displayed unacceptable carcinogenic risk levels in both groups. The findings are significant to the policymakers in framing water quality control strategies at the river basin level.

Controls on the mineralogical and geochemical dispersion in soil and water around a tailing storage facility in the epithermal gold–silver mine in Central Kalimantan, Indonesia

The mineralogical and geochemical parameters on soil, waste, and tailings are major components for water quality assessments because they dictate the behavior of the chemical composition and water–rock interactions. Arsenic and trace metal contamination occasionally occurs because of the oxidation of arsenic-rich minerals and hydrothermal alteration or because of anthropogenic influences, such as industrial mining activity. This study aimed to understand the characteristics of tailings, soils, surface water, and groundwater to evaluate the possible geochemical dispersion of metals employed in tailing storage facilities. A study site at the former epithermal Au–Ag mine in Central Kalimantan, Indonesia, was selected because it was suitable for investigating the geochemical behavior of trace metals in water and solid samples and their possible contribution to metal contamination in tropical regions. A detailed study of the tailings comparing mineralogical and geochemical analysis indicates that the presence of unaltered, intermediate, and oxidized zone within the tailings can be related to the sulfides alteration indices (SAI). These zones include an unoxidized zone in the submerged areas where sulfides, including pyrite with less sphalerite and galena, remain fresh. In the intermediate zone, pyrite starts to change to iron oxyhydroxide. The SAI parameters from the intermediate zone, extending 50 cm below the tailing surface, indicate that only a few grains of pyrite in this zone are weakly altered and are capped by a thin (<10 μm) iron oxyhydroxide. The oxidized zone is indicated by traces of remaining pyrite and iron oxyhydroxide as the primary mineral. Heavy metals and rare earth elements from tailings storage facilities were scavenged from the soil solutions by groundwater. The stable isotopes of oxygen, hydrogen, and dissolved rare earth elements (REEs) were used as natural tracers in systems affected by acid mine drainage. The results showed that stable isotope and rare earth elements data do not support contamination between the surface and groundwater. This study found that the oxidation of ferrous iron to ferric ion and precipitation of Fe-oxyhydroxides in soil and water has a close spatial relationship with rare earth elements, which are concentrated only in intermediate and oxide zones.

Spatial and Temporal Distribution and Influencing Factors of Dissolved Trace Metals in Jiulong River Estuary and Xiamen Bay

Trace metals play an important role in some biogeochemical processes in the marine system. The physical and hydrological conditions in estuaries and coastal seawater are complicated and significantly affected by human activities. Therefore, the biogeochemical behavior and influencing mechanism of trace metals in nearshore water have become a research hotspot. Jiulong River estuary and Xiamen Bay are located in the coastal areas of Fujian Province, which are significantly influenced by Longyan, Xiamen, and Zhangzhou City. In July 2021, November 2021, and January 2022, the trace metals chromium (Cr), manganese (Mn), cobalt (Co), nickel (Ni), copper (Cu), and cadmium (Cd) and environmental factors (water temperature, salinity, pH, dissolved oxygen (DO), suspended particulate matter (SPM), etc.) in Jiulong River estuary and Xiamen Bay were investigated. The results showed that the order of trace metal concentration average values measured in Jiulong River estuary and Xiamen Bay was Mn>Ni>Cu>Cr>Co>Cd. In July 2021, the average values of ρ(Cr), ρ(Mn), ρ(Co), ρ(Ni), ρ(Cu), and ρ(Cd) were 0.159, 47.96, 0.068, 1.56, 1.07, and 0.016 μg·L-1, respectively. In November 2021, the average values were 0.216, 8.48, 0.030, 1.70, 1.92, and 0.019 μg·L-1, respectively. The average concentrations in January 2022 were 0.281, 32.39, 0.062, 2.21, 1.54, and 0.034 μg·L-1, respectively. The concentration of dissolved metals in the estuary was higher than that in the bay area. Principal component analysis showed that the main factors affecting the concentrations of dissolved trace metals were river runoff and anthropogenic activities.

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.

Risk assessment and spatio-temporal distribution of dissolved trace metals in Swarna, Sharavati and Kali estuaries, South-West Coast of India

Trace metals act as a limiting nutrient and prerequisite for primary productivity in marine environments. The distribution of metals in dissolved phase along the salinity gradients of Swarna, Sharavati and Kali estuaries in southwestern India, during post and pre-monsoon seasons, were studied. We have investigated the behaviour of trace metals in the estuarine environment and their extent of impact on human health and ecosystem. The study revealed, non-conservative behaviour of dissolved Mn, Fe, Ni, Cd and Co in the estuaries. Whereas Cu behaved non-conservatively in post-monsoon and conservatively in pre-monsoon seasons. Risk assessment studies revealed that higher chronic daily intake (CDI) in humans, through dermal pathway, in Swarna and Sharavati estuaries during post-monsoon, whereas it was during pre-monsoon season in the Kali estuary. Hazard Index values for the studied metals in adults and children are below risk thresholds, though children are more prone to health risk through the dermal pathway.

Potential impacts of titanium dioxide nanoparticles on trace metal speciation in estuarine sediments

Engineered titanium dioxide (TiO2) nanoparticles (NPs) are widely used and consequently released into the environment. The subsequent accumulation of TiO2 NPs in depositional environments may affect the geochemical behavior of trace metals, which needs to be assessed. Here, we performed experiments to investigate the speciation change for molybdenum and tungsten in the presence of TiO2 NPs. Laboratory results show that the rate constant for MoS42− hydrolysis associated with TiO2 NPs is ~1.75 × 10−9 L m−2 s−1, whereas it is 5.95 × 10−10 L m−2 s−1 for WS42− hydrolysis. In addition, we estimated the maximum rate for MoS42− hydrolysis to be ~1.24 × 10−1 μM hr−1, whereas the maximum rate for WS42− hydrolysis is ~4.91 × 10−2 μM hr−1. However, the modeling results suggest that the TiO2 NPs accumulated in estuarine sediments might play a relatively minor role in affecting the speciation of trace metals prior to the current time. This is because the relatively low accumulation (i.e., < 8 × 10−3 mol kg−1) of TiO2 NPs before 2021 results in the lower rate (>100 times) for speciation changes of both molybdenum and tungsten compared to the rate for natural geochemical processes. On the other hand, our results suggest that TiO2 NPs will likely impact the oxyanion cycling in the near future owing to the increasing accumulations of TiO2 NPs in estuarine sediments.

Vertical changes in the geochemical distributions of iron, manganese and heavy metals in wetland soil cores from cold temperate zones in northeastern China

Pedogenic processes influence the geochemical distributions of elements in soils. Such knowledge, however, is lacking on wetland soil in the cold temperate zone of northeastern China. Two wetland soil cores were collected, sliced at 5 cm intervals, and analyzed for pH, soil organic matter (SOM), Al, Fe, Ti, Mn, Co, Cr, Cu, Ni, and Pb. The results showed that the wetland soil cores were characterized by acidic pH levels, SOM accumulations in the A horizon, eluviation of Fe and Mn from the A and E horizons, and their illuviation in the B horizon. The heavy metals, Co and Pb, were leached from the A and E horizons and subsequently accumulated in the B horizon during pedogenic processes, while Cr, Cu, and Ni might not have migrated significantly. The average Co and Pb concentrations in the B horizon were 47.6 and 70.4 mg kg−1, respectively, which were several times higher than those in the A and E horizons. In the B horizon, five heavy metals, especially Co and Pb, preferentially partitioned in the Fe/Mn oxide phase (e.g., 45.4%, 27.5%, 9.4%, 8.3%, and 7.3% for Co, Pb, Ni, Cr, and Cu, respectively), following the residual phase. In the A and E horizons, however, these metals preferentially partitioned into different mineral phases (e.g., the Fe/Mn oxide phase for Co, organic matter phase for Cr and Cu, Fe/Mn oxide and organic matter phases for Ni, and carbonate and Fe/Mn oxide phases for Pb) following the residual phase. Therefore, pedogenic processes influenced the vertical distributions of both the heavy metal concentrations and their chemical forms in the wetland soil of cold temperate zones. This work provides insights into the behavior of major and trace metals in the soil depth profiles of seasonally waterlogged and freezing-thawing wetland soils.

Binding characteristics of copper onto biochar-derived DOM using general, heterospectral and moving-window two-dimensional correlation analyses

Dissolved organic matter released from biochar (biochar-derived DOM, BDOM) could dominate the environmental behavior and fate of trace metals by forming BDOM-metal complexes. Here general, heterospectral as well as moving-window (MW) two-dimensional correlation spectroscopy (2DCOS) analyses of synchronous fluorescence and Fourier transform infrared spectra were employed to explore the heterogeneous binding characteristics between sludge BDOM and Cu(II). The results revealed that Cu-BDOM binding first occurred in the fulvic-like (368–380 nm), then humic-like (428 nm) fluorescent fractions, followed by infrared groups of phenolic hydroxyl groups, carboxylate, COH of polysaccharide groups, CC of aromatic carbon, CH of aliphatics and COC of aliphatic ethers. The binding affinity of the hydrophilic groups was stronger than that of hydrophobic groups in BDOM towards Cu(II). Fluorescence components in BDOM played a decisive role in the binding of Cu(II) with trace concentration (1 μM), while infrared functional groups made a substantial contribution in the complexation of Cu(II) with higher concentration (10–100 μM). The concentration of final configuration transformation point (11.7 μmol/mg in this study) by MW2DCOS analysis was suggested as an actual binding threshold that was helpful for evaluating their environmental behaviors.