Fate Of Metals Research Articles

Fates of heavy metals, S, and P during co-combustion of textile dyeing sludge and cattle manure

The co-combustion of textile dyeing sludge (TDS) and cattle manure (CM) may enhance circularity in terms of resource and pollution controls. However, the pollutant migrations and transformations of ashes and their characterization during the co-combustion are still unclear. This study aimed to quantify the transformation and migration behaviors of the co-combustion ashes, as well as the interactions involved via thermogravimetric experiments and thermodynamic simulations. The addition of TDS facilitated the conversions of Ni and Cr from the extractable form to the stable one, increasing their environmental safety. P dominated S for the reaction with Ca which promoted the generation of S-containing gas emission and apatite P. The reactions between the minerals in CM and Ca in TDS generated calcium silicate, decreasing the S-fixation ability of Ca, while increasing the emission of S-containing gases. Our findings provide insights into the interactions among the minerals, the heavy metals, and the specific elements and their impacts on pollutant emissions, thus enhancing pollution control strategies.

Processing of coal gasification fine slag by different physical separation methods: Fate of typical heavy metals and comparison analysis on products

The separation of carbon-mineral components in coal gasification fine slag (CGFS) is an important prerequisite for achieving large-scale utilization of the CGFS resources. This study aims to reveal the influence of three physical separation methods on the distribution features, occurrence modes, and environmental risk of typical heavy metals (i.e., V, Cr, Mn, Ni, Cu, Zn, Ba, and Pb) in the CGFS. The results show that all three physical separation methods can separate carbon-rich or mineral-rich fractions from the CGFS at different enrichment levels. Thereinto, froth flotation has a high balance between high yields and excellent separation performance. Furtherly, Ni, Cu, Zn, and Pb are more concentrated in the two carbon-rich fractions obtained by froth flotation while other heavy metals are mostly enriched in the mineral-rich fractions. Density separation is possible to obtain carbon-rich fractions with a fairly high fixed carbon content (68.29 %, dry basis). In addition, a rough separation of the carbon-mineral fractions in CGFS can be performed by particle size classification. The various concentrations and distribution features of typical heavy metals in different separated products are associated with their specific structures. The carbon particles derived through the froth flotation have a higher specific surface area than those produced from the density separation and size classification. It is found a high correlation between mineral content and typical heavy metal concentrations, while porous carbon particles with a high specific surface area and particle size effect could reduce the dependence of some heavy metals (e.g., semi-volatile or volatile heavy metals Ni, Cu, Zn, and Pb) concentrations on mineral content. In addition, the typical heavy metals in separated fractions with a high content carbon particles as well as small-sized particles tend to have a high proportion of mobile fractions. Moreover, the eco-risk assessment code (RAC) analysis results indicate that priority attention should be given to the potential environmental impacts of Mn, Ni, Cu, Ba, and especially Zn in high-carbon content products and small-sized fractions during their resource utilization process.

Occurrence, Fate, and Implications of Heavy Metals during Anaerobic Digestion: A Review

Over the years, anaerobic digestion (AD) has evolved as a competent technology to retrieve energy potential from various organic substrates, including wastewater. However, the energy metabolisms of anaerobic microorganisms, biochemical reactions, and biogas production are affected by various parameters, including heavy metals. It is important to understand the interaction of heavy metals with anaerobes and their potential influence on the process to enhance energy potential. This review methodically outlines the occurrence and role of heavy metals in the AD process. Additionally, the repercussions of the most common heavy metals (i.e., Cu, Zn, Cd, Fe, and Ni) on each stage of AD (i.e., hydrolysis, acidogenesis, and methanogenesis) have been discussed. We found that traces of heavy metals can endorse anaerobic digestion, but inhibition increases with increasing concentration. Methanogenic archaea are more susceptible to heavy metal inhibition than hydrolytic and acidogenic archaea. An improved understanding and relevant intuition will help to promote biogas production along with heavy metal management.

Applying synchronous fluorescence spectra with Gaussian band fitting and two-dimensional correlation to characterize structural composition of DOM from soils in an aquatic-terrestrial ecotone

Dissolved organic matter (DOM), the primary participant of carbon and nitrogen cycle, has a great impact on the behavior and fate of organic pollutants and heavy metals in eutrophic lakes. The dynamic spectral properties of DOM fractions were revealed in an aquatic-terrestrial ecotone under the different types of land use. Composite soil samples of different depths (0–20, 20–40 and 40–60 cm) were collected from four different land uses along a disturbed-impact gradient in Taihu Lake, China, i.e., grassland (GRL), forest land (FOL), paddy field (PAF), and vegetable field (VEF). DOM mainly consisted of tyrosine-like material (TYLF), tryptophan-like material (TRLF), microbial humic-like material (MHLF), fulvic-like material (FLF) and humic-like material (HLF) within all soil profiles, where TRLF was the dominant component (61.30 %) using synchronous fluorescence spectroscopy (SFS) combined with principal component analysis and Gaussian band fitting. Based on two-dimensional correlation spectroscopy with SFS and Fourier transform infrared, the variation order of DOM fractions was FLF → MHLF → HLF → TRLF → TYLF within the GRL soil profile, and MHLF exhibited an oppositive change with aliphatic OH and amide I in protein. The order of DOM fractions was MHLF → FLF → HLF → TYLF → TRLF within the FOL soil profile, and the change trend of MHLF remained oppositive with aliphatic OH and CO in ester. The order of DOM within the PAF soil profile fractions was TRLF → MHLF → HLF → TYLF → FLF, and changing trends of TYLF were oppositive to aliphatic OH, CH bending vibration, CH bending vibration and CO in ester. The order of DOM fractions was HLF → TYLF → TRLF → FLF → MHLF within the VEF soil profile, where the changing trend TYLF remained oppositive to aliphatic OH, CH deformations in lignin and aliphatic group and amide I in protein. This study may provide important support for alleviating lake water eutrophication or pollution.

Computational modelling of geochemical speciation of the trace metals in the wastewater treatment process optimization

The speciation of trace metals in the wastewater treatment plants determines its ultimate fate in natural surface waters due to biological and chemical processes. The quantification of the trace metals speciation studies was undertaken in the WWTP and was of special concern due to their persistence and recalcitrance in the biosphere. The metals of interest included: Al, Co, Cr, Cd, Fe, Cu, Ni, Mn, Mo, Zn, Pb and Ti. Trace metals accumulation was determined using geochemical modelling-mass balance. The mass balance model had a numerical impact on cost optimization procedure that uses steady state with a set of pre-defined constraints to evaluate operation points, controller parameters and plant dimensions. The mass balance model allowed detection of inconsistencies within the trace metals datasets and assisted in identifying the systematic errors in the metal reduction. It quantified the overall removal and fate of trace metals in biological treatment plants. Mass balances comprising seasonal programmable sampling showed a significant reduction in the number of trace metals. Removal of metals from biological treatment processes was mainly by complexation of the metals with microorganisms, precipitation and adsorption. The comparison of the measured data indicated an increasing trend of high concentration in the sludge (biomass) that could be of danger to human health and environment. Geochemical modelling and computation of the speciation of the trace metals offer a powerful tool for the process design, troubleshooting and optimization representing a multi-variable system that cannot be effectively handled without appropriate computer-cased technique and modelling.

Applying EEM-PARAFAC combined with moving-window 2DCOS and structural equation modeling to characterize binding properties of Cu (II) with DOM from different sources in an urbanized river

Dissolved organic matter (DOM) in aquatic environment distinctly affects the behavior and fate of heavy metals via complexation, while the interfacial mechanisms and processes are still lacking in detail. Here, Cu (II) binding characteristics of DOM originated from hilly (NDOM), rural (RDOM) and urban (UDOM) regions in an urbanized river was explored by fluorescence excitation-emission matrix spectroscopy (EEM) combined with principal component coefficients, parallel factor analyses (PARAFAC), moving-window two-dimensional correlation spectroscopy (MW2DCOS) and structural equation modeling (SEM). Eight components were extracted from the titrants through EEM-PARAFAC, i.e., phenol-like substance (C1), tyrosine-like substance (C2), visible tryptophan-like substance (C3), ultraviolet tryptophan-like substance (C4), recent biological production (C5), wastewater-derived organic matter (C6), microbial humic-like substance (C7) and fulvic-like substance (C8). Interestingly, NDOM only contained C1, C3, C5 and C8, while nearly all components were found in RDOM (except for C2) and UDOM (except for C4). The f value of C1 (1.239) in NDOM was much higher than those in RDOM (0.134) and UDOM (0.115), so was of C8. It indicated that phenol-like and fulvic-like derived from autochthonous sources exhibited great binding ratios in the complexation with Cu (II). Moreover, C3 and C5 from UDOM exhibited higher f values (0.591 and 1.983) than those from NDOM and RDOM, suggesting that Cu (II) has a great binding capacity on protein-like from domestic and industrial wastewater. The MW2DCOS revealed that phenol-like and protein-like in NDOM and RDOM were essential for the binding of 160 μmol L−1 Cu (II), whereas fulvic-like in NDOM and UDOM could react significantly with 10 μmol L−1 Cu (II). Based on SEM, Cu (II) concentration had a negative direct effect on the fluorescence intensity of C7 or C8, whereas it showed an indirect positive effect on C7 or C8 through influencing C5, so was C6. It suggested that Cu (II) showed an indirect positive effect on the C8. This study might present a further comprehend of the environmental behaviors of Cu (II) in rivers.

Impacts of climate change on metal leaching and partitioning for submarine mine tailings disposal.

At present, there are no standardised tests to assess metal leaching during submarine tailings discharge. In this study the influence of variables known to affect metal mobility and availability (dissolved organic carbon (DOC), pH, salinity, temperature, aerated/anoxic conditions) along with variables affected by the discharge conditions (flocculant concentration, suspension) were studied in bench-scale experiments. The leaching tests were developed based on the case of a copper mine by Repparfjorden, northern Norway, which is planned to re-open in 2022. The experiments, which had three week duration, revealed low (<6%) leaching of metals. Multivariate analysis showed that all variables, apart from DOC, highly influenced leaching and partitioning of at least one metal (Ba, Cr, Cu, and/or Mn). The high quantity of the planned annual discharge of mine tailings to the fjord (1-2milliontonnes) warranted estimation of the leached quantity of metals. Multivariate models, using present-day conditions in the fjord, estimated leaching of up to 124kg Ba, 154kg Cu and 2400kg Mn per year during discharge of tailings. Future changes in the fjord conditions caused by climate change (decreased pH, increased temperature) was predicted by the multivariate models to increase the leaching up to 55%, by the year 2065. The bench-scale experiments demonstrated the importance of including relevant variables (such as pH, salinity, and temperature) for metal leaching and -partitioning in leaching tests. The results showed that metal leaching during discharge is expected and will increase in the future due to the changed conditions caused by the foreseen climate change, and thereby underline the importance of monitoring metal concentrations in water during operations to determine the fate of metals in the fjord.

Performance of graphene and traditional soil improvers in limiting nutrients and heavy metals leaching from a sandy Calcisol

Given the large amount of Graphene produced in the last years, there is the need to introduce this new material into a green and circular economy loop. In this study, for the first time, the fate of nutrients and heavy metals in a sandy Calcisol amended with Graphene was monitored and compared to other traditional improvers such as Compost, Zeolites, and Biochar. This was performed via saturated and unsaturated columns' experiments with two different fertilization regimes: one with NPK fertilizer and one with an innovative fertigation water (FW) produced from a pilot wastewater treatment plant. The breakthrough curves of each nutrient and heavy metal were analysed to understand the main processes occurring in saturated and unsaturated conditions, comparing the columns amended with the improvers versus the unamended Controls. Mass balances for each nutrient and heavy metal were developed to infer whether the different soil improvers were effective in minimizing leaching. Graphene, for most cases, behaved as the Control in nutrients' leaching for all the saturated and unsaturated experiments, both with NPK and FW. Biochar increased EC, K+, and pH of the leaching water, which could be an issue for the growth of some plants. Compost increased NO3− leaching in all the experiments. Zeolites showed the best N compounds retention, but great PO43− leaching in saturated conditions. Heavy metals leachates were analysed only for unsaturated columns (as more representative of field conditions) and found at concentrations well below the limits suggested by the U.S. Environmental Protection Agency. Overall, Graphene performed well in minimizing nutrients and heavy metals leaching, respect to classical improvers. This study is a starting point for field studies that will be critical to have a clear understanding of how Graphene behaves in the environment.

Wheat Crop Yield and Changes in Soil Biological and Heavy Metals Status in a Sandy Soil Amended with Biochar and Irrigated with Drainage Water

The current research aims to study the impacts of adding corncob biochar to a sandy soil irrigated with drainage water on wheat productivity, heavy metals fate, and some soil properties that reflect healthy soil conditions. This research consists of two separate experiments under field (lysimeters) and pot incubation conditions conducted on sandy soil irrigated with drainage water and treated with corncob biochar at the rate of 0.0, 1, 2, and 3% as mixing or mulching. Results specified that drainage water electrical conductivity value (5.89 dS m−1) lies under the degree of restriction on use of “Severe”, indicating that nonstop irrigation with such drainage water may cause a severe salinity problem in soil in the long run. A comparison of heavy metal concentrations of biochar-treated soils with the control showed that total heavy metals had accumulated significantly in the topsoil layer. Most of the available heavy metal concentrations in all soil leachate fractions were below the method detection limits. Mean concentrations of Ni, Cd, and Pb in wheat crops were far below the concentrations considered phytotoxic to wheat plants. More than 90% of the Ni, Cd, and Pb contained in the drainage water of the Al-Moheet drain were significantly present (p ≤ 0.05) and adsorbed by biochar in the top 20 cm of soil lysimeters, indicating the high biochar adsorptive capacity of heavy metals. Total counts of bacteria and fungi gradually and significantly increased over the soil incubation time despite irrigation with contaminated drainage water. Soil resistance index (SRI) values for microbial biomass were positive throughout the experiment and increased significantly as the application rate of corncob biochar increased. These results indicated the high feasibility of using corncob biochar at a rate of 3% to temporarily improve the health of sandy soil despite irrigation with drainage water.

Oxyanion Surface Complexes Control the Kinetics and Pathway of Ferrihydrite Transformation to Goethite and Hematite.

The rate and pathway of ferrihydrite (Fh) transformation at oxic conditions to more stable products is controlled largely by temperature, pH, and the presence of other ions in the system such as nitrate (NO3-), sulfate (SO42-), and arsenate (AsO43-). Although the mechanism of Fh transformation and oxyanion complexation have been separately studied, the effect of surface complex type and strength on the rate and pathway remains only partly understood. We have developed a kinetic model that describes the effects of surface complex type and strength on Fh transformation to goethite (Gt) and hematite (Hm). Two sets of oxyanion-adsorbed Fh samples were prepared, nonbuffered and buffered, aged at 70 ± 1.5 °C, and then characterized using synchrotron X-ray scattering methods and wet chemical analysis. Kinetic modeling showed a significant decrease in the rate of Fh transformation for oxyanion surface complexes dominated by strong inner-sphere (SO42- and AsO43-) versus weak outer-sphere (NO3-) bonding and the control. The results also showed that the Fh transformation pathway is influenced by the type of surface complex such that with increasing strength of bonding, a smaller fraction of Gt forms compared with Hm. These findings are important for understanding and predicting the role of Fh in controlling the transport and fate of metal and metalloid oxyanions in natural and applied systems.

Relevance of sludge management practices and substance modeling in LCA for decision-making: A case study in Chile

Reducing the costs and environmental impacts of sludge management is currently one of the main challenges faced by the wastewater treatment sector. Anaerobic digestion followed by land application has been widely endorsed as a low-impact approach to sludge management, mainly due to the recovery of biogas and the valorization of digestate. However, the influence that the operational conditions of digestion and the management practices of land application can have over the environmental performance of this strategy has been scarcely studied. Furthermore, most of the previous studies dealing with the environmental assessment of this strategy use simplified methods for estimating emissions after land application of sludge, and the lack of systematic accounting of these environmental flows might significantly affect the validity and comparability of the results. Therefore, this work performed an assessment of the influence that 4 relevant practices can have over the environmental impacts of this approach in the context of south-central Chile, providing a mass-balanced inventory for nitrogen, phosphorus and heavy metals in soil based on the ad hoc implementation of models developed for agricultural Life Cycle Assessment (LCA). A total of 16 scenarios were defined and 10 impact categories were evaluated, with the results showing that the environmental impacts were greatly influenced by the variables under study. Overall, solids retention time and the inclusion of pre-treatment mainly influenced climate change, fossil resource depletion and terrestrial ecotoxicity potential, while sludge application rate influenced the eutrophication, water ecotoxicity and human toxicity categories. The type of crop in the receiving soil was a significant driver behind the differences observed in the human toxicity category, which showed the highest variation and relevance in the final weighted result. The results clearly highlight the relevance of using context specific data as well as of quantifying the fate of nutrients, metals and heavy metals during LCA of sludge management. Based on the results, some policy and decision-making recommendations are formulated to optimize the environmental performance of sludge digestion and land application.

Relevance of cell subcompartmentalization techniques to predict adverse effects of metals in bivalves and fish

Subcellular fractionation is an interesting technique to study metal cell compartmentalization and helps on evaluating the impact of a contaminant in an organism. It provides a better understanding about the fate and behaviour of metals within cell compartments, being then able to identify if metals experience a detoxification process or, on the contrary, they are trophically available. Having this information about metals and metalloids is crucial in the context of risk assessment, as it provides valuable information about their behaviour throughout the food chain at different trophic levels.Coastal and marine environments are often affected by dangerous spillages. Pollutants tend to accumulate in water, soils and sediments, where they can become readily available to species, such as bivalves and fish. These species are often used as bioindicators as they can provide information about the trophic transfer and/or the accumulation and of different pollutants. After a bibliographic search, the protocols used to study the subcellular fractionation on bivalves and fish exposed to metals have been highlighted. This literature mini review focuses on the different protocols used for studying this issue and the improvements that subcellular fractionation has brought to the topic. Nonetheless, future research needs and perspectives are pointed out as they can improve the robustness of using such techniques for risk assessment.

Microplastics addition reduced the toxicity and uptake of cadmium to Brassica chinensis L.

The coexistence of microplastics (MPs) and toxic metal contaminants in soils is becoming increasingly common, thereby posing serious threat to soil–plant systems. Cadmium (Cd) is the most common metal contaminant in soil and can easily combine with MPs, thereby altering its bioavailability. However, few studies have focused on the co-pollution of MPs and Cd, particularly the complex phytotoxicity caused by their interaction and the effect of co-exposure on Cd uptake in plants. We conducted pot experiments to compare the effects of exposure to polystyrene (PS) and Cd, as well as the effects of co-exposure (PS + Cd), on the physiological characteristics of Brassica chinensis L. and explored the regulatory factors of MPs on Cd uptake in plant tissues. The results showed that plant biomass, photosynthetic parameters, and chlorophyll content significantly decreased (p < 0.05) with increasing PS doses under treatment with MPs alone. Although the negative effects of PS and Cd co-exposure on plants were higher than those of PS alone, however, the addition of MPs reduced the toxicity effects of Cd on plants and decreased the uptake and accumulation of Cd by plants compared with the Cd treatment alone. Furthermore, plants can resist the increased malondialdehyde content and oxidative stress induced by PS and Cd exposure by increasing the activities of superoxide dismutase and peroxidase. Under the PS + Cd treatment, linear models showed that soil organic carbon and sucrase activity were the key variables affecting Cd uptake by plant shoots and roots, respectively. The results of the partial least squares path modeling further showed that PS indirectly affected Cd uptake by B. chinensis by significantly affecting the physicochemical properties of soil, Cd concentration, and enzyme activity. Our results provide a new perspective and an important reference for further understanding the effects of MPs on the bioavailability and fate of heavy metals.

A state‐of‐the‐art review of the fate of heavy metals and product properties from pyrolysis of heavy‐metal(loid)‐enriched biomass harvested from phytoextraction

AbstractVegetation has successfully been used for cleaning up metal(loid) polluted water bodies and lands through extracting and accumulating of contaminants in their aboveground biomass (phytoextraction). As this remediation technique is approaching extensive demonstration scale application and potential commercialisation, research efforts have been investigating new ways to achieve valorization of its by‐products, the heavy‐metal‐enriched biomass (HMEB). Biomass pyrolysis as an energy conversion technique represents a key step to numerous valorization options of HMEB. During the pyrolysis of HMEB, understanding the thermal decomposition pathways, and the migration and transformation of metal(loid)s are critical for the production of clean, safe and value‐added end‐products. This work performs a state‐of‐the‐art review of the studies conducted on phytoextraction and biomass pyrolysis of HMEB with emphasis on the properties of pyrolysis products as well as the behavior of heavy metal(loid)s during pyrolysis in relation to HMEB feedstock properties and the variables of the process.

Sources, transfers and the fate of heavy metals in soil-wheat systems: The case of lead (Pb)/zinc (Zn) smelting region

Heavy metals (HMs) from smelters pose severe challenges to the environmental soil quality of surrounding farmlands, and threaten human health through the food chain. This study explored the environmental effects of smelting activities on farmland soil, and additionally assessed the enrichment, transfer and health risk of HMs in soil-wheat systems. Multiple characterization results were combined to demonstrate that HMs from smelter waste were transferred to the surrounding soil. It was determined that the enrichment of HMs in soil-wheat systems is mainly controlled by the total HM concentration and pH in soil. Furthermore, the priority pollutant in soil-wheat systems was found to be Cd, and Cd affected the transfer of Cu, Mn and Pb from soil to wheat roots. Interestingly, the -OH stretching, C-H stretching, N-H amide and C-O bending were involved in detoxifying HMs in wheat. The mean values of non-carcinogenic and carcinogenic risks by consuming wheat grain were 9.1, 1.4E-02 (adults) and 11.3, 3.3E-03 (children), respectively, indicating a noteworthy health risk. This study highlighted the critical issues arising from Pb/Zn smelting activities on agricultural soils. Notwithstanding, to ensure food security, the affected regions could opt to follow up on the type of crops grown.

Fate and health risk assessment of heavy metals in Brassica chinensis L. (pak-choi) and soil amended by sludge-based biochar.

Biochar is widely used in agriculture to efficiently solve the problem of sludge. In this study, sludge-based biochar (referred to as BC1, BC2, and BC3) was prepared by mixing sludge with FeCl3, Na2SiO3, and Ca (H2PO4)2, respectively. Then, it was mixed with fresh soil to plant Brassica chinensis L. The analysis of the effects of the three biochar types showed that all of them were beneficial to the growth of Brassica chinensis L. We added the biochar to the soil and found that the concentration of heavy metals did not exceed the recommended threshold. Additionally, the aboveground part of Brassica chinensis L. met the standard requirement for food safety (GB 2761-2017). Notably, BC3 stood out with the best effect on the growth of Brassica chinensis L. and resulted in the improvement of the physical and chemical properties of soil such as ammonium nitrogen, available phosphorus, and available potassium (BC3 was followed by BC2 and BC1). BC3 could efficiently inhibit the migration of heavy metals, thereby reducing the overall heavy metal pollution level and ameliorating the soil nutrients. BC3 could increase the organic carbon by 258.92%, available phosphorus by 234.45%, and available potassium by 37.12% compared with the CK group. The THQ and TTHQ estimates of Brassica chinensis L. were lower than one, indicating that the health risk of heavy metal intake was not prominent. Additionally, the application of the proposed biochar could reduce the form of F1 (acid extracted state) and increase the form of F4 (residue state) in soil. Overall, we conclude that the application of the proposed biochar can promote the root absorption of heavy metals and inhibit the migration of heavy metals.

Hydrothermal carbonization of digested sewage sludge: The fate of heavy metals, PAHs, PCBs, dioxins and pesticides

Hydrothermal carbonization (HTC) is emerging as a promising technology for the management of sewage sludge. The fate of phytosanitary products, Polycyclic aromatic hydrocarbons (PAHs) and PCBs (Polychlorinated biphenyls) after HTC, as well as the formation of dioxins and furans, is still unclear. Moreover, only little information is available on the distribution of heavy metals and major nutrients between the hydrochars and the process water. Here, we aim to contribute to fill these gaps. HTC of sewage sludge from six different wastewater treatment plants has been carried out at 220 °C for 85 min. Feedstock, hydrochars and spent liquor have been then characterized and discussed.HTC is here proven to be a suitable technology for the immobilization of both heavy hydrocarbons and heavy metals, with the exception arsenic, which was also found in the spent liquor at a significant proportion (∼15–∼50%). DDD, DDT, DDE were detected in all sludge samples and their content was reduced by nearly one order of magnitude after the process. HTC is here proven to not be responsible at an appreciable extent of PCBs enrichment of the processed solids. Moreover, the sum of PCDDs and PCDFs in hydrochars never exceeded 20 ng kg−1 s.s.The results obtained encourage further developing of HTC, with the aim to improve the sustainability of sewage sludge management. Additional studies on the environmental impact of hydrochar when used as alternative fuel, as well as soil amendment, could lead to the overcoming of the issues which still hinder these applications.

Tracking cellular transformation of As(III) in HepG2 cells by single-cell focusing/capillary electrophoresis coupled to ICP-MS

The cellular metabolism of metals is highly critical to elucidate their potential cytotoxicity or cell protection mechanism. In this work, an asymmetric serpentine microfluidic device (ASMD) with high sampling efficiency and excellent focusing performance was developed for single-cell focusing. ASMD coupling with ICP-MS ensures single-cell assay to provide the information for trivalent arsenic (As(III)) uptake by HepG2 cells, which reveals the heterogeneity of cellular arsenic distribution, and elucidates the arsenic elimination behaviors in single HepG2 cells. Further, the metabolism and transformation of As(III) in HepG2 cells was tracked by hyphenating capillary electrophoresis (CE) separation with ICP-MS. The results for single-cell analysis and arsenic elimination kinetics illustrated that the half-life of arsenic elimination is 0.9 ± 0.04 h with the elimination constant of 0.77 ± 0.03, i.e., 77% of accumulated As in HepG2 cells may be eliminated per hour. Moreover, arsenobetaine (AsB) was identified to be the main metabolite and biotransformation species of As in HepG2 cells. ASMD-ICP-MS and CE-ICP-MS are powerful for tracking the fate of metals or metal drugs in single cells to comprehensively understand their metabolic pathway and transformation behaviors.

Formation of crystalline multimetallic layered double hydroxide precipitates during uptake of Co, Ni, and Zn onto γ-alumina: Evidence from EXAFS, XRD, and TEM

While the phenomenon of surface adsorption of heavy metals occurring at the mineral-water interface is well understood, the mechanisms of surface precipitation in controlling the fate of heavy metals in soils and water have not been clearly addressed. In this research, we used a combination of extended X-ray absorption fine structure (EXAFS) spectroscopy, high-resolution transmission electron microscopy (HRTEM), and X-ray diffraction (XRD) to determine the uptake mechanisms of Co, Ni, and Zn on γ-Al2O3 at pH 7.5. EXAFS analysis revealed the formation of multimetallic layered double hydroxides (LDHs), and the Me–Me distances (Me = Co, Ni, and Zn) of the multimetallic LDH were inversely correlated with the molar ratio of the sorbed Ni and the sorbed total metals. The HRTEM analysis showed that flake or needle-like shapes of the LDH precipitate formed at the nanoscale. Additionally, XRD suggested that these multimetallic LDHs were crystalline, and the crystallinity was dependent on the heavy metal type. This provides, for the first time, experimental evidence for the formation of CoNiZn–Al LDH precipitates at mineral-water interfaces. These results have pronounced environmental implications in heavy metal remediation, reactive transport modeling, and environmental risk assessment.

Sulfide modifies physicochemical properties and mercury adsorption of microplastics

Microplastics (MPs) tend to accumulate and undergo a sulfur weathering process that leads to significant surface changes in sulfur-rich anaerobic environments, such as sewage and wastewater treatment plants. Aged MPs can have a profound impact on environmental behaviors of various toxic pollutants, especially heavy metals. Although previous studies have investigated the adsorption characteristics of metal ions on MPs that are aged in aerobic environments, the sorptive interactions of sulfur-aged MPs in anaerobic environments with mercury, i.e., Hg(II), are largely unknown. In this study, laboratory investigations were conducted to study the sorptive behaviors of Hg(II) by six common MPs treated anaerobically in the presence of sulfide. Adsorption isotherms show that the sulfur aging process greatly enhances the MP sorption capacity of Hg(II). The mechanisms including changes in the specific surface area, electrostatic interactions, surface precipitation, and surface functional groups are responsible for the enhanced adsorption capacities of sulfur-aged MPs. The thiol group that forms on the MP surface plays a dominant role in enhancing the MP adsorption capacity of Hg(II), which is determined by the formation of unsaturated bonds in the molecular chains of MPs. Furthermore, the pathways of surface chemical transformation of MPs during sulfur aging have been proposed. This study promotes our understanding of the potential hazard of MPs as well as the fate and transport of heavy metals in the presence of aged MPs.