Speciation Of Heavy Metals Research Articles

Spatial distribution, ecotoxicity and human health assessment of nutrients and heavy metals in river sediment under urbanization – A study case of Yitong River, China

ABSTRACT We investigated the contents and distributions of nutrients and heavy metals in sediment from the Yitong River. The main aims were to analyze heavy metals speciation and evaluate their bioavailability, in order to assess the risks they pose to both ecosystem and human health. The average total nitrogen (TN), total phosphorus (TP), organic matter (OM) and Cd, Cr, Cu, Ni, Pb and Zn contents were 1747.69, 895.58, 75103, 0.19, 75.64, 33.61, 47.17, 56.65 and 159.91 mg kg−1, respectively. Results from acid-extraction fraction analysis showed that the proportions of Cd and Zn ranged from 3.78% to 30.20% and 5.31% to 30.74%, respectively. Health risk assessment model showed the risk index values of children and adults were 0.412 and 0.059, respectively, indicating a minimal threat to human health. Multivariate statistical analyses revealed that TN and TP may have similar sources and could be attributed to combined sewer overflows, while Cr, Cu, Ni and Zn were primarily derived from industrial pollution sources. Toxicity bioassay tests demonstrated that the majority of sediment samples were classified as non-toxic. However, 25% of the samples showed slight toxicity towards Vibrio qinghaiensis Q67, while 7% of the samples exhibited slight toxicity towards Daphnia magna. Based on these findings, it is necessary to implement pollution control measures and conduct assessments of aquatic ecological risks in sediments from urban rivers. These results can be used to develop effective strategies for the management and governance of aquatic sediments.

Heavy metals analysis of S. schall and O. niloticus fish species sold at Otuocha Market, Anambra State, Nigeria

The potentials of heavy metal pollution in natural environments have necessitated the need to determine the presence of heavy metal pollutants in the surface waters and possible bioaccumulation in the inhabiting fish species and other aquatic organisms. This study thus aimed to determine the heavy metal species that occur outside their recommended ranges in the test fish species and two Cichlid fish species namely, Synodontis schall and Oreochromis niloticus were selected for the analysis. Water samples were taken to assess the concentrations of these heavy metals in the river while tissues and organs of the test fish samples were extracted for further analysis to determine the cumulative tendencies of these metals in the organisms. All the heavy metals (Cd, Zn, Mn, Cu, Pb) were detected in the fish organs except copper (Cu) which was not detected in the fillet/tissue. The metals occurred in the order; Pb > Zn > Cd > Cu > Mn in both fish species. The gill emerged as the organ with the highest concentration of heavy metal with a value of 100.92ppm of lead in Synodontis schall and 111.34 ppm in Oreochromis niloticus. The high concentrations of Zinc and Lead found in the fish organs were compared with the habitat and discovered that the concentrations were high compared to the lower levels found in the river water. Although Zn occurred at very high concentrations, they were still below the threshold recommended by WHO/FAO. However, Cadmium and Lead exceeded their permissible limits, Lead occurred in outrageous amounts while other metals tested (Mn, Zn, Cu) fell within acceptable ranges. Nonetheless, care should be taken and environmental laws and policies guiding the use and discharge of harmful substances put in place to check the influx and accumulation of these toxicants which pose as threat to man. Metal pollution results in abnormal physiological function of the body cells when they exceed these limits and so guidelines on the use of related products and industrial discharge of effluents should be adhered to and penalty measures taken out on defaulters.

Calcination of sewage sludge-based sulphoaluminate cement clinker: Mineral formation mechanism and heavy metal transition behaviors

Utilizing sewage sludge (SS) to calcinate sulphoaluminate cement (SAC) is a promising technology for low-carbon transition of cement industry, but the unclear effects of SS-contained heavy metals limit the application of this technology. In this study, the effects of SS addition on the calcination of SAC clinker and the transformation of heavy metals were studied from the aspects of mineral phase change, microstructure evolution and heavy metal speciation respectively, covering the mineral formation temperature 900–1250 °C. The results show that the added SS will reduce the formation temperature and change the reaction pathways of mineral phases. When the content of SS increases from 10% to 25%, the compositions of mesophases CaO·Al2O3 and 4CaO·2SiO2·CaSO4 increase by 6.33% and 9.73%, respectively. Meanwhile, the formation of minerals will solidify Zn, Ni, Mn, Cu, Cr, and convert them into a more stable fraction (residual fraction), indicating a lower probability to harm the environment. Moreover, heavy metals present different migration behaviors. After calcination, Mn migrates from SS to 4CaO·Al2O3·Fe2O3 (52.48%), while Zn prefers to enter 3CaO·3Al2O3·CaSO4 (43.74%) and 4CaO·Al2O3·Fe2O3 (38.06%). This study offers new insights into the mineral formation mechanism and heavy metal transition behaviors of sewage sludge-based SAC.

Polyethylene degradation and heavy metals leaching under realistic tropical marine climate

The study examines the influence of temperature and pH on the leaching of six heavy metals (HMs) species: aluminum (Al), zinc (Zn), chromium (Cr), copper (Cu), lead (Pb) and arsenic (As) from transparent polyethylene pellets into seawater. The idea is to understand the potential influence of intensifying global warming and ocean acidification towards microplastic toxicity in the ocean. HMs leaching was obvious by 24th hours, with most HMs concentration decreased in water by 120th and 240th hours except Al. Nevertheless, we report that temperature and pH do not influence the overall HMs leaching from PE pellets with statistical analysis showing no significance (p < 0.05) between temperature and pH toward HMs concentration. Instead, it is hypothesized that these two parameters may be crucial in promoting heavy metal adsorption onto PE pellets under tropical weathering. However, Field Emission Scanning Electron Microscope (FESEM) revealed that temperature and pH are influential in polymer aging and surficial breakdown where pellets exposed in warm, acidic waters showed the greatest extent of weathering. This study highlights that PE pellets exposed under tropical conditions may accelerate surficial degradation and possibly stimulate HMs adherence to the polymer as a pollution vector. Further consideration of metal behaviour in water and microbial activities is crucial to improve our understanding of microplastic toxicity under tropical weathering.

Biochar Derived from Post-Adsorbent for Immobilizing Cu and Cd in Sediment: The Effect on Heavy Metal Species and the Microbial Community Composition.

Many biomass wastes or their modified forms have been investigated as heavy metal adsorbents. However, less emphasis has been placed on post-adsorbent management or possible further utilization. In this study, biochar (BC) derived from modified bamboo adsorbent after the adsorption of Cu from an aqueous solution was used for the in situ remediation of lake sediment contaminated with Cd and Cu. The results indicated that the Cu concentration was extremely low (≤0.015 mg/L), while Cd was not detected in the overlying water or the interstitial water after the 90-day BC treatment. The pH value (7.5-8.1) slightly increased, and the toxicity characteristic leaching procedure (TCLP) leachability of the Cu and Cd in the sediment decreased overall. Cu and Cd were preferentially transformed into more stable species. The findings highlighted the potential possibility of BC derived from post-adsorbent being used for sediment remediation. However, the BC addition produced significant effects on the sediment microbial activity and community structure. In general, with an increase in BC, the urease activity increased, while the alkaline phosphatase and invertase activity decreased, which could be attributed to the BC itself. In addition, significant changes in both bacterial and fungal genera were observed. Hence, a cautious approach should be taken in the practical application of BC.

Biosorption of Fe (II) and Pb (II) on unmodified Senna tora: Isotherm and kinetic modeling

Contamination of environment by heavy metals has become a major concern worldwide. The role of conventional methods in remediating heavy metals has become ineffective and costly. Therefore, it becomes imperative to explore bioremediation using a cost effective, efficient and environmentally friendly alternative method of removing heavy metals. In this study, the adsorption behaviour of Senna tora, a low-cost adsorbents, with respect to Fe(II) and Pb(II) ions, has been studied in order to consider its application to the treatment of wastewater. The physicochemical properties of the unmodified Senna tora were predetermined. The batch experimental method was employed: parameters such as pH, contact time, dosage and initial metal concentration were studied. The influence of the pH of the metal ion solutions on the uptake levels of the metal ions by the adsorbent used was carried out between pH 4 and 10. The optimum pH for both Fe (II) and Pb(II) removals by Senna tora was 7. An equilibrium contact time of 60 min was required for the adsorption of Pb(II) ions onto Senna tora. Percentage sorption of Fe(II) increased from 94 to 99% and that of Pb (II) from 94.4 to 96% as adsorbent dose was increased from 2 to 10 g. The isotherms data provide information on the capacity of the adsorbent or the amount required to remove a unit mass of pollutant under the operating conditions. The equilibrium data of Fe(II) and Pb(II) adsorbed onto Senna tora pods were fitted by the Langmuir, Freundlich, and Temkin isotherms. On the basis of correlation coefficients R2, it is concluded that the Fe(II) and Pb(II) biosorption is better fitted to the Freundlich model. This suggests that the biosorption of Fe(II) and Pb(II) on the surface of Senna tora pods occurs on heterogeneous binding sites with equivalent adsorption energies and multilayer coverage. The results demonstrated that Senna tora pod holds potential to remove cationic heavy metal species from industrial wastewater.

Emission Characteristics, Speciation, and Potential Environmental Risks of Heavy Metals from Coal-Fired Boilers: A Review

Coal-fired boilers, including coal-fired power plants (CFPPs) and coal-fired industrial boilers (CFIBs), are an important area for achieving sustainability globally as they are one of the globally important sources of anthropogenic emissions of heavy metals (HMs) due to huge amount of coal consumption. To date, the investigation of atmospheric emission characteristics, speciation, and potential environmental risks of HMs from coal-fired boilers has received widespread attention and achieved significant progress. To characterise the emissions of HMs from coal-fired boilers, research is currently being carried out in the areas of (1) studying the release of HMs from coal combustion processes, (2) developing emission factors and emission inventories, and (3) revealing the cross-media partitioning of HMs between different output streams. Research on the chemical forms of HMs in waste from coal-fired boiler is currently focused on chemical valence and speciation components. The sequential chemical extraction method is currently the most widely used method for investigating the chemical fractionations of HMs in wastes from coal-fired boilers. Studies indicate that different HM elements display differentiated characteristics of speciation in waste from coal-fired boilers. Early studies on potential environmental risk and ecological risk caused by HMs are usually based on actual monitoring values of HMs in the target environmental media. The risk assessment code method and the leaching toxicity method are the most widely used method to study the potential environmental risk of HMs in waste from coal-fired boilers. With the implementation of global carbon emission reduction strategies, the scale of coal-fired boilers and air pollution control technologies are bound to change in the future. Therefore, as an important component of global efforts to achieve sustainable development, more research is needed in the future to improve the accuracy of emission inventories, reveal the mechanisms of HM chemical transformation, and establish methods for potential environmental risk assessment at regional scales.

Improved Calculations of Heavy Metal Toxicity Coefficients for Evaluating Potential Ecological Risk in Sediments Based on Seven Major Chinese Water Systems.

Several methods have been used to assess heavy metal contamination in sediments. However, an assessment that considers both composite heavy metal speciation and concentration is necessary to accurately study ecological risks. This study improved the potential ecological risk index method and calculated the toxicity coefficients of seven heavy metals: Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Nickel (Ni), Lead (Pb), and Zinc (Zn). The newly calculated toxicity coefficients were validated by using previously published heavy metal distribution data of the Henan section of the Yellow River. The calculation procedure is based on the principle that the abundance of heavy metals in the environment and their bioavailable forms affect the toxicity of heavy metals. The toxicity coefficients for the seven heavy metals were calculated as follows: As = 10, Cd = 20, Cr = 5, Cu = 2, Ni = 5, Pb = 5, Zn = 1. Ecological risk assessment of the Henan section of the Yellow River using the improved toxicity coefficients revealed that the ecological risk of Cd and total heavy metals is higher than previous calculations, reaching the strength and moderate risk levels, respectively. The improved potential ecological risk index method is more sensitive to heavy metal pollution and thus provides a better indication of ecological risk. This is a necessary improvement to provide more accurate pollution assessments.

Mineral-organic interactions drive the aging and stabilization of exogenous Pb in soils

The interactions of soil components have profound impacts on the speciation, bioavailability and transformation of heavy metals. However, these interactions have not been well included in multi-surface model (MSM) as most of the models adopt component additive method. Here, an incubation experiment was conducted with three contrasting soils spiked with 200 mg/kg Pb and rice straw to investigate the impact of mineral-organic interactions on Pb speciation and to validate the MSM for Pb in soils. With the aid of chemical extraction and instrumental analysis (XANES and SEM-EDS), the results show that metal oxides and soil organic matter are the main scavengers for Pb, accounting for the stabilization of exogenous Pb by ∼ 40% − 80% and ∼ 13% − 30%, respectively. The accumulation of the most stable residual Pb was driven by Fe/Al oxides, which was fostered by organic matter through the formation of amorphous Fe/Al oxides. Unexpectedly, the introduction of straw promoted the activation of metal oxides and the competition from Fe/Al/Ca ions reduced the binding of Pb by soil organic matter. Simulation of organic-Fe/Al/Ca interactions largely improved the accuracy of the MSM model results for the prediction of Pb speciation distribution. Overall, this study highlights that mineral-organic interactions play important role in the stabilization of exogenous Pb in soils, while incorporate of these interactions into MSM is recommended in future heavy metal studies.

Spatio-temporal variation and hazard assessment of potentially toxic metal element contamination in sediments and water before and after a water-level fluctuation cycle in the Three Gorges Reservoir, Wanzhou, China.

Previous investigations on heavy metals in the water-sediment compartment focused on their spatial distribution, and the influence of sediment pH and organic matter (OM) on metal environmental occurrences. However, there are limited studies on the effects of physicochemical properties on the migration and transformation of heavy metals in the water-sediment compartments. This study investigated the relationship between the physicochemical properties of sediments and the distribution and chemical speciation of heavy metals, and the potential environmental risk of heavy metals in water and sediment using Risk Assessment Code (RAC) values and the Tessier five-step extraction method. Adsorption and desorption experiments showed that the sediment had weak adsorption and the strongest desorption capacity for Cd. Results of the pH, OM, surface element content, and X-ray diffraction (XRD) patterns suggested that cadmium (Cd) was more likely to partition into the water phase from the sediment during the flooding and water storage periods. When pH was 7-8 and OM content was 3.6-5.9%, the sediment-water distribution coefficient of Cd was low due to its large ionic radius, and the surface adsorption sites were saturated by other elements. These studies can provide a theoretical basis for the management and pollution control of the Three Gorges Reservoir.

Effect of Grain Size Distribution of Soil on Immobilization of Cadmium and Nickel in Contaminated Soil Using Nano Zerovalent Iron: A Factorial Design and Response Surface Methodology Approach

Urban soils get contaminated due to the unscientific disposal of industrial effluents and solid waste, contaminating the soil with heavy metals. Contaminated soils need to be remediated to avoid the ingestion of toxic heavy metals. The immobilization of heavy metals is one of the methods to remediate contaminated soils. The primary purpose of this study was to explore the effect of grain size distribution (GSD) of soil on the efficiency of immobilization of toxic heavy metals in soil when nano zerovalent iron (nZVI) is used to immobilize the metals. Preliminary studies conducted with the 23 factorial design method confirmed that GSD is a significant factor along with the level of contamination and nZVI dosage in the immobilization of heavy metals in soil. Experiments were conducted with cadmium (Cd) and nickel (Ni), the toxic heavy metals, and three soils with different finer particles than 75 µm. Immobilization efficiency was obtained by comparing the leachability of contaminated and treated soil samples using the toxicity characteristic leaching procedure. Reduction in available fraction and variation in the speciation of heavy metals was observed through the sequential extraction procedure. The response surface methodology was adopted for analysis with three levels of GSD, contamination, and nZVI dosage. For Cd, a reduced cubic model was the best fit with a coefficient of determination (R-square) of 0.93, and for Ni, a quadratic model was the best fit with an R-square of 0.92. Both these models were validated experimentally. The efficiency variation followed an optimum curve concerning GSD, contamination level, and the nZVI dosage. For multimetal contamination, the immobilization efficiency gradually decreased from 10% finer to 90% finer soil, both in the case of Cd and Ni. It was observed that for both single metal and multimetal contamination, the interaction between soil and the nZVI plays a vital role in immobilization along with the factors considered.

Exploring The Potential of Mango Seed as A Bioadsorbent for Pb(II) Removal in Aqueous Solution

Various industrial activities produce heavy metals as by-products or wastes. Lead is a metal trace element from sewage disposal, vehicle fumes, and atmospheric emissions from industrial activities. Mango seeds are composed of cellulose, lignin, and hemicellulose, which have many potential binding groups. Mango seeds, which are often considered waste, can be utilized as a low-cost biosorbent due to their various functional groups, such as hydroxyl, carboxyl, carbonyl, alcohol, amide, and aromatic groups. Mango seed are organic waste with potential as low-cost biosorbent for heavy metals removal. The purposes of the study are: (1) to explore the optimum condition of biosorbent in absorbing heavy metal species (Pb (II)), and (2) to analyze the adsorption model of synthetic waste containing Pb(II). Mango seeds have a considerable potential to be used as a biosorbent to absorb heavy metal ions. The optimum conditions for Pb2+ ion adsorption is at pH 6 with contact time 70 minutes, and concentration of biosorbent 2.0 g/L. Adsorbate adsorption follows the Freundlich model, and adsorption occurs only in a few surface layers. The kinetic parameters of adsorbent satisfied pseudo-second-order reaction. The optimum adsorption capacity (qm) of mango seed biosorbent in absorbing Pb ions is 43.86 mg/g.

Research advancements in nutrients and heavy metals, its speciation and behavior during hydrothermal carbonization of sludge – A critical review

Due to rapid increase in urbanization generation rate of sludge is expected to reach over 60 million tonnes hence its proper management has become necessary more than ever. Although, sludge is a complex mixture substance having high moisture content, low energy density and possesses several pollutants but it is also a carbon rich material having potential of resource utilization which attracts many thermochemical techniques to convert it into high value product. Hydrothermal carbonization (HTC) is an efficient pre-treatment technique of converting moisture waste material to high value product with low energy consumption. Phosphorus and nitrogen are major nutrients for agriculture and due to HTC, they can be recovered from hydrochar (HC) as well as process water depending on various conditions. Secondly, the presence of heavy metals is limiting the applicability of sludge-derived HC as soil conditioner and they can be easily transferred to human beings via crops. High ash content in sludge-derived HC is disadvantageous for using it as a fuel. Therefore, this review paper critically discusses transforming mechanism and speciation of nutrients and heavy metals (HMs) for fully utilization of sludge through HTC and how additives (oxides, acids and inorganics) are affecting behavior of nutrients and HMs is systematically discussed. In the end, future perspectives have been discussed for its efficient utilization.

Investigation of the redox behavior of biochar-based bipolar electrochemistry in porous media

Bipolar electrochemistry (BEC) refers to the redox actuation occurring at the wirelessly connected conductors, the bipolar electrodes (BPEs), but the redox behavior of biochar-based BEC in porous media remains unclear. This study evaluated the redox behavior of biochar-based BEC in porous media using the conversion rates of Cr(III) and Cr(VI). Results showed activated BEC in porous media, with bamboo biochar (B-BC) BPEs exhibiting superior redox properties compared to wood (WO-BC) and walnut biochar (W-BC). Soil texture influenced BEC performance, with sandy soils exhibiting the highest Cr conversion rates (36.22% for Cr(III) to Cr(VI) and 48.6% for Cr(VI) to Cr(III)). A linear relationship existed between Cr conversion and voltage gradient (2.2–4.2 V/cm). Excessive biochar addition (>2.5% w/w) reduced Cr conversion. Further analysis revealed exceptional electron transfer capability of B-BC and WO-BC, producing ·O2- and ·OH with catalytic activation and indirect oxidation potential. Overall, our findings suggest biochar-based BEC induction in porous media, facilitating rapid changes in heavy metal speciation, primarily driven by direct oxidation of biochar. Exceptional biochar behavior arises from intricate properties such as honeycomb structures, quinoid groups, phenolic-OH, and high crystallinity. Optimizing biochar's structure, functional groups, and crystallinity holds promise for effective implementation of biochar-based BEC in porous soil remediation.

Comparison of urban and rural soils based on speciation of heavy metals by BCR sequential extraction procedure: A case study in the historical and industrial city of Sisak, Croatia

Within the framework of the pan-European project “URban GEochemistry (URGE) in Europe – Soil, children, health”, pedological and geochemical investigations of the soils of the city of Sisak and its adjacent surroundings were carried out, and three urban and two rural soil profiles were examined. The mineralogical composition and concentration of selected potentially toxic elements (PTEs) Cr, Cu, Ni, Pb and Zn in the soil were determined. The Community Reference Bureau of Reference (BCR) sequential extraction procedure (SEP) of these PTEs was undertaken and the potential risk to human health and the environment was assessed. The concentrations of Cr and Ni are generally similar in urban and rural soil profiles, while the concentrations of Cu, Pb and Zn in soil horizons/layers are higher in urban profiles. The extracted fractions of PTEs gave the following general distribution: in urban soil profiles residual (RES) &gt; reducible (ORG) or oxidisable (FEMN) &gt; exchangeable (CARB), except for Cu where ORG &gt; RES &gt; FEMN &gt; CARB, while in rural soil profiles RES &gt; FEMN or ORG &gt; CARB, except for Pb where FEMN &gt; RES or ORG &gt; CARB. The differences between soils in urban and rural profiles depend mainly on the historical land use, i.e. on the duration and intensity of anthropogenic influences on the soil and, to a lesser extent, on the geogenic origin of the parent material and the pedogenic processes. The studied elements in the urban soil profiles are predominantly of anthropogenic origin, indicating a possible influence of the ancient settlements of Segestica and Siscia and of heavy industry in the 20th century. The anthropogenic influences on the rural profiles are low and geogenic influences dominate. Risks to the environment were assessed in the soil profiles based on PTE concentrations in the CARB fraction and the sum of the CARB, ORG and FEMN fractions from BCR SEP. All calculated risks to human health and the environment were rated as no-risk, very low risk and low risk.

Investigation of heavy metal and micro-macro element speciation in biomass ash enriched sewage sludge compost

The objective of this study was to enrich the nutrient content of compost and to investigate the passivation and solubilization of plant micronutrients (Fe, Al, Cu, Ni, Zn, Na, Mn), macroelements (P, K, Mg, Ca), and heavy metals (Cr, Cd, Pb) during sewage sludge composting with nutrient-rich biomass ash additives. T0: 0%, T1: 3.5%, T2: 7.0%, and T3: 14.0% dry weight (DW), weight/weight (w/w) biomass ash was added to the sewage sludge + sawdust mixture (volume, 1:1) to obtain the final NPK content and monitored over a 45-day period. Sawdust was used as auxiliary material. The sequential extraction method was used to determine the elemental species. Cr, Cd and Pb showed higher affinity to the residual fraction and occluded in the oxide fraction, which decreased the bioavailability factor (BF) (<1% BF–Cr, 21% BF–Cd and 9% BF–Pb) compared to the control treatment (46% BF–Cr, 47% BF–Cd and 80% BF–Pb). As the amount of biomass ash increased (T1-T3), the percentages of residual Cr (Res-Cr) (10–65%), exchangeable Cd (Exc-Cd) and organically bound Cd (Org-Cd) (14% and 21%), and oxides-Pb (Oxi-Pb) (20–61%) increased. In all composts, Fe, Al, and Cu were associated with organically bound and oxides-entrapped fractions. More than 50% of total Mn and Mg were concentrated mainly in exchangeable fractions, suggesting high mobility and bioavailability (42% BF–Mn and 98% BF–Mg). Ni, Zn, and Na tended to be present in oxide-bound, organically bound, and residual fractions, while K and P were associated with exchangeable and organically bound fractions. The overall results suggest that composting sewage sludge with biomass ash may be the best strategy and technique to overcome soil application bottlenecks because it passivates heavy metals and improves the bioavailability of plant nutrients.

Chemical Speciation Distribution and Thermal Stability of Heavy Metals along Flue Gas Cleaning Systems in a Hazardous Waste Incinerator

Hazardous heavy metals may release from incineration residues in the utilization concerning heat treatment or landfills, which would cause great harm on the environment. The evaluation of chemical speciation and thermal stability of heavy metals are of great significance for the control of heavy metal pollution during heat treatments. In this study, chemical speciation distribution and thermal stability of heavy metals (As, Cd, Cr, Cu, Pb, Se, Zn, and Hg) along flue gas cleaning systems were investigated in a hazardous waste incinerator located in Zhejiang, China. The chemical speciation and thermal stability of heavy metals, environmental risk evaluation, and morphological and mineralogical characteristics of incineration residues were assessed before and after heat treatments. Results indicated that the chemical speciation of heavy metals in the bottom slag, burn-out chamber ash, boiler ash, and bag filter ash varied significantly. The thermal stability of heavy metals in the incineration residues was significantly influenced by chemical speciation, and the thermal stability of the chemical speciation decreased basically in the order of residual form > reducible form > oxidizable form > acid soluble form. As, Cr, and Se showed high thermal stability due to the fact that they were involved in the crystallization reaction, and heat treatment would promote the transformation from mobile fractions into the residual fraction. Hg and Cd displayed the worst thermal stability, and high-temperature heat treatment would contribute to secondary volatilization from the incineration residues. More attention should be paid to the secondary volatilization of Hg and Cd during thermal disposal. Cu, Pb, and Zn had moderate thermal stability, and heat treatment would cause the volatilization of mobile fractions and the transformation from mobile fractions into the residual fraction. Pretreatments such as water-washing or adding a chemical stabilizer would be conducive to reducing the volatilization of heavy metals during thermal disposal.

Behavior, risk, and bioremediation potential of heavy metals/metalloids in the soil system

The application of pesticides and chemicals in agriculture and industrialization occasioned in meagre soil quality, which has a serious global concern. The most prevalent type of soil pollutants is inorganic contaminants, metals–metalloids, and organic pollutants like herbicides, pesticides, and polycyclic aromatic hydrocarbons. Even though heavy metals are essential for sustaining soil health, a slight increase in their concentration beyond the permissible limit can harm the soil. These metals cannot be degraded entirely but can be changed from highly toxic to less poisonous by chemical or biological methods. Further, the mobility of pollutants in soil-based environments might be increased due to competition among other heavy metal species for their available adsorption on the soil matrix. These heavy metals are hazardous in high concentrations to plants and animals. In addition to hindering nutrient uptake and limiting seed germination, excessive metal exposure also causes shoot growth to slow down, and lipid peroxidation occurs. In the present article, we see how these heavy metals accumulate continually in the soil and are later absorbed by plants. To appraise the impact of contamination and toxicity by the heavy metals in soil, their fate, transport, and toxicity mechanisms in soil systems have been described. The bioremediation strategies such as biosorption, siderophore formation, phytoremediation, phytovolatilization, and phytostabilization have also been discussed to understand the biodegradation of metalloids. Also, microbial remediation and genetic transformation are the biotechnological aspects employed to increase the degradation efficiency of heavy metals.

Seasonal heavy metal speciation in sediment and source tracking via Cu isotopic composition in Huangpu River, Shanghai, China

The present study systematically analyzed and evaluated the variations in chemical speciation, pollution assessment, and source identification of heavy metals in sediments of Huangpu River. The methods employed included heavy metal concentration, chemical speciation and Cu isotopic compositions analysis. Results showed that the chemical speciation of sediment-bound heavy metals, characterized by significant seasonal variation, shifted from non-residual fractions dominating in spring and summer to residual fractions dominating in autumn and winter. Precipitation was identified as an important factor influencing the chemical speciation of sediment-bound heavy metals. Furthermore, ratio of the secondary phase to the primary phase, RSP (=Cnon-residual/Cresidual) values in Huangpu River sediments were higher than 1 in spring and summer, indicating that sediment-bound heavy metals in Huangpu River were mainly composed of non-residual fractions and could potentially be released into the river water. Principal component analysis (PCA) revealed that navigation, traffic, agricultural, and industrial activities could be the potential sources of heavy metal pollution. Notably, the δ65Cu values in Huangpu River sediments were observed to be isotopically lighter (from −0.37 to +0.18 ‰), suggesting that navigation might be the primary pollution source. These results will not only provide guidance in reducing heavy metal concentrations, but also serve as a crucial basis for policy making regarding heavy metal control.

An investigation on mobility of heavy metals for assessing the reusability of soil-like material reclaimed from mining of municipal solid waste dumpsites

Landfill mining, often referred to as “bio-mining”, enables the recovery of resources, including combustible, compostable, and recyclable fractions from landfills. However, most of the materials mined from old landfills mainly consist of soil-like materials (SLM). The reuse of SLM depends on the concentration of contaminants, such as heavy metals, soluble salts, etc. A sound risk assessment requires sequential extraction to determine the bioavailability of heavy metals. This study focuses on the mobility and chemical speciation of heavy metals in SLM from four old municipal solid waste dumpsites in India by performing selective sequential extraction. Additionally, the study compares the results with those of four previous investigations to identify international similarities. It has been observed that Zn was mainly available in the reducible phase (average 41%), whereas Ni and Cr proved to have the highest distribution in the residual phase (64% and 71%, respectively). Pb analysis showed a large portion in the oxidizable phase (39%), while Cu was mainly present in the oxidizable (37%) and residual (39%) phases. Similarities with previous investigations were observed for Zn (primarily reducible 48%), Ni (residual 52%), and Cu (oxidizable 56%). Correlation analysis showed that Ni correlated with all heavy metals (ρ = 0.71–0.78), except with Cu. The present study suggested that Zn and Pb are associated with a high risk of pollution due to their maximum distribution in the bioavailable phase. The findings of the study can be used to assess the heavy metal contamination potential of SLM prior to its reuse in offsite applications.