Environmental Risk Of Heavy Metals Research Articles

Environmental remediation potential of a pioneer plant (Miscanthus sp.) from abandoned mine into biochar: Heavy metal stabilization and environmental application

Pyrolysis stands out as an effective method for the disposal of phytoremediation residues in abandoned mines, yielding a valuable by-product, biochar. However, the environmental application of biochar derived from such residues is limited by the potential environmental risks of heavy metals. Herein, Miscanthus sp. residues from abandoned mines were pyrolyzed into biochars at varied pyrolysis temperatures (300–700 °C) to facilitate the safe reuse of phytoremediation residues. The results showed that pyrolysis significantly stabilizes heavy metals in biomass, with Cd exhibiting the most notable stabilization effect. Acid-soluble/exchangeable and reducible fractions of Cd decreased significantly from 69.91 % to 2.52 %, and oxidizable and residue fractions increased approximately 3.24 times at 700 °C. The environmental risk assessment indicated that biochar pyrolyzed over 500 °C pose lower environmental risk (RI < 30), making them optimal for the safe utilization of phytoremediation residues. Additionally, adsorption experiments suggested that biochars prepared at higher temperature (500–700 °C) exhibit superior adsorption capacity, attributed to alkalinity and precipitation effect. This study highlights that biochars produced by pyrolyzing Miscanthus sp. from abandoned mines above 500 °C hold promise for environmental remediation, offering novel insight into the reutilization of metal-rich biomass.

Potential of artificial soil preparation for vegetation restoration using red mud and phosphogypsum

Red mud and phosphogypsum have long been a focus and challenge in global industrial waste management, and their low-cost and large-scale utilization technology has always been an urgent need. This study is based on the strong acid-base neutralization reaction between red mud and phosphogypsum, which contain an elemental composition similar to that of natural soil, red mud itself has characteristic of clay minerals, and other auxiliary materials (i.e. rice husk powder, bentonite, fly ash, polyacrylamide flocculant and microbial suspension) were added, so as to explore the potential of synergistically prepared artificial soil for vegetation restoration. The results showed that the artificial soils exhibited physicochemical characteristics (e.g., pH, moisture content, cation exchange capacity) similar to those of natural soil, along with abundant organic matter, nitrogen, phosphorus, and potassium contents, meeting the growth requirements of plants. The artificial soils were able to support favorable growth of suitable plants (e.g., sunflower, wheat, rye grass), accumulating high levels of diverse enzymatic activities, comparable to those in natural soils (e.g., catalase, urease, phosphatase), or even surpassing natural soils (e.g., sucrase), and rich microorganism communities, such as Cyanobacteria, Proteobacteria, Actinobacteria in the bacteria domain, and Ascomycota in the fungi domain, were initially developed. It's suggested that preparing 1 ton of artificial soil entails synergistic consumption of 613.7 kg of red mud and 244.6 kg of phosphogypsum, accounting for mass proportions of 61.4 % and 24.5 %, respectively. In future, more evaluations on the leaching loss of nutrients and alkalinity and the environmental risks of heavy metals should be conducted to more references for the artificial soil application. In summary, the preparation of artificial soil is a very simple, efficient, scalable and low-cost collaborative resource utilization scheme of red mud and phosphogypsum, which has great potential for vegetation restoration in some places such as tailings field and soil-deficient depression.

Investigation of the speciation and environmental risk of heavy metals in biochar produced from textile sludge waste by pyrolysis at different temperatures

The aim of the present study was to find environmentally friendly solutions for the disposal of problematic and toxic textile sludge (TS) by producing textile sludge biochar (TSB) by pyrolysis and evaluating its chemical properties, polycyclic aromatic hydrocarbon (PAH) content, heavy metals (HMs) speciation, environmental risks, and effects on seed germination. Pyrolysis of TS at temperatures ranging from 300 to 700 °C significantly reduced (85–95%) or eliminated certain PAHs in the biochar, enriched heavy metal content within land use limits, and increased bioavailability of HMs in biochar produced at 300 °C and decreased leaching capacity of HMs in biochar produced at 700 °C. The speciation of HMs and their bioavailability during pyrolysis processes was strongly temperature dependent, with lower temperatures increasing the toxic and bioavailable forms of Zn and Ni, while higher temperatures converted the bioavailable Ni to a more stable form, while Cu, Cr, and Pb were transformed from stable to toxic and bioavailable forms. The ecological risk index (RI) values of TSB-300 and TSB-700 are below the threshold value of 150, indicating a low-risk level, and the risk level decreases at temperatures above 500 °C. Further, the extracts of TSB-300 and TSB-700 had the highest percentage of germinating seeds, while the extracts of TS and TSB-500 inhibited seed germination by 20–30% compared to the control. These results indicate that pyrolysis effectively reduces PAHs and binds leachable HMs in biochar, however, the specific pyrolysis temperature influences metal speciation, bioavailability, seed germination, and environmental risk.

An environmentally benign process for effective recovery and solidification of Cr from stainless-steel slag

Stainless-steel slag is a hazardous solid that has caused severe chromium contamination globally. This study proposes an environmentally benign vitrification process for efficient recycling and solidification of Cr from stainless-steel slag using waste copper slag and coal tar residue. The transformation behaviors of heavy metals (Cr, Cu, Pb, Zn) and the Cr toxic leaching mechanism are also determined in this work. The findings indicated that compared with Cu and Fe phases, the Mg(Al,Cr)2O4 and chemically dissolved Cr phases were not easily reduced via coal tar residue, leading to the leaching of highly toxic Cr3+/Cr6+ during the toxicity characteristic leaching procedure (TCLP). Under optimal conditions, 95.56% Cr, 97.71% Fe, and 99.71% Cu could be recovered in the form of high value-added crude stainless-steel, and 99.62% Pb and 99.19% Zn could be enriched in the dust. The furnace slag TCLP result indicated that the leaching concentrations of Cr, Cu, Pb and Zn were 1.82 mg/L, 0.1 mg/L, 0.38 mg/L, and 2.58 mg/L, respectively. More importantly, the concentrations of residual Cr, Cu, Pb and Zn in the furnace slag were only 0.095 wt%, 0.028 wt%, 0.0192 wt%, and 0.011 wt%, respectively. These findings indicate that treated slag can be categorized as general solid waste, minimizing the environmental risks of heavy metals. The results of this study are significant for the sustainable development of the stainless-steel industry and copper metallurgy.

An environmentally friendly strategy for reducing the environmental risks of heavy metals adsorbed by kaolinite

Plenty of heavy metals (HMs) that are adsorbed on clay minerals (such as kaolinite), in addition to low molecular-weight organic acids (such as oxalic acid (OA)) with high activities, are widespread in the natural environment. In the present study, the effects of OA on the environmental behaviors of Pb2+/Cd2+ adsorbed by kaolinite have been investigated. The effectiveness and mechanisms of calcium silicate (CS) and magnesium silicate (MS) in reducing the environmental risks of the HMs have also been studied. The results showed that the releases of Pb2+/Cd2+ increased with an increasing concentration of OA. When different dosages of CS/MS were added to the aging system, a redistribution of HMs took place and the free form of Pb2+/Cd2+ decreased to very low levels. Also, the unextractable Pb2+/Cd2+ increased to high levels. Furthermore, a series of characterizations showed that the released HMs were re-captured by the CS/MS. In addition, the CS immobilized the OA in the solution during the aging process, which also facilitated an immobilization of the carbon element in the environment. In general, the present study has contributed to a further understanding of the transport behaviors of the HMs in natural environments, and of the interactions between CS (or MS), the environmental media, and the heavy metal contaminants. In addition, this study has also provided an eco-friendly strategy for an effective remediation of heavy metal pollution.

A study of environmental pollution and risk of heavy metals in the bottom water and sediment of the Chaohu Lake, China.

Most of the existing research for heavy metals in water at present is focusing on surface water. However, potential environmental risk of heavy metals in the bottom water of lakes cannot be ignored. In this study, the content, distribution, and speciation of nine heavy metals (As, V, Cr, Co, Ni, Cu, Zn, Cd, and Pb) in the bottom water and sediment of Chaohu Lake were studied. Some pollution assessment methods were used to evaluate the environmental effect of heavy metals. Positive matrix factorization was conducted to investigate the potential sources of heavy metals in sediment. The contents of heavy metals in the bottom water of Chaohu Lake mean that its environmental pollution can be ignored. In sediment, Cd and Zn have showed stronger ecological risk. pH and redox potential are more likely to affect the stability of heavy metals in the bottom water of Chaohu Lake during the dry reason. Industrial sources (16%) are no longer the largest source of heavy metal pollution; traffic sources (33.6%) and agricultural sources (23.4%) have become the main sources of pollution at present. This study can provide some support and suggestions for the treatment of heavy metals in lakes.

Effectiveness of attapulgite modified by chlorides on speciation and environmental risk of heavy metals in soil

Effectiveness of attapulgite modified by chlorides on speciation and environmental risk of heavy metals in soil

Distribution and Potential Environmental Risks of Heavy Metals in Riverine Sediments of Maa-Dee-Tai River in Sogho Community, Ogoniland, Rivers State, Nigeria

Distribution and Potential Environmental Risks of Heavy Metals in Riverine Sediments of Maa-Dee-Tai River in Sogho Community, Ogoniland, Rivers State, Nigeria

Modulatory Role of Biochar Properties and Environmental Risk of Heavy Metals by Co-Pyrolysis of Fenton Sludge and Biochemical Sludge.

Recent studies have reported that Fenton sludge and biochemical sludge contain high concentrations of toxic substances and heavy metals (HMs), whereas improper treatment can pose serious threats to environmental safety. Pyrolysis is considered an efficient technology to replace conventional sludge treatment. This study investigated the pyrolysis and kinetic processes of Fenton sludge and biochemical sludge, revealed the physicochemical properties of sludge biochar, and highlighted the role of co-pyrolysis in sludge immobilization of HMs and environmental risks. Results showed that Fenton sludge and biochemical sludge underwent three stages of weight loss during individual pyrolysis and co-pyrolysis, especially co-pyrolysis, which increased the rate of sludge pyrolysis and reduced the decomposition temperature. The kinetic reaction indicated that the activation energies of Fenton sludge, biochemical sludge, and mixed sludge were 11.59 kJ/mol, 8.50 kJ/mol, and 7.11 kJ/mol, respectively. Notably, co-pyrolysis reduced the activation energy of reactions and changed the specific surface area and functional group properties of the biochar produced from sludge. Meanwhile, co-pyrolysis effectively immobilized Cu, Pb, and Zn, increased the proportion of metals in oxidizable and residual states, and mitigated the environmental risks of HMs in sludge. This study provided new insights into the co-pyrolysis properties of sludge biochar and the risk assessment of HMs.

Soil moisture dynamics regulates the release rates and lability of copper in contaminated paddy soils

The climate changes have caused more extreme precipitation and drought events in the field and have exacerbated the severity of wet-dry events in soils, which will inevitably lead to severe fluctuations in soil moisture content. Soil moisture content has been recognized to influence the distribution of heavy metals, but how temporal changes of soil moisture dynamics affect the release rates and lability of heavy metals is still poorly understood, which precludes accurate prediction of environmental behavior and environmental risk of heavy metals in the field. In this study, we combined experimental and modeling approaches to quantify copper release rates and labile copper fractions in two paddy soils from southern China under different moisture conditions. Our kinetic data and models showed that the release rates and lability of copper were highly associated with the soil moisture contents, in which, surprisingly, high soil moisture contents effectively reduced the release rates of copper even with little changes in the reactive portions of copper in soils. A suite of comprehensive characterization on soil solid and solution components along the incubation suggested that soil microbes may regulate soil copper lability through forming microbially derived organic matter that sequestered copper and by increasing soil particle aggregation for protecting copper from release. This study highlights the importance of incorporating soil moisture dynamics into future environmental models. The experimental and modeling approaches in this study have provided basis for further developing predictive models applicable to paddy soils with varying soil moisture under the impact of climate change.

Volatilization characteristic and solidification of Pb, Zn, Cd and as during cement kiln co-processing of solid waste

Cement kiln co-processing always became one of the predominate approaches to dispose hazardous solid waste containing heavy metals. The volatilization and morphology of heavy metals should be paid to more concern during the cement production due to the environmental risk of heavy metals. In this study, the volatilization characteristics and the solidification effect of heavy metals (Pb, Zn Cd and As) during cement kiln co-processing were explored by the lab and pilot scale experiments. At same experimental conditions, the volatilization rate followed as As > Pb > Cd > Zn. Both limestone and cement raw meal have been demonstrated the capability to mitigate the rates of heavy metal volatilization. Notably, cement raw meal displays a more pronounced effect compared to limestone in suppressing volatilization processes. Over 50% of heavy metals were transformed into residual state at 1400 °C, and Cd, As and Zn were easy to be solidified than Pb. A pilot scale experiment proved that more than 80% of heavy metals was solidified, and Zn reached nearly 100%. Moreover, around 80% of Cd, As and Zn were remained in clinker and the rest was distributed in kiln dust particles, only very few amount was released into the exhaust flue gas. This study provides a comprehensive and extensive understanding of the volatilization characteristics and migration patterns of heavy metals in the cement kiln environment. It offers theoretical support for the control of heavy metals during the co-processing of hazardous solid waste in cement kilns.

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.

Uncertainties in Pollution and Risk Assessments of Heavy Metals in Lake Sediments Using Regional Background Soils in China.

Background soils are frequently utilized as a surrogate to assess pollution levels and environmental risks of heavy metals in Chinese lakes. However, there remains a lack of understanding regarding the reliability and uncertainty of such assessments. Here, we determined heavy metals (As, Cd, Co, Cr, Cu, Hg, Ni, Pb, and Zn) in sediment cores from five rural lakes in North China to evaluate the reliability and uncertainty of the assessments using background soils by comparing them with assessments based on background sediments. Comparative studies reveal large uncertainties in the assessments using background soils. Among these metals, uncertainties for Hg and Cd are relatively large, whereas those for the other metals are minor. This discrepancy is due to the considerably higher natural variability of Hg and Cd in soils and sediments in comparison to the other metals. Generally, assessments utilizing background soils underestimate pollution levels and risks of Hg but overestimate those of Cd in these lakes. Despite limited human activities around the lakes, they still received a considerable influx of heavy metals via regional atmospheric transport. Assessments of the nine metals indicate moderate to considerable ecological risks in these lakes. The risks are contributed primarily (78-89%) by Hg and Cd. This study underscores the substantial uncertainties in assessing heavy metal pollution and risks using regional background soils and emphasizes the importance of controlling atmospheric emissions of Hg and Cd to mitigate pollution in rural and remote water bodies in China.

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.

Parasitological indicators, haemato-biochemical alternations, and environmental risks of heavy metals in cultivated and wild freshwater catfish, Egypt

Parasitological indicators, haemato-biochemical alternations, and environmental risks of heavy metals in cultivated and wild freshwater catfish, Egypt

Occurrence, Bioavailability, and Environmental Risk of Heavy Metals and Metalloids in the Sediment and Drawdown Area of Fengshuba Drinking Water Reservoir

ABSTRACT Heavy metal and metalloid pollution in reservoir systems has attracted widespread attention due to their toxic, persistent, and nonbiodegradable characteristics. This study investigated the distribution and risks of heavy metals and metalloids in the sediment and drawdown area of the Fengshuba reservoir system. Sediment phase exhibited substantial heavy metal and metalloid pollution and higher ecological risk that the drawdown phase. There were significant differences in the structure and composition of the total metal content and the bioavailable fraction between the sediment and the drawdown area, which indicates that the total metal content and the bioavailable fraction might dominantly regulate by a complex combination of sediment characteristics. Positive Matrix Factorization model was used to identify sources of heavy metals and metalloids pollution and revealed that heavy metals and metalloids contamination in Fengshuba reservoir might originate from anthropogenic activities. Evaluations from risk assessment show that As and Cd in the reservoir system may pose health risks. Knowledge of distribution, potential risk assessment, and source apportionment of heavy metals and metalloids in the Fengshuba drinking water is critical in promoting the sustainable development of the reservoir, developing water management and conservation strategies in the Fengshuba reservoir.

Influence of the freeze–thaw process on coal gangue–based ecological restoration materials: performance and ecological risk assessment of heavy metals

Materials made from coal gangue (CGEr) can be used for ecological restoration in mining areas. This paper comprehensively analyzed the influence of the freeze-thaw process on the performance of CGEr and the environmental risk of heavy metals. The safety of CGEr was assessed by sediment quality guidelines (SQGs), geological accumulation index (Igeo), potential ecological risk index (RI), and risk assessment code (RAC). The freeze-thaw process reduced the performance of CGEr, that the water retention of CGEr decreased from 1.07 (g water/g soil) to 0.78 (g water/g soil), and the loss rate of soil and water increased from 1.07 to 4.30%. The freeze-thaw process reduced the ecological risk of CGEr, the Igeo of Cd and Zn decreased from 1.14 to 0.13 and 0.53 to 0.3, respectively, and the RI of Cd decreased by 50% from 0.297 to 0.147. Reaction experiments and correlation analysis showed that the freeze-thaw process destroyed the pore structure of the material, resulting in the degradation of its properties. Water molecules undergo phase transformation during freeze-thaw, and particles were squeezed by ice crystals to form agglomerates. The formation of granular aggregates resulted in the enrichment of heavy metals in the aggregates. Influenced by the freeze-thaw process, specific functional groups such as -OH were more exposed on the surface of the material, which affected the occurrence form of heavy metals and thus reduced the potential ecological risk of the material. This study provides an important basis for the better application of ecological restoration materials of CGEr.

Transformation and environmental risk of heavy metals in sewage sludge during the combined thermal hydrolysis, anaerobic digestion and heat drying treatment process.

The design of this study was to investigate the solid-aqueous migration and chemical speciation transformation of heavy metals (HMs) in the sewage sludge during the combined process of thermal hydrolysis, anaerobic digestion and heat-drying. The results showed that most of the HMs were still accumulated in the solid phase of various sludge samples after treatment. After thermal hydrolysis, the concentrations of Cr, Cu and Cd increased slightly. All the HMs measured after anaerobic digestion were concentrated obviously. While the concentrations of all HMs decreased slightly after heat-drying. The stability of HMs in the sludge samples was enhanced after treatment. The environmental risks of various HMs were also relieved in the final dried sludge samples.

ERT-assisted assessment of geochemical characteristics of tailings profile and environmental risks of heavy metals: a study on a typical sulfide tailings pond

ERT-assisted assessment of geochemical characteristics of tailings profile and environmental risks of heavy metals: a study on a typical sulfide tailings pond

Estimation of Probabilistic Environmental Risk of Heavy Metal(loid)s in Resuspended Megacity Street Dust with Monte Carlo Simulation

To improve the ecological environment quality of industrial cities and protect the health of residents, we determined the priority control factors of heavy metal(loid)s (HMs) pollution and risk in the resuspended street dust (RSD) of Shijiazhuang, an emblematic heavy-industrial city in North China, according to the probabilistic risk assessment method. The results showed that the HMs studied in Shijiazhuang RSD exhibited different pollution levels, that is, Hg showed moderate-to-severe pollution and above; Zn showed moderate-and-above pollution; Co, Cu and Pb showed non-pollution to moderate pollution; while As, Cr, Mn and Ni showed no pollution. The overall contamination of HMs in the RSD presented moderate-to-above contamination levels in &gt;94% of samples. Mercury exhibited considerable-to-very-high ecological risk. The synthetic ecological risks of the HMs were considerable-to-above. The comprehensive pollution and synthetic ecological risk of HMs in Shijiazhuang RSD were mainly caused by Hg. The carcinogenic risk of HMs in RSD to local inhabitants and their non-carcinogenic risk to children should not be ignored. Coal-related industrial sources are a priority source to control. Hg and As are priority HMs to control. We suggest that local governments should strengthen the management of coal-related industrial sources and As and Hg emissions.