BCR Extraction Research Articles

Fe‐Mn oxide, microbe and biochar composite for remediation of Cd and As co‐contaminated water and soil

AbstractThe novel Fe‐Mn oxide, microbe and biochar composite (FM‐DB) synthesized by mixing Fe‐Mn oxide, Cd(II)‐resistant microbe inoculated biochar, was to simultaneously remediate the co‐contamination of Cd and As. The adsorption behaviour and mechanism of Cd(II) and As(III) were studied by using adsorption experiments: the effects of the initial pH of solution, initial concentration of heavy metal, and addition order of Cd(II) and As(III) solutes on adsorption of FM‐DB. The adsorption capacity for Cd and As was 59.27 and 84.73 mg·kg−1, respectively. The results showed both antagonism and synergistic interaction behaviour of Cd(II) and As(III) adsorption. Synergistic effects was primarily governed by electrostatic interaction, biochemistry/specific adsorption and Cd‐As co‐precipitation. To investigate the FM‐DB stabilization ability of heavy metal in two paddy soils, a 60‐days soil incubation experiment was carried out. The pH of SY was significantly increased by 0.39–1.21 units with FM‐DB addition, and the pH of FS remained relatively stable throughout the incubation periods. FM‐DB significantly increased the DOC of the two soils by 40.57% and 18.16%, respectively. The BCR extraction was employed in this study to assess the transformation of unstable Cd and As into residual fractions. FM‐DB significantly decreased the concentration of available Cd and As by 6.7%–20.4% and 8.7%–24.3%, respectively in SY, and by 4%–8% and 5.4%–25.2%, respectively in FS (p < .05). Thus, it is feasible to apply FM‐DB to alleviate the Cd and As pollution in the environment.

Distribution and transformation of potentially toxic elements in cracks under coal mining disturbance in farmland.

The ground cracks resulting from coal mining activities induce alterations in the physical and chemical characteristics of soil. However, limited knowledge exists regarding the impact of subsidence caused by coal mining on the distribution of potentially toxic elements (PTEs) fractions in farmland soil. In this study, we collected 19 soil profiles at varying depths from the soil surface and at horizontal distances of 0, 1, 2, and 5m from the vertical crack. Using BCR extraction fractionation, we determined the geochemical fractions and total concentrations of Chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd) and lead (Pb) to investigate their ecological risk, spatial fraction distribution, and main influencing factors. Results showed that the values of Cd appearing in 68.7% of the samples were higher than 40 and less than 80, presented a moderate ecological risk. Chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), and lead (Pb) were mainly bound to residual fractions (> 60%) with lower mobility and Cd was dominated by F1 (acid-soluble fractions, 50%) and F2 (reducible fractions, 29%) in surface soil (0-20cm). The geochemical fractionation revealed that the mobile fractions (F1-acid-soluble and F2-reducible) of PTEs were primarily located near the crack, influenced by available potassium. In contrast, the less mobile fractions (F3-oxidizable and F4-residual) exhibited higher concentrations at distances of 2 and 5m from the crack, except for arsenic, influenced by the presence of clay particles and available phosphorus.

Investigating the elemental composition of Egyptian glauconite sediments by applying BCR sequential extraction procedure and some single extractants

This study assesses the elemental composition of Egyptian glauconite sediments, focusing on potentially toxic elements (PTEs) and macronutrients. The primary aim is to evaluate the feasibility of utilizing these sediments as a natural source of potassium for agricultural purposes, besides conventional chemical fertilizers like potassium sulfate. To quantify elemental content, chemical analysis was employed across five distinct grain size fractions after grinding glauconite rock. The assessment included potassium, calcium, sodium, and PTE concentrations, utilizing potassium chloride (KCl) and ammonium acetate lactate (AL Solution) as single extractants, and the BCR extraction protocol, in addition to measuring the pseudo-total content of these elements. Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) facilitated a comparative analysis of elemental concentrations. Results indicate PTE concentrations within European Union regulations, with an absence of cadmium. Glauconite samples contain approximately 3–3.3% potassium by weight, alongside significant amounts of essential macronutrients (calcium, magnesium) and micronutrients (copper, nickel, zinc) crucial for agriculture. BCR sequential extraction protocol results closely align with or slightly surpass pseudo-total content results. Notably, the AL Solution demonstrates high efficiency compared to KCl or acetic acid in the first step of the BCR method. BCR sequential protocol provides valuable insights into various elemental forms and potential mobility. Overall, this study reveals that glauconite has the potential to serve as a promising alternative potassium fertilizer without causing adverse environmental impacts.

Fate, source apportionment and fractionation of potentially toxic elements in agricultural soil around a densely populated, semiarid urban center of India: baseline study and ecological risk assessment.

This study is on the outskirts of the rapidly growing city of Jaipur, located in the semiarid region of India and gateway to the 'Great Indian Thar' desert, and focused on potentially toxic elements (PTE) pollution in the farmlands around the city. Concentrations of PTE, along with associated soil parameters such as pH, available nitrogen, organic carbon, phosphorus, and potassium, were estimated in agricultural soil samples near an industrial region on the outskirts of the capital city of the largest state of India. The PTE concentrations in the soil were in the following order: Mn > Pb > Ni > Cr > Cu > Cd. Soil pollution indices, such as the geochemical accumulation index (Igeo), contamination factor (CF), and ecological risk index (ERI), indicated that the soil was moderately to highly polluted. The result of BCR extraction techniques showed Cd is found mainly in the exchangeable and residual fractions, Pb, Mn were found in the reducible as well as residual fractions, while other PTE were mostly bound to residual fraction. All other PTEs are primarily found in the residual fraction, tightly linked with the silicate lattice of soil minerals. Multivariate analysis and the Pearson correlation matrix indicate a common source apportionment for Pb and Cd. Cd, and Pb concentrations in agricultural soil indicate ecological harm that warrants immediate attention and policy-level intervention.

Effects of Different Passivating Agents on Cd Pollution in Alkaline Farmland Soil

In this study, cadmium-polluted farmland in the southern suburbs of Jiaozuo, Henan Province was selected as the research object. Under the field conditions, two passivating agents such as aluminosilicate and calcium-aluminum hydrotalcite were added respectively, and the cadmium form content was analyzed by BCR extraction method. The passivating effect of different passivating agents on soil cadmium in alkaline farmland in northern China was studied under the application rate of 200 and 400kg/mu. The results showed that silicoaluminate and calcium-aluminum hydrotalcite reduced soil pH value in different degrees, but had little effect on soil pH value. The two passivating agents can convert the soluble Cd of weak acid to the residual Cd, and the transformation effect is more significant with the increase of the applied amount. The passivation effect is ranked as calcium aluminum hydrotalcite > silicaluminate, among which 400 kg/mu of calcium aluminum hydrotalcite has the most obvious passivation effect, and the effective content of Cd is reduced by 70.5% compared with group CK. In general, after the application of two passivators and different amounts, the soluble Cd content of weak acid in soil decreased significantly, the reducible Cd content decreased slightly, the oxidizable Cd content increased slightly, and the residual Cd content increased significantly.

Evaluation of Total Concentrations and Extractable Fractionations of Cd, Co and Ni in Soils from Dumpsites across Rivers State, Nigeria

The mobility of trace metals in soils strongly depends on the forms in which the metals are bound to major soil components. This study aims to determine the total concentrations and extractable fractionations of Cd, Co and Ni in soil samples collected from dumpsites across Rivers State, Nigeria. Solar Thermo Elemental Atomic Absorption Spectrometer model (SG 71906) was used after mixed acid digestion (HCl: HNO3 in a ratio of 3:1 v/v) and modified BCR sequential extraction procedure. The concentration levels of Cd, Co and Ni in all the samples varied, with mean values of 13.48 11.85, 25.29 17.62 and 20.52 15.66 mg/kg, respectively. Using the Community Bureau of Reference (BCR) sequential extraction procedure, the elements recoveries were within the acceptable range varying between 92.10% and 98.33% for Co and Cd, respectively. Data from the BCR extraction procedure revealed that the majority of Cd fraction was associated with residual fraction, Co fraction bound to the exchangeable fraction, while Ni was found to be associated with oxidisable fraction. These results suggest that the trace elements in the soil were highly mobile and bioavailable for plant uptake. Results from the findings particularly correlation analysis is indicative of the fact that some of the contaminants may have anthropogenic and natural origin. Hence, these contaminants could pose significant threat to human health and the environment.

Surface-loaded magnesium and phosphorus-modified lignite adsorbents: Efficient adsorption and immobilization for remediation of Cd-contaminated water and soil

Lignite is a resource-rich material with favorable adsorption properties and can be used as an environmentally friendly material for removing heavy metals. In this study, we loaded magnesium and phosphate ions onto the surface of lignite (LM) by using chemical modification to generate modified lignite materials, Mg-LM and P-LM, which were used for the adsorption and immobilization of Cd (II) in polluted water and soil. Characterization analysis showed the introduction of exchangeable Mg ions and enhancement of the pore structure in Mg-LM; the increase in the number of oxygenated functional groups and, exchangeable calcium ions and P content of P-LM may favor the adsorption and immobilization of Cd (II). Cd (II) adsorption on Mg-LM and P-LM was consistent with the pseudo-secondary kinetics and Langmuir isotherm models. The maximum adsorption capacity of Cd (II) on Mg-LM and P-LM was 1033 mg/g and 55 mg/g, respectively. The reduction in the soil DTPA-Cd content (32.9%) was greater under P-LM treatment than under Mg-LM (20.2%) and LM (11.1%) treatments. In addition, successive BCR extractions confirmed that Mg-LM and P-LM promoted the transformation of unstable Cd fractions to stable Cd fractions in the soil. The XRD, FTIR, and XPS results indicated that electrostatic interactions, ion exchange, surface complexation and precipitation might be the main mechanisms involved in the adsorption and immobilization of Cd (II) by Mg-LM and P-LM. Our results suggest that Mg-LM is more suitable than P-LM for the remediation of Cd-contaminated water, and less applicable than in Cd-contaminated soil.

Distribution, source and contamination of rare earth elements in sediments from lower reaches of the Xiangjiang River, China

Rare earth elements (REEs) are emerging micropollutants in aquatic environments. In this study, concentrations of REEs and major elements, and mineralogical compositions of sediments from lower reaches of the Xiangjiang River (China) were analyzed using ICP-MS technique. The results suggested that sediments were characterized by terrigenous compositions TiO2, SiO2, Al2O3, K2O, Na2O and P2O, and contained high concentrations of REEs with mean total REE concentrations (∑REE) of 318.7 mg/kg. REEs were moderately enriched in upper river sediments, and slightly or less enriched in downriver sediments. The normalized REE distribution pattern for sediments was characterized by flat shalelike and Eu depleted V-shape REE patterns, which indicated REEs in sediments were lithologically contributed from sedimentary rocks and granites distributed in the watershed respectively. REEs in sediments were hosted mainly in Fe–Mn oxides, and sulfide and organic matters that were characterized by middle REEs (MREE) enrichments relative to light REEs (LREE) and heavy REEs (HREE), and the distribution and differentiation of REEs in sediments were controlled by clays, Fe–Mn oxides, organic matters and finer grains; and also by accessory minerals (e.g., zircon) from granite. The distribution features of REEs in sediments and BCR extraction results suggested that the sediment REE enrichment resulted from additional REE input from anthropogenic sources, including those in discharges from sulfide-ore smelting industries at Zhuzhou city and from phosphate fertilizer plants at Xiangtan city along the river. Thus, sediments were contaminated with REEs in moderate degree in upper river area, and REE contamination was then formed by superimposing anthropogenic REEs on lithological residues. Finally, concentrations of Ce > 100 mg/kg, Gd > 8.12 mg/kg, ∑REE >274.9 mg/kg, ∑LREE >252.3 mg/kg and ∑HREE >28.8 mg/kg here were recommended as the REE contamination levels that represented as REE indices for identifying and rating REE contamination in this mining impacted river.

Environmental bioavailability of arsenic, nickel and chromium in soils impacted by high geogenic and anthropogenic background contents

High arsenic, chromium and nickel in soils can pose a hazard to the ecosystem and/or human health. Large areas can be affected by elevated potentially toxic elements (PTE) background contents, entailing a significant effort for managing the potential risk. Assessing the environmental hazard associated to PTE-contaminated soils requires the determination of soil PTE environmental bioavailability, which reflects the capacity of these elements to be transferred to living organisms. Here we assess the environmental bioavailability of As, Cr and Ni in topsoils from the Liège basin and Belgian Lorraine, two areas in Wallonia, Belgium, affected by elevated As, Cr and Ni background contents. The source of soil As, Cr and Ni differs in Liège and Lorraine: anthropogenic in the former location and geogenic in the latter. The environmental bioavailability of PTE was determined using two complementary approaches: (1) by chemical fractionation with the Community Bureau of Reference (BCR) three-step sequential extraction protocol and (2) by estimating the phytoavailability using a plant-based biotest (Lolium multiflorum as plant model). The results show that total As (6–130 mg·kg−1), Cr (15–268 mg·kg−1), and Ni (8–140 mg·kg−1) contents in the Liège and Lorraine soils frequently exceed the soil clean-up standards. However, no positive correlation was found between the total contents and BCR extraction results or rye-grass contents, except for As in Liège soils. Total As, Cr or Ni contents surpassing soil standards do not necessarily result in elevated mobile, potentially mobilizable and phytoavailable contents. In general, environmental bioavailability of As, Cr and Ni is higher in soils from Liège basin compared to those sampled in Belgian Lorraine. The mobile and potentially mobilizable fractions of As, Cr and Ni account for <30 % of their total contents following the BCR extractions. Our study provides valuable information for sustainable management at the regional scale of soils containing high PTE contents.

Remediation of vanadium contaminated soils in a waste smelter by eco-friendly chitosan@mineral composites

The immobilization of vanadium(V) on the soil via green materials like chitosan (CS) and minerals is an eco-friendly remediation technique. In this study, chitosan cross-linked attapulgite (ATP), bentonite (BT) and hydroxyapatite (HAP) composites (CS@ATP, CS@BT and CS@HAP) were prepared and applied to the V contaminated soils in a waste smelter. To reveal the influence of various factors on the stabilization effect, batch and European Community Bureau of Reference (BCR) extraction tests were carried out. The results indicated that the stabilization efficiency of 6% CS@ATP, CS@BT and CS@HAP on V reached 75.47%, 68.93% and 67.94%, respectively. Soil moisture content and dry–wet alternating environment have influence on stabilization to some extent. Langmuir and pseudo-second-order kinetic models were more suitable for the immobility process of V by the composites. After stabilization, the porosity, pH, cation exchange capacity (CEC) and soil organic matter (SOM) of soil increased, which improved soil fertility. The BCR extraction test indicated the acid soluble (AC), reducible (RE) and oxidizable (OX) fractions of V decreased, while the residual fraction (RES) increased obviously. In general, the stabilizers had excellent remediation effects on V polluted soil. The main stabilization mechanism is that amino groups and other oxygen-containing groups such as hydroxyl form complexes with V. Overall, the work provided some valuable ideas for the remediation of V contaminated soil by environmentally friendly materials.

Geochemical fractionation, bioaccessibility and ecological risk of metallic elements in the weathering profiles of typical skarn-type copper tailings from Tongling, China

Nonferrous metal tailings have long posed a significant threat to the surrounding environment and population. Previous studies have primarily focused on heavy metal pollution in the vicinity of sulfide tailings, while little attention was given to metal mobility and bioavailability within skarn-type tailings profile during weathering. Therefore, this study aimed to investigate the fractionation, bioaccessibility, and ecological risk associated with metallic elements (MEs, including Pb, Cd, Cr, Zn, and Cu) in two representative weathering copper-tailings profiles of Tongling mine (China). This was achieved through the use of mineralogical analyses, BCR extractions (F1: exchangeable, F2: reducible, F3: oxidizable, F4: residual fraction), in-vitro gastrointestinal simulation test (PBET) and risk assessment models. The mineral compositions of two weathering profiles were similar, with quartz and calcite being the dominant minerals, along with minor amounts of siderite, hematite and spangolite. The mean concentration in the tailings profile was approximately 0.31 (Cr), 1.8 (Pb), 12 (Zn), 33 (Cd) or 34 (Cu) times of the local background values (LBVs). The mean content of the bottom weakly-weathering layer in profile was about 0.36 (Cr), 0.91 (Pb), 1.91 (Cd), 2.73 (Zn) or 2.68 (Cu) times of the surface oxide layer, indicating a strong weathering-leaching effect. The average proportion of BCR-F1 fraction for Cd (30.94 %) was the highest among the five MEs, possibly due to its association with calcite. The PBET-extracted fractions for Cd, Zn and Cu were significantly positively correlated with the F1, F2 and F3 fractions of BCR, suggesting that these elements have higher bioavailability/bioaccessibility. The assessment results indicated that Cd posed a higher health risk, while the risk of Cu, Zn, and Pb is relatively low and Cr is safe. In conclusion, this study provides valuable insights into the environmental geochemical behavior and potential risks of MEs in skarn-type non-ferrous metal tailings ponds.

Pig manure biochar for contaminated soil management: nutrient release, toxic metal immobilization, and Chinese cabbage cultivation

Pig manure could be an effective fertilizer source for soil, but with high concentrations of xic elements. It has been shown that the pyrolysis method could largely reduce the environmental risk of pig manure. However, the comprehensive analysis of both toxic metals immobilization effect and environmental risk of pig manure biochar applied as a soil amendment is rarely addressed. To address the knowledge gap, this study was carried out with pig manure (PM) and pig manure biochar (PMB). The PM was pyrolyzed at 450 ℃ and 700 ℃, the corresponding biochar was abbreviated as PMB450 and PMB700, respectively. The PM and PMB were applied in a pot experiment growing Chinese cabbage (Brassica rape L. ssp. Pekinensis) with clay-loam paddy soil. The application rates of PM were set at 0.5% (S), 2% (L), 4% (M) and 6% (H). With the equivalent mass principle, PMB450 and PMB700 were applied at 0.23% (S), 0.92% (L), 1.84% (M), 2.76% (H), and 0.192% (S), 0.7% (L), 1.4% (M), 2.1% (H), respectively. Parameters of Chinese cabbage biomass and quality, total and available concentrations of toxic metals in soil, and soil chemical properties were systemically measured. The main results of this study showed that compared with PM, PMB700 was more effective than PMB450, which induced the highest reductions of Cu, Zn, Pb, and Cd contents in cabbage by 62.6%, 73.0%, 43.9%, and 74.3%, respectively. Both PM and PMB increased the total contents of metals (Cu, Zn, Pb, and Cd) in soil, and PMB decreased the mobility of Cu, Zn, Pb, and Cd at high application rates (≥2%). Treatment with H-PMB700 reduced CaCl2 extractable Cu, Zn, Pb, and Cd by 70.0%, 71.6%, 23.3%, and 15.9%, respectively. For Cu, Zn, Pb, and Cd fractions with BCR extraction, PMB treatments, especially PMB700, were more effective than PM in decreasing the available fractions (F1 +F2 +F3) at high application rates (≥2%). Overall, pyrolysis with high temperature (e.g., 700 ℃) could significantly stabilize the toxic elements in PM and enhance PM’s effect on toxic metals immobilization. The marked effects of PMB700 on toxic metal immobilization and cabbage quality improvement might be attributed to high ash contents and liming effect.

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

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

Leaching characteristics and potential risk assessment of heavy metals Pb-Cd from mining soils in an acid rain environment

To investigate the pollution characteristics of Pb and Cd in mining soil, dynamic leaching tests was conducted to explore the leaching characteristics. Pollution was evaluated using the Risk Index (RI) and Assessment Code (RAC). The results showed that under simulated acid rain, the soil had a certain buffer capacity, the pH value of leaching solution varied between 5.0 and 8.5. Heavy metals release also varied, with the highest amount of Pb dissolved being 2.27 mgꞏL-1, while that of Cd was relatively low, the highest is 0.93 mgꞏL−1. Moreover, heavy metals with larger particle sizes showed a greater propensity for dissolution when subjected to acid rain. BCR extraction revealed that the initial heavy metal status was mostly residual. After leaching, heavy metal morphology changed drastically, with the residual state of reducing significantly. RAC and RI indicated a moderate risk of Pb and Cd pollution under different treatment conditions.

Pinus halepensis in Contaminated Mining Sites: Study of the Transfer of Metals in the Plant-Soil System Using the BCR Procedure.

The study aimed at evaluating the geochemical fractions of Zn, Pb, Cd and their bioavailability in soil in-depth and around the root of Pinus halepensis grown on heavily contaminated mine tailing in south-western Sardinia, Italy. The contaminated substrates were partly investigated in a previous study and are composed of pyrite, dolomite, calcite, quartz, gypsum, barite, iron-sulfate and iron-oxide. The geochemical fractions and bioavailability of Zn, Pb and Cd were measured through the BCR extractions method. Cadmium in the superficial contaminated substrates was mainly found in the exchangeable BCR fraction. Zinc and lead were often found in the residual BCR fraction. PCA confirmed that the uppermost alkaline-calcareous layers of mine waste were different with respect to the deeper acidic layers. We demonstrated that Pb and Zn were less present in the exchangeable form around the roots of P. halepensis and in soil depth. This can be due to uptake or other beneficial effect of rhizospheres interaction processes. Further studies will shed light to confirm if P. halepensis is a good candidate to apply phytostabilization in mine tailing.

Elevated Urbanization-Driven Plant Accumulation of Metal(loid)s Including Arsenic Species and Assessment of the Kłodnica River Sediment Contamination

The impact of water and bottom sediment pollution of a river subjected to a strong industrial anthropogenic pressure of metal(loid) (including arsenic and its species) accumulation in riverbank plants such as Solidago virgaurea L., Phragmites L. and Urtica dioica L. was investigated. The high-performance liquid chromatography-inductively coupled plasma-mass spectrometry (HPLC-ICP-MS) technique was used to study organic and inorganic arsenic species in selected plants and their response to heavy metal and arsenic contamination. The modified BCR extraction results showed that arsenic was mainly bound to the mobile reducible and organic-sulfide fractions in the Kłodnica River bottom sediments. Research has shown that the bottom sediments of the Kłodnica River are contaminated with metals, including Pb, Zn, Ni, As, and among arsenic species, the As(V) form dominated quantitatively, with its highest concentration being 49.3 mg kg−1 and the organic species occurred extremely rarely. The highest concentration of arsenic, among the tested plants, occurred in Phragmites communis L. The evaluation of the bottom sediment pollution was performed using Sb/As factor, geoaccumulation index (Igeo), enrichment factor (EF) and pollution load index (PLI). The ability of the plant to assimilate metals from the substrate was studied by calculation of the bioaccumulation factor (BAF). Values of the Igeo change in a wide range from class 1 (uncontaminated to moderately polluted for Cu and Zn) at the first sampling point, to 5 (highly to extremely polluted for Ba and Fe) at the K4 sampling point. The Igeo results show an increase in the contamination with elements toward the runoff of the Kłodnica River.

Distribution and ecological risk assessment of heavy metals in sediments of Dajiuhu Lake Wetland in Shennongjia, China.

The rapid development of modern society has resulted in discharge of large, heavy metal quantities into wetlands that have been continuously accumulating, causing severe pollution. Dajiuhu, located in the Shennongjia Forest District of Hubei Province in China, is a wetland of significant value internationally, serving as a model wetland ecosystem with heightened scientific research value. In this study, 27 surface sediment samples from nine sub-lakes in Dajiuhu were collected in August 2020. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the sediments were determined. The heavy metal occurrence and speciation characteristics were analyzed by an improved BCR (European Community Bureau of Reference) extraction method. Four methods were used to evaluate heavy metals' pollution degree and ecological risk. The possible source of heavy metals was inferred using correlation analysis and principal component analysis. The heavy metal content in the lake sediments of Dajiuhu wetland was from the highest to the lowest concentration as follows: Zn [Formula: see text] Cr [Formula: see text] Ni [Formula: see text] Pb [Formula: see text] Cu [Formula: see text] Cd. The average Cd content exceeded the national nature reserve threshold values, while the other heavy metals measured were below their respective threshold values. However, due to the occurrence of Pb and Cd in different forms, they still pose certain pollution and ecological risk to the lake wetlands. On the other hand, Zn, Cr, Ni, and Cu do not pose an ecological risk in the lakes of the Dajiuhu wetland. The spatial distribution of heavy metal content in the nine sub-lakes did vary significantly. Regarding the heavy metal sources in the lake sediments, Ni, Cr, and Cu originate from natural factors, and Cd and Pb have mainly anthropogenic origins. In contrast, Zn has both natural and anthropogenic origins. This study provides further insights into the study of heavy metal pollution in lake wetlands. It provides a framework and a direction for managing heavy metal pollution in the Dajiuhu wetland.

Metal contamination in sediments of dam reservoirs: A multi-facetted generic risk assessment

The quality of bottom sediments is a key factor for many functions of dam reservoirs, which include water supply, flood control and recreation. The aim of the study was to combine different pollution indices in a critical generic risk assessment of metal contamination of bottom sediments. Both geochemical and ecological indices reflected that sediment contamination was dominated by Zn, Pb and Cd. The ecological risk indices suggested a high riks for all three metals, whereas human health risks were high for Pb and Cd. An occasional local contamination of sediments with Cr and Ni was revealed, although at levels not expected to cause concerns about potential ecological or health risk. Sediments from the Rybnik reservoir for Cu only revealed a high potential ecological risk. EF turned to be as being the most useful, whereas TRI (∑TRI) was the most important ecological index. All multi-element indices suggested similar trends, indicating that Zn, Pb and Cd taken altogether had the greatest impact on the level of sediment contamination and posed the greatest potential ecological and health risks to organisms. The use of sequential BCR extraction and ecotoxicity analyses allowed for a multi-facetted generic risk assessment of metals in sediments of dam reservoirs.

Speciation and Risk of Heavy Metals in Surface Sediments of Different Types of Water Bodies in Baiyangdian Lake

The morphological characteristics of Cd, Cr, Cu, Ni, Pb, and Zn in sediments were analyzed using an improved BCR extraction method in four water types of Baiyangdian Lake:watercourse, trench, lake surface, and fish pond. The potential ecological risk index, secondary and primary phases, and risk assessment codes were used to systematically assess the pollution level and ecological risk of heavy metals in surface sediments. The results showed that:① the mean contents of heavy metals Cd, Cu, and Zn in the sediments were 0.37, 28.49, and 83.08 mg·kg-1, respectively, 94.91%, 73.91%, and 46.39% of which exceeded the soil background value. ② Cd was dominated by the non-residual fraction (F1+F2+F3) with a fraction ranging from 54% to 97%, whereas Cr was dominated by the residual fraction (F4) with a mass fraction ranging from 87% to 99%. Cu, Ni, Pb, and Zn were mainly in the fraction of residual fraction. In the non-residual fraction, Cu and Ni were mainly in the oxidizable fraction (F3) state, whereas Pb and Zn were mainly in the reducible fraction (F2) state. ③ The RAC risk assessment results showed that there were 68.97%, 39.89%, 54.84%, and 49.78% points in channel, trench, open water, and fish pond samples, respectively, of Cd at high risk. The Cu, Ni, and Pb were at low risk. In general, the overall heavy metal pollution level in Baiyangdian Lake was low, but Cd had ecological risk and high bioavailability in the Fuhe River of the Nanliuzhuang area and the Baigouyin River.

Development of chitosan-magnetic sawdust hydrochar for Pb and Zn immobilization process on various soil conditions

A series of 60-day soil immobilized incubations were performed to explore the impacts of various factors (incubation time, chitosan modified magnetic sawdust hydrochar (CMSH) dosages, initial pH values, moisture contents, and humic acid (HA)) on CMSH immobilization of Pb and Zn. DTPA and BCR extraction techniques were undertaken to study the distribution of form transformations of Pb and Zn. CMSH showed significant immobilization ability for both DTPA-Pb and DTPA-Zn, and the highest removal rates were shown to be 57.40% and 90.00% for Pb and Zn respectively. After 60days of incubation, the residual Pb was enhanced by 34-61% and residual Zn increased by 25-41%, which indicated that CMSH was effective in immobilizing Pb and Zn. Meanwhile, the immobilization efficiency improved with increasing incubation time, CMSH dosage, HA dosage, and initial solution pH. In particular, 5% HA application increased the soil TOC and accelerated the metal stabilization processes, with the residual forms of Pb and Zn eventually reaching a maximum of 73% and 71%, respectively. In addition, the alkaline initial solution promoted the ion exchange, surface complexation reaction, and cationic-π interaction, resulting in a better immobilization of Pb and Zn by CMSH. Finally, according to the orthogonal analysis of BCR results, HA dosage was the major factor affecting Pb and Zn immobilization by CMSH compared to soil pH and moisture content in this study.