Acid-soluble Fraction Research Articles

Bioavailability of trace metals in sediments from Daya bay nature reserve: Spatial variation, controlling factors and the exposure risk assessment for aquatic biota

Determining the ecological risk and environmental significance of trace metal bioavailability is critical for the sustainability of the marine environment and bioresources. The spatial variation, controlling factors and ecological risks of the bioavailability of trace metals (V, Cr, Ni, Cu, Zn, As, Cd and Pb) in Daya Bay sediments were analyzed using BCR sequential extraction and diffusive gradient in thin films (DGT). Differences in concentration distributions between the anthropogenic impact zone (AIZ) and the marine disturbance zone (MDZ) revealed the accumulation of anthropogenic metals in sediments, and that the ocean dynamic conditions promoted the release of bioavailable metals from nature sediments. Fine-grained sediments rich in organic matter possessed more bioavailable metals on the surface. The negative correlations between salinity and the non-residual fractions (F123) suggests that salinity has the potential to inhibit the bioavailability of trace metals. Risk assessment based on total concentrations and acid soluble fractions (F1) showed that Cd was the dominant contributing element to the potential ecological risks with 55.8 %. The evaluation via DGT-labile concentrations indicated that Cu was the element of priority concern for aquatic exposure risk with a risk probability of 7.45 %, and the joint risk probability for metal mixture toxicity was 12.27 %. The exposure risk for aquatic biota was shown as molluscs (9.37 %) > algae (6.82 %) > crustaceans (6.21 %) > invertebrates (6.07 %) > fish (2.61 %). The results provide new clues for risk assessment and management of trace metals in coastal sediments

Impact of hydrochar in stabilization/solidification of heavy metal-contaminated soil with Portland cement.

Stabilization/Solidification (S/S) using Portland cement is a common soil remediation technique for heavy metal-contaminated sites. However, due to the hindrance of cement hydration by heavy metals (HMs) and the high CO2 emissions from cement production, efforts have been made to reduce cement consumption. Supplementary cementitious materials (SCMs) present an efficient alternative for this purpose. This study investigates the impact of hydrochar and modified hydrochar as SCMs for remediating soils contaminated with Zn, Pb, and Cd. Forty treated soil samples were evaluated using unconfined compressive strength (UCS), pH, Toxicity characteristic leaching procedure (TCLP), and sequential extraction procedure (SEP) tests, and statistical analysis was conducted to assess the effects of binder content, hydrochar dosage, and hydrochar type. Results show that substituting cement with hydrochar or modified hydrochar reduces UCS by 10-40%, with hydrochar having a greater negative impact than modified hydrochar. pH values ranged from 6.98 to 12.64, facilitating HMs precipitation. In heavily contaminated samples, hydrochar or modified hydrochars significantly decreased the Zn, Pb, and Cd TCLP values by 55%, 63%, and 50%, respectively. In moderately contaminated samples, the reduction was slight for Zn and Pb, with no significant change for Cd. SEP test results indicated that hydrochar or modified hydrochar in cement improves the transformation of the acid-soluble fraction to the residual fraction of Zn and Pb, but not for Cd-contaminated soil samples. Overall, these findings suggest that incorporating hydrochar or modified hydrochar as SCMs in cement contributes to reducing cement usage and CO2 emissions while enhancing the stabilization efficiency of certain heavy metals in contaminated soils.

A Comparative Effect of Sustainable Materials on the Immobilization, Geochemical Fractions, Bioaccumulation, and Translocation of Ni in Smelter- and Mine-Polluted Soils

The present study holds significant implications, as it aims to investigate the comparative effect of biochar, zeolite, and bentonite minerals on the stabilization of Ni fractions, bioaccumulation, translocation indices, and the reduction in their absorption by pakchoi in smelter- and mine-contaminated soils. The results, which are of great interest, showed that the maximum fresh and dry biomasses of pakchoi were observed up to 28.21 and 18.43% for smelter-polluted soil and 61.96 and 67.90% for mine-contaminated soil amended with zeolite compared to the control. Applying zeolite increased pakchoi chlorophyll SPAD values 1.17-fold in smelter soil and 1.26-fold in mine-polluted soil. The highest Ni immobilization in smelter and mine soil was observed at 76.8 and 85.38% with the application of bentonite, which increased soil pH and CEC. The application of biochar, bentonite, and zeolite reduced the Ni residual, oxidizable, and acid-soluble fractions, but biochar and bentonite increased the reducible fraction of Ni in smelter soil. The highest reduction in Ni in the shoot and root was noted as 82.08 and 68.28% of smelter-polluted soil and 77.25 and 89.61% of mine-polluted soil with bentonite compared to control soil. Overall, it has been concluded that biochar, zeolite, and bentonite can be successfully used to mitigate the Ni concentration in smelter- and mine-polluted soil and reduce uptake by vegetable crops.

Geochemical Characteristics and Environmental Risks of Cu in the Soil of A Sloping Vineyard (Phu Tho Province, Vietnam)

In the vineyards, the intensive use of cupric fungicides and fertilizers has resulted in Cu enrichment in the soils. Specifically, in sloping vineyards, the mobility of Cu can contribute to intensify the environmental risks. The research on geochemical characteristics of Cu is a key solution to explore the distribution of Cu in different geochemical fractions and understand the mobility and toxicity of this element in the environment. In this study, we aim to investigate the geochemical properties of Cu in the vineyard topsoil (0-20 cm) and subsoil (20-40-60 cm), using the improved three-step sequential extraction procedure developed by the Commission of the European Communities Bureau of Reference (BCR). In addition, the environmental risk is calculated by the environmental risk code (RAC) based on the percentage of Cu in the acid-soluble fraction. The results reveal that the mobility of Cu in the acid-soluble fraction (F1) and reducible fraction (Cu associated with the iron and manganese oxyhydroxides) (F2) tends to decrease with increasing soil depth. The major portion of Cu mostly exists in the strong bond with silicate clays (F4), accounting for 84% of total Cu content on average. Contrarily, the minor propotion of Cu associates with soil organic matter (F3) (3% on average). On the other hand, the content and proportion of Cu in the soil fractions are largerly influenced by basic soil properties (organic matter contents and fine soil particles). In addition, under the impact of soil erosion, higher percentages of F1 and F2 fractions of Cu are observed in the surface soil layers at the top of the hill compared to those at the backslope of the hill. The mean calculated RAC of 10.66%, 5.76%, and 5.38% for the 0-20 cm, 20-40 cm, and 40-60 cm soil layers, respectively, demonstrate a low risk to medium environmental risk level in the studied vineyard. Although an overall low risk level is observed for Cu in the studied vineyard soil, the deposition of Cu originating from repeated Cu-based pesticides and erosion is of particular concern in the vineyard soils.

Pollution Characteristics, Risk Assessment, and Source Analysis of Heavy Metals in Soil from a Typical Abandoned Antimony Smelting Factory

Considering the surface soil （0-20 cm） from a typical abandoned antimony smelting factory area in Dachang Town, Qinglong County, Guizhou Province, as a case study, a total of 14 soil samples were systematically collected from both within and outside the smelting factory area. The analysis focused on the pollution status, distribution characteristics, and potential ecological risks of heavy metals such as Sb, As, Cd, Cr, Pb, Cu, Zn, Ni, and V in the soil. Additionally, an evaluation and analysis of pollution sources were conducted. The results showed that the mean concentrations of heavy metals including ω（Sb）, ω（As）, ω（Cd）, ω（Cr）, ω（Pb）, ω（Cu）, ω（Zn）, ω（Ni）, and ω（V） in the surface soil of the abandoned antimony smelting factory ranged from 4.58 to 15 049.33 mg·kg-1. With the exception of Cr and Ni, all values exceeded the background values of soils in Guizhou province. The single factor pollution indices of Sb and As were 83.61 and 7.01, respectively, indicating severe contamination. In contrast, Pb fell within the non-polluted to slightly polluted range. The comprehensive potential ecological risk of soil heavy metals was characterized by severe potential ecological risk levels for Sb, As, and Cd, while the remaining heavy metals fell within a range of moderate to substantial potential ecological risk levels. The assessment of the geoaccumulation index revealed that the soil in the study area was primarily contaminated by Sb and As, predominantly exhibiting contamination levels ranging from moderate to severe. The results from the RAC method suggested that Sb was the dominant focus for remediation in this abandoned smelting factory. The two primary pollutants, Sb and As, exhibited elevated levels in leachate toxicity, acid-soluble fraction, available fraction, gastric phase, and intestinal phase in terms of bioavailable content, indicating a certain potential hazard. Further, correlation analysis indicated a certain correlation between the total amount of heavy metals and leachate toxicity, available fraction, acid-soluble fraction, reducible fraction, oxidizable fraction, gastric phase extractable fraction, and intestinal phase extractable fraction. The APCS-MLR model indicated that the sources of Sb, As, Zn, Cu, and Cd were primarily industrial, while the sources of Cr and V were mainly natural, and Pb originated mainly from mixed sources.

An insight into PANI-TiO2 photocatalysis of refractory organic matter through molecular size fractionation.

Refractory organic matter (RfOM) is ubiquitous in aquatic environment and plays various roles in regulating the fate, transport, toxicity, and bioavailability of chemical species, such as metals, emerging organic contaminants, and nanomaterials. RfOM is mainly represented by humic acids (HA) as the acid insoluble fraction of organic matrix. Considering the complex and multicomponent characteristic of HA, a detailed study was designed to elucidate the fate of molecular size fractions (MSFrs) of humic under solar irradiation in the presence of polyaniline (PANI)-modified TiO2 composites. Humic acid as a consortium of diverse molecular size fractions with different tendencies towards oxidation requires further assessment by UV-vis and fluorescence spectroscopic parameters complementary to previous studies on the photocatalytic degradation of RfOM by using TiO2 and PANI-TiO2 composites. Absorbance-based removal efficiencies under initial and post-photocatalytic conditions showed a re-formation trend during photocatalysis in the presence of PANI and TiO2 where higher MSFrs were transformed to lower MSFrs that was apparent for < 3kDa fraction. Completely different profiles were observed for PT-41 and PT-81 indicating similar degradation pathways independent of PANI ratio in the composite. As confirmed by the investigated parameters, formation of both 450kDa and 220kDa MSFrs were evident under all conditions indicating in situ generation of higher MSFrs. The eligibility of coupled absorbance-fluorescence measurements to discern molecular size distribution of humic acid via oxidative degradation was also investigated. Excitation-emission matrix (EEM) contour plots emphasized the ratio dependency of PANI modification of TiO2 and revealed sample specific variations that were more pronounced in terms of the emergence of tyrosine- and tryptophan-like aromatic proteins.

Stabilization of arsenic-cadmium co-contaminated soil with the iron-manganese sludge derived amendment: Effects and mechanisms

An iron-manganese sludge-derived amendment was proposed to remediate arsenic (As) and cadmium (Cd) co-contaminated soil, with a strong adsorptive capacity across pH 4 to 10. The Langmuir model defined maximum adsorption at 78.17 mg/g for As(III), 110.48 mg/kg for As(V), and 65.77 mg/g for Cd(II). The X-ray photoelectron spectroscopy (XPS) spectra provided insights into the chemical interactions: As was predominantly complexed or ligand exchanged with iron(hydr)oxides. In contrast, cadmium exhibited a tendency to bond with acylamino and carboxyl groups, in addition to the ferric hydroxyl groups. Notably, 42.15% of the adsorbed As(III) was oxidized into As(V) by Mn(IV) oxides present in the amendment. The soil-verification experiment demonstrated that an amendment dosage of 40 g/kg was efficacious in reducing the leaching concentration of As and Cd to maintained below the safety thresholds of 0.1 mg/L and 0.01 mg/L, respectively, for pH levels 4 to 11, meeting the Chinese Surface Water Quality Standard V (GB3838-2002). After the stabilization, the exchangeable fractions of As and the acid-soluble fractions of Cd were significantly reduced, with these elements being transformed into more stable forms. The amendment maintained the soil's neutral pH and adjusted the soil physicochemical properties. This article presents a holistic approach by examining the organic-inorganic composite of iron-manganese oxides with polyacrylamide, modified as a stabilizing amendment for As and Cd co-contaminated soil. This innovative amendment adeptly navigates the previously conflicting stabilization mechanisms for anionic and cationic metals. Offering dual advantages, the amendment not only remediates soil but also addresses the disposal of waste, presenting a win-win solution for environmental management.

Unveiling The Potential of Microwave Plasma Treated Char For Sustainable Automotive Shredder Residue (ASR) Management and Reduced Ecological Risk Of Cadmium

Introduction: This study explores the effectiveness of microwave plasma pyrolysis in reducing heavy metal concentrations, specifically cadmium, in automobile shredder residue (ASR). METHOD: The ASR was subjected to plasma pyrolysis at microwave power levels ranging from 800 to 1000W, resulting in a significant decrease in heavy metal concentration in the char. Utilizing the Bureau Communautaire de Référence (BCR) sequential extraction method, a standardized procedure developed by the European Commission, we assessed the chemical speciation and matrix properties of the char. The results indicated that microwave plasma treatment effectively decreased the bioavailable forms of cadmium. After 6 minutes of pyrolysis at 1000W, the exchangeable and acid-soluble fractions (F1) dropped to 10%, while the reducible fraction (F2) fell to 12%. RESULT: This treatment resulted in a substantial increase in the oxidizable (F3) and residue (F4) fractions, which reached 27% and 51%, respectively. Importantly, the potential ecological risk of cadmium decreased significantly, with the risk index (Er) dropping from 164.91 to 28.45, aligning with Taiwan's regulatory standards for non-hazardous waste.CONCLUSION: These findings suggest that microwave plasma pyrolysis is a promising and sustainable approach for the disposal of ASR, offering an environmentally friendly alternative for waste management. This study provides valuable insights for policymakers, environmental scientists, and industries seeking effective solutions for ASR treatment.

Contamination, fraction, and source apportionment of heavy metals in sediment of an industrialized urban river in China

In this study, we conducted an analysis of the heavy metal concentrations, health risk assessment, fraction and source interpretation in surface and core sediments from main stream of the Pearl River and Pearl River Estuary (RRE) area. Results showed that the higher deposited heavy metal concentrations in sediments occur at the Pearl River. The concentrations of heavy metals in surface sediments from the studied locations are in a descending order: Zn > Cr > Cu > Ni > Pb > Cd. Regarding chemical fractions, Cd showed the highest proportion of acid soluble fraction (F1) among all studied heavy metals. The high mobility of Cd poses a significant threat to water bodies and the surrounding environment. The potential ecological risk index (RI) showed the Pearl River sediments exhibited significantly higher values than the estuary sediments. Cd was found to be the primary contributor to potential ecological risk, accounting for 74% of RI. The health risk assessment showed the total hazard index (HI) for child was exceeded 1 mainly driven by Zn, indicating that the child population was at risk of non-carcinogenic effects. Besides, unacceptable carcinogenic risk in both Pearl River and estuary area were observed for children. The positive matrix factorization (PMF) model was used to ascertain sources of six heavy metals and apportion their contributions in sediments. The results showed that the source contributions of natural, industrial, and mixed sources from coal combustion and traffic emissions accounted for 39.81%, 34.10%, 26.10%.

Comparative study of the sequential extraction methodologies for fractionation analysis of mercury in coal of Thar coalfield.

The primary objective of this study was to evaluate the bound fractions of mercury (Hg), physicochemical parameters, and mineral composition of coal. Coal samples were collected from various depths within Block-VII of the Thar coalfield in Pakistan. The Hg associated with different chemical fractions of coal was extracted using a sequential extraction scheme as per the community bureau of reference (BCR) protocol. This study utilized both the BCR-sequential extraction method (BCR-SEM) and a single-step sequential extraction based on an ultrasonic-assisted method (SSE-UAM) for the fractionation analysis of Hg in coal. The extraction methodologies, BCR-SEM and SSE-UAM, were specifically designed for analyzing Hg fractionation in coal samples. The SSE-UAM offers an operational advantage, requiring only 2h compared to the 51h needed for BCR-SEM. The analyses were validated using standard reference material (SRM-1635a) and the spiking addition method, achieving a recovery percentage of 97.1% for total Hg concentrations using the pseudo-extraction method in SRM-1635A. Total Hg content in the coal samples ranged from 0.60 to 2.34µgg-1 across four different coal seams from Block-VII of the Thar coalfield. Additionally, Hg concentration was observed to decrease with increasing depth, attributed to changes in mineralogical composition. The highest concentration of Hg was detected at a depth of 200-203m, while the lowest concentration was at a depth of 152-154m. The concentration of Hg in various fractions was 32-60% in the acid-soluble fraction, 1.72-4.92% in the reducible fraction, and 9.58-50.8% in the oxidizable fractions. The coal sample characteristics were analyzed using an elemental analyzer and scanning electron microscopy with energy-dispersive spectroscopy. Cold vapor atomic absorption spectrometry (CV-AAS) was used to measure the extracted fractional concentration of Hg in coal.

Comparative Study on the Postmortem Proteolysis and Shear Force during Aging of Pork and Beef Semitendinosus Muscles.

The differences in the proteolytic patterns and shear force of pork and beef during aging were evaluated. Pork and beef semitendinosus muscles were obtained at 24 and 48 h postmortem, respectively, and aged at 4°C for 0 (Day 0), 7 (Day 7), and 14 days (Day 14). Changes in the electrical conductivity were observed in pork on Day 7 and beef on Day 14. The calpain activity increased in pork (p<0.05) after 14 days of aging, whereas that of beef decreased on Day 7 (p<0.05). The cathepsin B activity in pork and beef increased between Day 7 and 14 (p<0.05). The content of α-amino group in the 10% trichloroacetic acid-soluble fraction increased between Day 7 and 14 in pork (p<0.05), but increased steadily in beef throughout aging (p<0.05). The electrophoretogram of the myofibrillar proteins revealed a 30 kDa protein band only in the beef lane on Day 14. The cooked pork had no significant changes in the shear force during aging periods (p>0.05), while the gradual decrease in the shear force with the increasing aging periods was shown in the cooked beef (p<0.05). Circular dichroism analysis of myosin extracts from pork and beef revealed thermal denaturation temperatures of 55°C and 58°C, respectively. This study highlights the different post-mortem proteolytic patterns and thermal denaturation temperatures of myosin in pork and beef semitendinosus muscles, which contribute to distinct changes in the shear force during aging between pork and beef.

Integrated Analysis of Pollution Characteristic and Ecotoxicological Effect Reveals the Fate of Lithium in Soil-Plant Systems: A Challenge to Global Sustainability.

Lithium, as an emerging contaminant, lacks sufficient information regarding its environmental and ecotoxicological implications within soil-plant systems. Employing maize, wheat, pea, and water spinach, we conducted a thorough investigation utilizing a multispecies, multiparameter, and multitechnique approach to assess the pollution characteristics and ecotoxicological effects of lithium. The findings suggested that lithium might persist in an amorphous state, altering surface functional groups and chemical bonds, although semiquantitative analysis was unattainable. Notably, lithium demonstrated high mobility, with a mild acid-soluble fraction accounting for 29.66-97.02% of the total, while a minor quantity of exogenous lithium tended to be a residual fraction. Plant analysis revealed that in 10-80 mg Li/kg soils lithium significantly enhanced certain growth parameters of maize and pea, and the calculated LC50 values for aerial part length across the four plant species varied from 173.58 to 315.63 mg Li/kg. Lithium accumulation in the leaves was up to 1127.61-4719.22 mg/kg, with its inorganic form accounting for 18.60-94.59%, and the cytoplasm fraction (38.24-89.70%) predominantly harbored lithium. Furthermore, the model displayed that growth stimulation might be attributed to the influence of lithium on phytohormone levels. Water spinach exhibited superior accumulation capacity and tolerance to lithium stress and was a promising candidate for phytoremediation strategies. Our findings contribute to a more comprehensive understanding of lithium's environmental behavior within soil-plant systems, particularly within the context of global initiatives toward carbon neutrality.

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.

Circadian control of histone turnover during cardiac development and growth

During postnatal cardiac hypertrophy, cardiomyocytes undergo mitotic exit, relying on DNA replication-independent mechanisms of histone turnover to maintain chromatin organization and gene transcription. In other tissues, circadian oscillations in nucleosome occupancy influence clock-controlled gene expression, suggesting a role for the circadian clock in temporal control of histone turnover and coordinated cardiomyocyte gene expression. To elucidate roles for the master circadian transcription factor, Bmal1, in histone turnover, chromatin organization, and myocyte-specific gene expression and cell growth in the neonatal period. Bmal1 knockdown in neonatal rat ventricular myocytes (NRVM) decreased myocyte size, total cellular protein synthesis, and transcription of the fetal hypertrophic gene Nppb following treatment with serum or the α-adrenergic agonist phenylephrine (PE). Depletion of Bmal1 decreased expression of clock-controlled genes Per2 and Tcap, as well as Sik1, a Bmal1 target upregulated in adult versus embryonic hearts. Bmal1 knockdown impaired Per2 and Sik1 promoter accessibility as measured by MNase-qPCR and impaired histone turnover as measured by metabolic labeling of acid-soluble chromatin fractions. Sik1 knockdown in turn decreased myocyte size, while simultaneously inhibiting Nppb transcription and activating Per2 transcription. Linking these changes to chromatin remodeling, depletion of the replication-independent histone variant H3.3a inhibited myocyte hypertrophy and prevented PE-induced changes in clock-controlled gene transcription. Bmal1 is required for neonatal myocyte growth, replication-independent histone turnover, and chromatin organization at the Sik1 promoter. Sik1 represents a novel clock-controlled gene that coordinates myocyte growth with hypertrophic and clock-controlled gene transcription. Replication-independent histone turnover is required for transcriptional remodeling of clock-controlled genes in cardiac myocytes in response to growth stimuli.

Temporal changes in the mobility of As, Pb, Zn, and Cu due to differences in biochar stability caused by lignin content

Understanding biochar aging is a critical factor in predicting its long-term effects when added to soil. This study explores the complex links between lignin content in biochar feedstock and biochar stability during accelerated aging, including its influence on heavy metal mobility in soil. In this study, nine types of biochar based on fir (F), pine (P), and oak (O) sawdust were produced at 400 °C, and lignin was extracted from them using ammonia after 0, 3, and 7 days (named as 0FB, 3FB, 7FB, 0PB, 3PB, 7PB, 0OB, 3OB, and 7OB). Subsequently, each biochar was subjected to 25 cycles of wet-dry (WD) and freeze–thaw (FT) aging. The aged low-lignin biochars (7FB, 7 PB, and 7OB) released more dissolved organic matter (DOM) and contained more oxygen-containing surface groups on their surfaces than the high-lignin biochars (0FB, 0PB, and 0OB). The low-lignin biochars with high DOM leaching released 37–85 % more anionic arsenic (As) from biochar-amended soil after 25 cycles of aging than the high-lignin biochars. The stabilities of lead (Pb), zinc (Zn), and copper (Cu) were increased due to strong binding to surface functional groups on the low-lignin biochar. The acid-soluble fractions of Pb, Zn, and Cu were converted to organic-bound fractions as biochar aging progressed, with the degree of transformation being inversely proportional to the lignin content of biochar. This research highlights the crucial role of lignin in shaping biochar stability, and reveals how biochar stability impacts soil heavy metals speciation, opening new avenues for effective biochar-based environmental solutions and the promotion of soil health.

Zinc isotope fractionation during the sorption of Zn to minerals and organic matter in sediment cores affected by anthropogenic pollution

Zinc stable isotopes (δ66Zn) serve as a widely fingerprinting tool for detecting anthropogenic Zn contamination. However, there is a limited understanding of δ66Zn behavior during the sorption of Zn to minerals and organic matter. In this study, we have determined the δ66Zn values in specific fractions to investigate their effectiveness in tracing anthropogenic Zn. The revised Community Bureau of Reference (BCR) extraction procedure was applied to a coastal marine core from Osaka Bay and from a lacustrine core from Lake Biwa, both with a history of anthropogenic metal pollution. The δ66Zn values varied from −0.14 ‰ to +1.00 ‰ across the four to five chemical fractions with up to 0.9 ‰ variation within a single horizon. The highest δ66Zn values in the acid-soluble fraction (up to +1.00 ‰) could be explained by the preferential sorption of 66Zn to carbonates and/or the preferential incorporation of 66Zn into calcite. The complex isotopic fractionation during the sorption of Zn to and co-precipitation with Fe–Mn oxyhydroxides likely resulted in an unclear pattern of the δ66Zn values of the reducible fraction. Low δ66Zn values in the oxidizable fraction (Osaka Bay) agree with the 64Zn enrichment in phytoplankton. Higher δ66Zn values of the reducible and oxidizable fractions of the Lake Biwa core indicate that environmental conditions (e.g. ionic strength) and for instance different phytoplankton species or dissolved and suspended particulate matter input drive the Zn isotope fractionation depending on the system (marine vs. lacustrine). The δ66Zn values of the acid-soluble fraction (Osaka Bay and Lake Biwa), of the reducible fraction (only Lake Biwa) and of oxidizable fraction (only Osaka Bay) better reflected the temporal changes in the Zn concentration than the bulk sediment, indicating that these fractions could be a sensitive fingerprinting tool for anthropogenic Zn contamination.

Effect of organic matter on the environmental behavior of sulfur and heavy metals in mariculture sediments during the aging process

Organic matter (OM) significantly impacts the environmental behavior of sulfur and heavy metals. In this study, the effects of OM on the migration and transformation of sulfur and heavy metals in mariculture sediments were investigated. The results indicated that baiting had a strong impact on the accumulation of acid volatile sulfur (AVS) (P < 0.05) and increased the environmental risk of sulfide in sediments. The addition of bait promoted the generation of chromium (II)-reducible sulfur (CRS); however, the resistance of AVS to CRS conversion increased with increasing bait addition. The addition of bait considerably influenced Cd accumulation. The acid-soluble fractions of Cr and Cu and the oxidizable fraction of Cd were primarily affected by the bait addition (coefficient of variation>15 %). An increase in the reducible fraction promoted the conversion of AVS to CRS, which reduced the degree of sediment aging. Higher OM levels reduced the diversity and abundance of the bacterial communities. The sulfate respiration functional microbiota was particularly affected by OM.

High-efficiency combination washing agents with eco-friendliness simultaneously removing Cd, Cu and Ni from soil of e-waste recycling site: A lab-scale experiment

Soil washing technology plays an important role in the removal of heavy metals, and the efficacy of this process depends on the washing agent used. Due to the difficulty in treating soils contaminated by multiple heavy metals, there is still a need for further exploration of efficient washing agents with low environmental impact. Although single washing agents, such as chelators, can also effectively remove heavy metals from soil, combining efficient washing agents and determining their optimal washing conditions can effectively improve their removal efficiency for multiple heavy metals in soil simultaneously. Based on the previous research, the present study was carried out to combine different types of washing agents to remediate contaminated soils at a commonly e-waste recycling site. The objectives were to investigate their efficient washing conditions and assess the impact of the washing process on the speciation distribution and pollution level associated with heavy metals in soil. The results showed that the combination of HEDP (1-hydroxyethylidene-1,1-diphosphonic acid) and FeCl3 at a ratio of 6:4 exhibited the most effective removal of Cd, Cu and Ni from the contaminated soil at an e-waste recycling site. Under optimal washing conditions, with a soil-to-liquid ratio of 1:20 and a washing time of 48 h, the removal rates of Cd, Cu and Ni were 96.72%, 69.91% and 76.08%, respectively. It needed to be emphasized that the combination washing agents were able to remove most of the acid-soluble, reducible and oxidizable fractions of heavy metals, and even the removal rates of the stable residual fraction (e.g., of Cd) was at a relatively high level. In addition, the washing process significantly reduced the pollution level associated with heavy metals in soil. This study aid in the development of combined efficient washing agents and explores optimal washing strategies for the remediation of Cd, Cu, and Ni-contaminated soil at e-waste recycling sites. The findings may play a role in enhancing the remediation capabilities for soils contaminated with multiple heavy metals, due to its characteristics of and high-efficiency and environmental friendliness.

Speciation, mobility, and risks of heavy metals in sediment and water of a freshwater Lake in Fujian Province, China

ABSTRACT This study investigated the level of dissolved heavy metals in the water of Longhu Lake and focused on the speciation, mobility, and risks of heavy metals (Cr, Mn, Ni, Cu, Zn, As, Cd, and Pb) in sediment. The levels of heavy metals in the water were found to be below the thresholds set by the Chinese safe drinking water standard. The highest average percentages of Cr, Ni, Zn, and As were bound with residual fractions, while Pb and Cu were bound with reducible fractions. Additionally, the highest percentage of Cd and Mn was bound to the acid-soluble fraction in the sediment. These findings suggest that Cd, Mn, Pb, and Cu likely originated from anthropogenic sources in the lake. There was a strong correlation between total organic carbon (TOC) and metal fractions in the sediment, indicating that TOC may play a role in transporting heavy metal fractions. Risk assessment code values for Cd and Mn indicated higher risks and mobility, while Ni, Cu, and Zn showed medium risks and mobility for aquatic biota. To mitigate heavy metal contamination, it is recommended to improve monitoring and regulation of urban runoff and inlet areas.

Mitigation of arsenic and zinc toxicity in municipal sewage sludge through co-pyrolysis with zero-valent iron: A promising approach for toxicity reduction of sewage sludge

Abstract The co-pyrolysis (at 300°C and 600°C) of municipal sewage sludge (SS) with zero-valent iron (Fe0: 1.5% and 3%) was investigated to reduce the toxicity of arsenic (As) and zinc (Zn) in SS. The BCR sequential extraction method, desorption kinetic analysis, and material characterization techniques (Fourier transform infrared spectroscopy, field-emission scanning electron microscopy, X-ray diffraction) were used to evaluate the effects of the treatments on Zn and As behavior. The results showed that co-pyrolysis significantly reduced the acid-soluble fraction (18–43% for Zn; 83–95% for As) and mobility factor (45–85% for Zn; 86–96% for As) of Zn and As compared to untreated SS. Desorption experiments indicated a significant reduction in Zn and As release in treated samples, particularly in the co-pyrolysis sample at 600°C and Fe0 3% (67% for Zn; 88% for As) in comparison with untreated SS. Co-pyrolysis of Fe0 and SS led to the formation of new functional groups (Si–O, aromatic), a more porous surface morphology, and highly stable chemical crystals (ferric arsenate, zinc arsenide), which played a crucial role in Zn and As stabilization. The findings of this study suggest that co-pyrolysis is a promising approach for mitigating As and Zn toxicity in SS. However, additional field testing with plant-based systems is necessary for confirmation.