Health and ecological risk assessment and simulation of heavy metal-contaminated soil of Tehran landfill

The toxic effects of heavy metals in landfill soils have become a significant concern for human health. The present study aimed to estimate the health and ecological risk associated with soil heavy metal in Tehran landfill. A total of 48 soil samples were taken from the landfill and residential area and were analyzed using inductively coupled plasma-optical emission spectroscopy. The results showed the following order for heavy metal levels in landfill soil: Al > Fe > Mn > Zn > Cr > Cu > Pb > Ni > Co > As > Cd. The investigated ecological indices showed moderate to high heavy metal pollution. The principal component analysis revealed that the concentration of Pb, Cu, Zn, Cr, and Ni in the investigated soil was mainly affected by anthropogenic activities. Although the hazard index (HI) value in children was 6.5 times greater than that of adults, this value for both landfill workers and residents of the target area was at a safe level (HI ≤ 1). In the residential area, the Incremental Lifetime Cancer Risk (ILCR) value of adults (1.4 × 10⁻⁴) was greater than children ILCR value (1.2 × 10⁻⁴). Monte Carlo simulation and sensitivity analysis showed input variables such as exposure duration, exposure frequency, Ni concentration, soil ingestion rate, and As concentration have a positive effect on ILCR of 41.3, 24.3, 9.4, 9.0, and 2.9% in children, respectively. These results indicate that the landfill soil and the adjacent residential area are affected by heavy metal contamination and that the current solid waste management policies need to be revised.

The toxic effects of heavy metals in landfill soils have become a significant concern for human health.     

Heavy metal pollution and human health risk assessment at mercury smelting sites in Wanshan district of Guizhou Province,China

The Wanshan district of Guizhou Province has a long history of mercury mining and smelting. Previous studies have been carried out on heavy metal (HM) pollution in the soil around Wanshan (such as in urban and farmland areas), but these studies have not been conducted at mercury smelting sites. In this study, the distribution characteristics of As, Be, Cd, Cr, Cu, Hg, Ni, Sb, Pb and Zn and their sources in the shallow stratum (<10 m) of the mercury smelting site in the Wanshan district were analyzed. Human health risks were evaluated using deterministic risk assessment (DRA) and probabilistic risk assessment (PRA) models. The contribution rates of different HM sources to human health risks were also calculated. The maximum HM concentration in mercury smelting site soil occured in the shallow soil (0–1 m), and the concentration sequences were as follows: 358.51 mg kg⁻¹ (Hg) > 248.6 mg kg⁻¹ (Zn) > 67.42 mg kg⁻¹ (As) > 59.04 mg kg⁻¹ (Ni) > 57.56 mg kg⁻¹ (Pb) > 49.59 mg kg⁻¹ (Cr) > 46.65 mg kg⁻¹ (Sb) > 15.65 mg kg⁻¹ (Cu) > 2.02 mg kg⁻¹ (Be) > 0.78 mg kg⁻¹ (Cd). The variable coefficients (CVs) were 1.64 (As), 0.67 (Be), 3.15 (Cd), 1.89 (Cr), 0.95 (Cu), 3.08 (Hg), 0.79 (Ni), 1.41 (Sb), 0.68 (Pb) and 1.13 (Zn), respectively. The HM concentrations in deep soils (9 m) still exceed the local background values, suggesting that heavy metals in shallow soil have migrated downward in the site. Three pollution sources identified with the shallow soil (0–1 m) HMs using the positive matrix factorization (PMF) model, were mercury smelting and coal combustion mixed sources (As, Hg and Zn), parent material sources (Ni, Cu, Cr, Cd and Sb) and wastewater discharge sources (Cu and Pb), respectively. DRA indicated that oral ingestion was the main pathway affecting the carcinogenic risk (CR) and hazard quotient (HQ) of heavy metals. The total-CR of twenty-five sampling points is between 1.219 × 10⁻⁶ and 3.446 × 10⁻⁴, and the total-HQ is between 0.37 and 43.56. PRA results indicated that DRA will underestimate the health risk of all populations in Guizhou Province, especially female, and BW_a is the most influential variable for the PRA results. Smelting and coal combustion mixed sources contributed the most CR (99.29%) and with an HQ of 89.38% were the major sources of pollution affecting human health.

The DRA model was used to analyze the human health risk contribute of different HMs sources in the mercury smelting site, and the PRA model was used to verify.     

Effects of amendments on the bioavailability,transformation and accumulation of heavy metals by pakchoi cabbage in a multi-element contaminated soil

This study aims to assess the effect of green waste compost (GWC), biochar (BC) and humic acid (HA) amendments of an alkaline heavy metal-contaminated soil. In this study, amendments with GWC, GWC + BC and GWC + HA were applied to the heavy metal-contaminated soil in four application rates (0, 1, 2 and 5%), and was aimed at substantially mitigating the bioavailability of heavy metals for pakchoi cabbage from the sewage irrigation soils. The addition of different ratios of amendments can increase the pH of the soil by 0.11–0.30 units and also increase the organic matter content by 3.1–35.1%. The concentration of available arsenic (As), cadmium (Cd), zinc (Zn) and copper (Cu) in the CaCl₂ extract was decreased effectively by all the amendments, except for the increase in the available concentration of As by compost–humic acid (T8) in the soil. Compared with the control, the CaCl₂ extractable Cd was decreased by 33–48% after the addition of different ratios of amendments in the soil. Moreover, by increasing the content of compost and compost–biochar in combinations, easily exchangeable fractions of As, Cd, Zn and Cu were decreased, while the oxidation fraction and residual fractions were increased. When the soil amendments were applied, fresh weight of the root and shoot increased by 29–63% and 39–85%, respectively. Cd concentration in the roots and shoots of the pakchoi cabbage decreased by 21–44% and 26–53%, respectively, after adding different ratios of amendments. All the amendments were effective in reducing the Cd, Zn and Cu uptake by the roots and shoots of the pakchoi cabbage, and simultaneously reduce the absorption of As in the roots of pakchoi cabbage. As soil amendments, GWC alone or GWC + BC/GWC + HA application can significantly reduce the heavy metal levels in pakchoi cabbage while increasing the biomass production and higher application rate is more effective than the lower application rate.

The concentration of available arsenic (As), cadmium (Cd), zinc (Zn) and copper (Cu) in CaCl₂ extract was effectively decreased by all the amendments, except the available concentration of As was increased by compost–humic acid (T8) in soil.     

Adsorption of cadmium by live and dead biomass of plant growth-promoting rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) have been extensively investigated in combination remediation with plants in heavy metal contaminated soil. However, being biosorbent, few studies of live and dead cells of PGPR have been undertaken. Meanwhile, the application of live or dead biomass for the removal of heavy metals continues to be debated. Therefore, this study uses living and non-living biosorbents of Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 to compare their Cd(ii) adsorption capacities by SEM-EDX, FTIR, and adsorption experiments. In the present study, whether the cells were living or dead and whatever the initial Cd(ii) concentration was, removal efficiency and adsorption capacity can be arranged as GX_31 > GX_15 > GX_5 (p < 0.05). However, removal efficiency in live and dead biosorbents was quite different and it greatly affected by the initial Cd(ii) concentrations. The dead cells exhibited a higher adsorption capacity than the live cells of GX_31. Nevertheless, for GX_5 and GX_15, the loading capacity of the non-living biomass was stronger than that of the living biomass at 20 mg L⁻¹ of Cd(ii), but the capacity was similar at 100 mg L⁻¹ of Cd(ii). Minor changes of spectra were found after autoclaving and it seemed that more functional groups of the dead biosorbent were involved in Cd(ii) binding by FTIR analysis, which also illustrated that the hydroxyl, amino, amide, and carboxyl groups played an important role in complexation with Cd(ii). Based on these findings, we concluded that the dead cells were more potent for Cd(ii) remediation, especially for GX_31.

Plant growth-promoting rhizobacteria (PGPR) have been extensively investigated in combination remediation with plants in heavy metal contaminated soil.     

Heavy metal accumulation and its spatial distribution in agricultural soils: evidence from Hunan province,China

The issue of heavy metal pollution in Hunan province, China, has attracted substantial attention. Current studies of heavy metal soil pollution in Hunan province mainly focus on medium and small scales, thus heavy metal pollution is rarely considered at the province scale in Hunan. In order to investigate the heavy metal pollution status in agricultural soils in Hunan province, literature related to heavy metal soil pollution in Hunan province was reviewed and organized from the following databases: Web of Science, China national knowledge infrastructure (CNKI), Wanfang Data, and China Science and Technology Journal Database (CQVIP). The literature data for the contents of Pb (122 soil sampling sites), Zn (103 sites), Cu (102 sites), Cd (105 sites), As (100 sites), Hg (85 sites), Cr (95 sites), and Ni (62 sites) in agricultural soils were obtained at the province scale. The spatial auto-correlation method was applied to reveal the spatial distribution of heavy metal accumulation. The average contents of the 8 heavy metals in agricultural soils of Hunan were all significantly (P < 0.05) higher than their background values and they were not distributed evenly across the Hunan province; the content of each heavy metal in eastern Hunan (including the cities of Yueyang, Changsha, Zhuzhou, and Chenzhou) was higher than that of other regions. The exceeding standard rate (the ratio of surveyed content to the background value) for Cu, Cd, As, and Hg had strongly positive spatial correlation, whereas Zn and Ni presented a negative spatial correlation. Overall, the higher exceeding standard rates of the 8 heavy metals were mainly distributed in the highly industrialized cities such as Changsha, Zhuzhou, Xiangtan, Chenzhou, and Hengyang, thus more attention should be paid to such areas to manage soil pollution.

Literature related to heavy metal soil pollution in Hunan province was reviewed and a spatial auto-correlation method applied to reveal the spatial distribution of heavy metal accumulation. The heavy metal content was highest in eastern Hunan.     

Bioremediation of cadmium-contaminated paddy soil using an autotrophic and heterotrophic mixture

Cadmium (Cd) pollution poses a serious risk to human health and ecological security. Bioremediation can be a promising and effective remediation technology for treating Cd contaminated soils. In this study, seven heterotrophic strains were isolated from Cd contaminated soil and 7 autotrophic strains were isolated from acid mine drainage. Cd removal efficiencies were compared after leaching with autotrophic bacteria (Att-sys), heterotrophic isolates (Htt-sys) and cooperative leaching systems (Co-sys) in laboratory agitating reactors. The results indicated that Cd removal efficiency of Co-sys (32.09%) was significantly higher than that of Att-sys (23.24%) and Htt-sys (0.74%). By analyzing the soil microbial community in different bioleaching systems, we found that the addition of heterotrophic isolates significantly promoted the growth of some heavy metal resistant inhabitants (Massilia, Alicyclobacillus, Micromonospora, etc.), and Co-sys had a minor effect on the growth of soil indigenous microbes. In Co-sys, the content of the four Cd fractions all decreased compared with other leaching systems. The analysis of soil physicochemical parameters during the leaching process showed that pH and ORP (oxidation reduction potential) were not the only determinants for Cd removal efficiency in Co-sys, synergistic metabolic activities of autotrophic and heterotrophic strains may be other determinants. This study demonstrated that cooperative bioremediation may prove to be a safe and efficient technique for field application in heavy metal soil pollution.

Bioremediation can be a promising and effective remediation technology for treating Cd contaminated soils. Cooperative bioremediation using heterotrophic and autotrophic mixtures proved to be an efficient, short-term bioremediation strategy for heavy metal contaminated soil.     

Cadmium isotope fractionation in the soil – cacao systems of Ecuador: a pilot field study

The often high Cd concentrations of cacao beans are a serious concern for producers in Latin America due to the implementation of stricter Cd limits for cocoa products by the European Union in 2019. This is the first investigation to employ coupled Cd isotope and concentration measurements to study soil – cacao systems. Analyses were carried out for 29 samples of soils, soil amendments and cacao tree organs from organic farms in Ecuador that harvest three distinct cacao cultivars. The majority of soils from 0–80 cm depth have very similar δ^114/110Cd of about −0.1‰ to 0‰. Two 0–5 cm topsoils, however, have high Cd concentrations coupled with heavy Cd isotope compositions of δ^114/110Cd ≈ 0.2%, possibly indicating Cd additions from the tree litter used as organic fertilizer. Whilst cacao leaves, pods and beans are ubiquitously enriched in Cd relative to soils there are distinct Cd isotope signatures. The leaves and pods are isotopically heavier than the soils, with similar Δ^114/110Cd_leaf–soil values of 0.22 ± 0.07‰ to 0.41 ± 0.09‰. In contrast, the data reveal differences in Δ^114/110Cd_bean–leaf that may be linked to distinct cacao cultivars. In detail, Δ^114/110Cd_bean–leaf values of −0.34‰ to −0.40‰ were obtained for Nacional cacao from two farms, whilst CCN-51 hybrid cacao from a third farm showed no fractionation within error (−0.08 ± 0.13‰). As such, further work to investigate whether Cd isotopes are indeed useful for tracing sources of Cd enrichments in soils and to inform genetic efforts to reduce the Cd burden of cocoa is indicated.

Cd isotope composition in cacao seems to be cultivar-specific whereas Cd in soil is probably due to tree litter recycling.     

Effects of an additive (hydroxyapatite–bentonite–biochar) on Cd and Pb stabilization and microbial community composition in contaminated vegetable soil

A two-year pot experiment was conducted with a pimiento–celery cabbage (Capsicum annuum L.–Brassica pekinensis) rotation in acidic soil contaminated with Cd and Pb, which was amended with 0.0, 1.0, 2.5, 5.0 and 10.0% (w/w) premixtures of hydroxyapatite, bentonite and biochar combinations (HTB, in a ratio of 1 : 2 : 2). The results showed that the application of HTB at 2.5–10.0% significantly increased soil pH and organic carbon by an average of 10.38–17.60% and 35.60–55.34% during the two years, respectively. Compared to the control treatment, 1.0–10.0% HTB decreased the available Cd and Pb concentrations by 40.92–77.53% and 41.60–82.79% on average, respectively. In addition, the diversity and richness of the soil bacterial community improved after the two-year application of HTB. The relative abundances of Acidobacteria, Bacteroidetes and Chloroflexi increased under the HTB treatments, while those of Proteobacteria and Actinobacteria decreased. Redundancy analysis (RDA) and regression analysis indicated that soil pH and Cd and Pb availability were important factors shaping the soil bacterial community. The Cd and Pb concentrations in the edible parts of pimiento and celery cabbage decreased as the HTB application rate increased and met the Food Quality Standard in each season when the HTB application rate was 5.0% or higher. Higher rates of HTB (5.0% and 10.0%) not only ensured the quality of vegetables, but also significantly promoted pimiento and celery cabbage growth. Overall, these results indicated that the application of HTB, especially at a rate of 5.0%, could be an effective way to immobilize Cd and Pb, improve soil quality and ensure vegetables produced in acidic contaminated soil are safe for human consumption.

A two-year pot experiment was conducted with an amendment of hydroxyapatite, bentonite and biochar combinations (HTB) to study the influence of HTB on soil physicochemical properties, soil Cd and Pb availability and microbial community composition.     

Reduction of Cd accumulation in pak choi (Brassica chinensis L.) in consecutive growing seasons using mercapto-grafted palygorskite

Cd contamination in agricultural fields poses a potential human health risk via food chain exposure. Proper remediation methods are critical to ensure the adequate safety of agricultural food products. In the current study, mercapto-grafted palygorskite (MP), a novel immobilization agent, was selected for the remediation of Cd-contaminated acid soils in pot experiments. Pak choi was used as the model plant. MP significantly reduced Cd accumulation in the shoots and roots of pak choi grown in Xiangtan and Guiyang soils in comparison to the control, in consecutive growing seasons, and the minimum Cd contents in shoots were less than the maximum permitted level proposed by the Codex Alimentarius Commission of FAO and WHO. Further, MP decreased the phytoavailable Cd content in soils determined using the diffusive gradient technique in thin-films in consecutive growing seasons with the maximum reductions of 86.26% and 89.51% respectively. These findings indicated that MP had a remarkable Cd immobilization efficiency in soils. MP had no obvious promotion impact on the pH value of either soil sample, but decreased the zeta potentials of both soil samples significantly, and then resulted in increases of the maximum sorption amounts of Cd of both soil samples. The results indicated MP could achieve remediation of Cd-contaminated soil by enhancing the sorption of Cd contaminants and the chemical sorption of Cd²⁺. The available sulfur content in both soils increased and soil enzyme activities, such as that of urease, were enhanced, thereby alleviating Cd-induced oxidation. These improvements of the index of soil environmental and biological qualities indicated that MP was environmentally friendly and compatible. The high performance of MP even at a small dosage suggested that when scaled up to agricultural operations over a large-area, MP had great potential to reduce Cd accumulation in vegetables, thereby ensuring the food safety of vegetables.

MP significantly reduced Cd accumulation in the shoots of pak choi in comparison to the control, in consecutive growing seasons, and the minimum Cd contents were less than the maximum permitted level proposed by the Codex Alimentarius Commission.     

Biosorption and bioaccumulation characteristics of cadmium by plant growth-promoting rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) not only promote growth and heavy metal uptake by plants but are promising biosorbents for heavy metals remediation. However, there exist arguments over whether extracellular adsorption (biosorption) or intracellular accumulation (bioaccumulation) play dominant roles in Cd(ii) adsorption. Therefore, three cadmium-resistant PGPR, Cupriavidus necator GX_5, Sphingomonas sp. GX_15, and Curtobacterium sp. GX_31 were used to study bioaccumulation and biosorption mechanisms under different initial Cd(ii) concentrations, using batch adsorption experiments, desorption experiments, scanning electron microscopy coupled with energy dispersive X-ray (SEM-EDX) spectroscopy, transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. In this study, with the increase of the initial Cd(ii) concentrations, the removal efficiency of strains decreased and the adsorption capacity improved. The highest Cd(ii) removal efficiency values were 25.05%, 53.88%, and 86.06% for GX_5, GX_15, and GX_31 with 20 mg l⁻¹ of Cd(ii), while the maximum adsorption capacity values were 7.97, 17.13, and 26.43 mg g⁻¹ of GX_5, GX_15, and GX_31 with 100 mg l⁻¹ of Cd(ii). Meanwhile, the removal efficiency and adsorption capacity could be ordered as GX_31 > GX_15 > GX_5. The dominant adsorption mechanism for GX_5 was bioaccumulation (50.66–60.38%), while the dominant mechanisms for GX_15 and GX_31 were biosorptions (60.29–64.89% and 75.93–79.45%, respectively). The bioaccumulation and biosorption mechanisms were verified by SEM-EDX, TEM and FTIR spectroscopy. These investigations could provide a more comprehensive understanding of metal-bacteria sorption reactions as well as practical application in remediation of heavy metals.

Plant growth-promoting rhizobacteria (PGPR) not only promote growth and heavy metal uptake by plants but are promising biosorbents for heavy metals remediation.     

Describing the toxicity and sources and the remediation technologies for mercury-contaminated soil

Mercury (Hg) is a natural element and its compounds are found as inorganic and organic forms in the environment. The different Hg forms (e.g., methylmercury (MeHg)), are responsible for many adverse health effects, such as neurological and cardiovascular effects. The main source of Hg is from natural release. Nevertheless, with the development of industrialization and urbanization, Hg-contaminated soil mainly influenced by human activities (especially near mercury mining areas) has become a problem. Therefore, much more attention has been paid to the development and selection of various treatment methods to remediate Hg-contaminated soils. This paper presented a systematical review of the recent developments for the remediation of Hg-contaminated soils. Firstly, we briefly introduced the Hg chemistry, toxicity and the main human activity-related sources of mercury in soil. Then the advances in remediation technologies for removing Hg pollution from the soil were summarized. Usually, the remediation technology includes physical, chemical and biological remediation technology. Depending on this, we further classified these remediation technologies into six techniques, including thermal desorption, electrokinetic extraction, soil washing, chemical stabilization, phytoremediation and microbial technology. Finally, we also discussed the challenges and future perspectives of remediating Hg-contaminated soils.

Mercury (Hg) is a natural element and its compounds are found as inorganic and organic forms in the environment.     

Accumulation risk and sources of heavy metals in supratidal wetlands along the west coast of the Bohai Sea

The heavy metals Al, Cr, Cu, Ni, Pb, Zn, Fe, Mn, As, and Cd in the rainfall-driven supratidal wetlands along the west coast of the Bohai Sea (the areas are named site 1, site 2, site 3, and site 4 from south to north in the gradient in this study) are tested for their accumulation risks and sources. Results show that the distribution and enrichment of the heavy metals in the supratidal wetlands are lower in site 1 than in sites 2–4. The risk indices (RIs) of all sites are less than 150, indicating low–moderate risk. However, the RI values are primarily dominated by the risk indices (E_rⁱ) of As and Cd. The accumulative contribution values of E_rⁱ-As and E_rⁱ-Cd in sites 1, 2, 3, and 4 are 79.05%, 77.80%, 80.54%, and 76.43%, respectively. Additionally, the contamination degree (C_d) and the Nemero comprehensive pollution index (PN) of the supratidal wetland in site 1 are 6.86 and 0.74 respectively, indicating a low-risk state. By contrast, the C_d and PN values of the other three supratidal wetlands are higher than those of site 1, suggesting an increasing accumulation risk for heavy metals in sites 2, 3 and 4. Our analysis indicates that the heavy metals Al, Cr, Mn, and Fe in all the supratidal wetlands mainly originate from the weathering of rocks and their parent materials. Pb is significantly correlated with anthropogenic activities, while Cu, As, and Cd are likely induced by anthropogenic activities and atmospheric deposition. The sources of Ni and Zn should be determined on the basis of the situation of the wetland and its surrounding areas. For example, Ni is mainly affected by anthropogenic activities in site 2, whereas the origins of Ni are soil parent materials or atmospheric depositions in sites 1, 3, and 4. Our results can provide data to support the utilization strategy and sustainable development plans for marine space resources on the coast of the Bohai Sea.

The accumulation risk and sources for heavy metals Al, Cr, Cu, Ni, Pb, Zn, Fe, Mn, As, and Cd were analysed in rainfall-driven supratidal wetlands.     

Platelet mitochondrial membrane depolarization reflects disease severity in patients with sepsis and correlates with clinical outcome

Introduction

Sepsis is still a leading cause of morbidity and mortality, even in modern times, and thrombocytopenia has been closely associated with unfavorable disease outcome. Decreases in mitochondrial membrane potential (depolarization) were found in different tissues during sepsis. Previous work suggests that mitochondrial dysfunction of platelets correlates with clinical disease activity in sepsis. However, platelet mitochondrial membrane potential (Mmp) has not been investigated in a clinical follow-up design and not with regard to disease outcome.

Methods

In this study, platelet mitochondrial membrane depolarization was assessed by means of a fluorescent Mmp-Index with flow cytometry in 26 patients with sepsis compared with control patients. Platelet Mmp-Index on admission was correlated with the clinical disease scores Acute Physiology and Chronic Health Evaluation Score II (APACHE II), Sequential Organ Failure Score (SOFA), and Simplified Acute Physiology Score II (SAPS II). Finally, platelet Mmp-Index on admission and follow-up were compared in the group of sepsis survivors and nonsurvivors. Expression of the prosurvival protein Bcl-xL in platelets was quantified by immunoblotting.

Results

Platelet mitochondrial membrane depolarization correlated significantly with the simultaneously assessed clinical disease severity by APACHE II (r = -0.867; P < 0.0001), SOFA (r = -0.857; P <0.0001), and SAPS II score (r = -0.839; P < 0.0001). Patients with severe sepsis showed a significant reduction in platelet Mmp-Index compared with sepsis without organ failure (0.18 (0.12 to 0.25) versus 0.79 (0.49 to 0.85), P < 0.0006) or with the control group (0.18 (0.12 to 0.25) versus 0.89 (0.68 to 1.00), P < 0.0001). Platelet Mmp-Index remained persistently low in sepsis nonsurvivors (0.269 (0.230 to 0.305)), whereas we observed recovery of platelet Mmp-Index in the survivor group (0.9 (0.713 to 1.017)). Furthermore, the level of prosurvival protein Bcl-xL decreased in platelets during severe sepsis.

Conclusion

In this study, we demonstrated that mitochondrial membrane depolarization in platelets correlates with clinical disease severity in patients with sepsis during the disease course and may be a valuable adjunct parameter to aid in the assessment of disease severity, risk stratification, and clinical outcome.     

Hectogram-scale green synthesis of hierarchical 4A zeolite@CuOx(OH)(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures with Superb Congo red adsorption performance

Delicate design of hierarchical nanoarchitectures has become a highly effective strategy to develop novel adsorbents with improved adsorption capacity. Herein, hectogram-scale green fabrication of hierarchical 4A zeolite@CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures (4A-Cu-T, T was the calcination temperature) with terrific Congo red (CR) dye adsorption performance was achieved through a simple, template-free and surfactant-free hydrothermal approach. A series of characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction and photoelectron spectroscopy demonstrated that all resultant adsorbents featured a core–shell structure with 4A zeolite as core ingredients and CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies as shell components. The adsorption experimental results pointed out that 4A-Cu-300 with a maximum adsorption capacity of 512.987 mg g⁻¹ showed the best adsorption performance amongst all as-prepared adsorbents, and the adsorption capacity of shell component-CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies was calculated up to 3685.500 mg g⁻¹. The shell thickness and phase ratio of CuO and Cu(OH)₂ in CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies played key roles in improving the adsorption capacity. The successive tests suggested that the “carbon deposition” resulted in the decreased adsorption capacity of first-regenerated adsorbents, but little variance in adsorption performance among regenerated samples demonstrated the good stability of such adsorbents. This work unlocks a method for the rational design of high-performance adsorbents via delicate decoration of poor-performance materials with nanosheet assemblies, which will endow the non-active materials with enhanced adsorption properties.

The growth of CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies on the surface of 4A zeolite transforms poor-performance 4A zeolite adsorbents into high-performance 4A-Cu-300 adsorbents for Congo red study.     

Adsorption of nitrification inhibitor nitrapyrin by humic acid and fulvic acid in black soil: characteristics and mechanism

The compound nitrapyrin is easily adsorbed by soil organic matter in high-organic matter soils, and this results in its effectiveness reducing significantly. In this study, the adsorption characteristics and mechanisms of nitrapyrin as an adsorptive on humic acid (HA) and fulvic acid (FA) as adsorbents were investigated. The results showed that the kinetics of adsorption of nitrapyrin on both HA and FA followed pseudo-second-order kinetic models (R² ≥ 0.925, P < 0.05) and the adsorption process included an initial fast-adsorption stage and a slow-adsorption stage thereafter. The adsorption efficiencies of nitrapyrin on HA + FA were higher than that on HA or FA alone, and that of HA was higher than that of FA. The adsorption isotherms of nitrapyrin on HA and FA could be optimally fitted with the Langmuir equation (R² ≥ 0.982, P < 0.05). The maximum adsorption capacities of nitrapyrin on HA, FA and HA + FA were 4896.49, 3173.70 and 4925.56 mg kg⁻¹, respectively. Synergistic adsorption of nitrapyrin in co-existing systems of HA and FA was also observed. The adsorption mechanism of nitrapyrin on both HA and FA involved hydrogen bonding and hydrophobic interaction. Therefore, HA and FA in the soil environment can adsorb a large amount of nitrapyrin and reduce its effectiveness, and they have a positive synergistic effect.

The compound nitrapyrin is easily adsorbed by soil organic matter in high-organic matter soils, and this results in its effectiveness reducing significantly.     

Effect of different forms of N fertilizers on the hyperaccumulator Solanum nigrum L. and maize in intercropping mode under Cd stress

In the present study, we investigated the effects of different forms of nitrogen fertilizers on the hyperaccumulator Solanum nigrum L. and maize in intercropping mode under cadmium (Cd) stress and explored the physiological response mechanism. This research lays the foundation for the appropriate use of nitrogen (N) fertilizer, reduced costs of ecological restoration, and phytoremediation of environmental pollution by using this intercropping system. The main greenhouse pot experiment was conducted using 1.92 mg kg⁻¹ Cd-contaminated soil. NH₄⁺–N fertilizer and NO₃⁻–N fertilizer treatments were performed along with no nitrogen fertilizer treatment as the control. The results indicate that intercropping could decrease the Cd uptake of maize compared with maize monocropping, but the biomass of maize would decrease under the intercropping mode. The application of N fertilizer to the maize–S. nigrum intercropping system could increase the total biomass of maize and S. nigrum. Compared with the NO₃⁻–N fertilizer treatment, the Cd content of stem, leaf and grain tissues of S. nigrum significantly increased by 9.43%, 22.2%, and 8.33%, respectively, under the NH₄⁺–N fertilizer treatment. The bioconcentration and translocation factors of S. nigrum significantly increased by 11.1% and 15.3%. Moreover, the Cd content of stem, leaf, and grain tissues of maize decreased by 26.5%, 21.2%, and 21.4%, respectively. The bioconcentration and translocation factors of maize significantly decreased by 38.8% and 46.7%. The application of N fertilizers promoted the accumulation of Cd in maize roots, while Cd content decreased in maize shoots. Compared with NO₃⁻–N fertilizer, NH₄⁺–N fertilizer can improve Cd accumulation in various S. nigrum tissues under intercropping, which could reduce Cd accumulation in maize under intercropping. Therefore, the application of NH₄⁺–N fertilizer is recommended for satisfactory bioremediation when using the Cd-hyperaccumulator S. nigrum and for supporting the safe production of maize in Cd-contaminated soil, thus enabling the goal of simultaneous agricultural production and remediation.

In the present study, we investigated the effects of different forms of nitrogen fertilizers on the hyperaccumulator Solanum nigrum L. and maize in intercropping mode under cadmium (Cd) stress and explored the physiological response mechanism.     

Distribution,contents and health risk assessment of heavy metal(loid)s in fish from different water bodies in Northeast China

This study aimed at investigating the accumulation and potential risks of eight metal(loid)s in fish from natural and culturing water samples in Northeast China. Chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), cadmium (Cd), lead (Pb) and mercury (Hg) contents in 16 fish species (155 samples) and sediments of their habitats were analyzed. In general, the concentrations of these eight metal(loid)s in most fish samples are lower than the guideline levels and legal limits, and the Pb and Hg level in 0.65% of samples were exceeded the quality standards in China. The Cr, As, Cd and Pb levels in most fish samples are less than those reported in previous studies. Nonetheless, Hg levels in these fish samples are significantly higher than those reported in previous studies conducted in other regions. Different from the wild fish, significant positive correlations are found between Cr, Ni, As and Cd concentrations in cultured fish and those in pond sediment (P < 0.05), which might be due to the closed static water environment and concentrated feeding operations. Cu, Zn, As and Hg concentrations differed significantly among wild species, while Cu and Zn concentrations differed significantly among cultured species (P < 0.05), which might be because of the different feeding and foraging habitats. The target hazard quotients (THQs) at high exposure levels of target metal(loid)s in the studied fish were below 1 (except for Hg), and the carcinogenic risk indices of Cr, As, and Cd were less than 10⁻⁴. The levels of metal(loid)s (except for Hg) in the studied fishes fell within an acceptable range, but more attention should be paid to the potential carcinogenic risks.

This study aimed at investigating the accumulation and potential risks of eight metal(loid)s in fish from natural and culturing water samples in Northeast China.     

Soft synthesis and characterization of goethite-based nanocomposites as promising cyclooctene oxidation catalysts

Goethite based nanocomposites with a different composition such as 6FeO(OH)·MnO(OH)·0.5H₂O (Mn-composite), xFeO(OH)·M(OH)₂·yH₂O (Co-composite (M: Co, x = 12, y = 3), Ni-composite (M: Ni, x = 7, y = 2)) and xFeO(OH)·MO·yH₂O (Cu-composite (M: Cu, x = 5.5, y = 3), Zn-composite (M: Zn, x = 6, y = 1.5)) have been prepared by a soft chemical synthesis consisting in acetate hydrolysis. The data provided by Fourier transform infrared (FTIR), ultraviolet-visible-near infrared (UV-Vis-NIR), electron paramagnetic resonance (EPR) and Mössbauer spectra account for a slight modification of all composites'' physicochemical properties compared to the starting material. Powder X-ray diffraction and transmission electron microscopy (TEM) investigations revealed the secondary phase nature and presence along with that of goethite. The TEM data are also consistent with a nano rod-like morphology with a 5–10 nm width and an average length of 40 nm. The catalytic oxidation of cyclooctene with O₂ using isobutyraldehyde as reductant and acetonitrile as a solvent was performed in batch conditions for 5 h at room temperature. The selectivity for the epoxide was higher than 99% for all tested solids. The conversion of cyclooctene decreased from 55% to 4% following the same order of variance as the base/acid sites ratio: Mn-composite > Fe-composite > Co-composite > Ni-composite > Zn-composite > Cu-composite. The 6FeO(OH)·MnO(OH)·0.5H₂O (Mn-composite) exhibited the most promising catalytic activity in cyclooctene oxidation, which can be correlated with the redox ability of Mn(iii) combined with the increased base character of this solid. The catalytic activity of this sample decreases by 10% after several successive reaction cycles.

Goethite based nanocomposites with different compositions (6FeO(OH)·MnO(OH)·0.5H₂O, xFeO(OH)·M(OH)₂·yH₂O or xFeO(OH)·MO·yH₂O where M = Co, Ni, Cu or Zn) have been prepared by a soft chemical synthesis via acetate hydrolysis.     

In situ electrochemical investigation of the reaction progress between Zr and a CuCl–SnCl2 mixture in a LiCl–KCl molten salt

The electrochemical behaviors of CuCl, SnCl₂ and a CuCl–SnCl₂ mixture were investigated by cyclic voltammetry (CV) and square wave voltammetry (SWV). The reduction potentials of Cu(i) and Sn(ii) on CV curves are −0.49 and −0.36 V, respectively, while the reduction potentials of Cu(i)–Sn(ii) in the CuCl–SnCl₂ mixture almost overlap. The co-chlorination reaction progress between CuCl–SnCl₂ and Zr was also studied by monitoring the concentration changes of Cu(i), Sn(ii) and Zr(iv) ions in situ by CV, SWV and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses. The results indicate that during the reaction, the concentration of Zr(iv) ions increases gradually, while those of Cu(i) and Sn(ii) decrease rapidly until they disappear. When the molar ratios of Cu(i) to Sn(ii) are 1 : 1 and 1 : 0.5, the reaction between Cu(i) and Zr is faster but cannot exceed twice that of Sn(ii) and Zr in a short time. When the theoretical product of ZrCl₄ is a constant, and with the proportion of CuCl to SnCl₂ decreasing from 1 : 0 to 0 : 1, the chlorination reaction time periods increase from 40 to 170 min. Chloride products such as Cu_xSn_y, Sn_xZr_y, and Cu_xZr_y, are formed with different molar ratios. The coupling effect caused by the formation of alloys will promote the chlorination reaction when the ratios of CuCl to SnCl₂ are 0.66 : 0.17 and 0.5 : 0.25. The results provide a theoretical basis for the electrolytic refinement of zirconium.

A LiCl–KCl–ZrCl₄ melt was prepared via a co-chlorination reaction between a binary mixture of CuCl–SnCl₂ and Zr, and the reaction progress was electrochemically monitored.