Re-yellowing of chromium-contaminated soil after reduction-based remediation: Effects and mechanisms of extreme natural conditions.

Chromium (VI) in soil poses a significant threat to the environment and human health. Despite efforts to remediate Cr contaminated soil (Cr-soil), instances of re-yellowing have been observed over time. To understand the causes of re-yellowing as well as the influence of overdosed chemical reductant in remediating Cr-soil, experiments on excess reducing agent interference and soil re-yellowing mechanisms under different extreme conditions were conducted. The results show that the USEPA method 3060A & 7196A combined with K2S2O8 oxidation is an effective approach to eliminate interference from excess FeSO4 reducing agents. The main causes of re-yellowing include the failure of reducing agents, disruption of soil lattice, and interactions between manganese oxides and microorganisms. Under various extreme conditions simulated across the four seasons, high temperature and drought significantly accelerated the failure of reducing agents, resulting in the poorest remediation effectiveness for Cr-soil (91.75 %). Dry-wet cycles promoted the formation of soil aggregates, negatively affecting Cr(VI) removal. While these extreme conditions caused relatively mild re-yellowing (9.46 %-16.79 %) due to minimal soil lattice damage, the potential risk of re-yellowing increases with the failure of reducing agents and the release of Cr(VI) within the lattice. Prolonged exposure to acid rain leaching and freeze-thaw cycles disrupted soil structure, leading to substantial leaching and reduction of insoluble Cr, resulting in optimal remediation effectiveness (94.37 %-97.73 %). As reducing agents gradually and the involvement of the water medium, significant re-yellowing occurred in the remediated soil (51.52 %). Mn(II) in soil enriched relevant microorganisms, and the Mn(IV)-mediated biological oxidation process was also one of the reasons for soil re-yellowing.

Ball-milled sulfide iron-copper bimetals based composite permeable materials for Cr (VI) removal: Effects of preparation parameters and kinetics study.

Zero-valent iron (ZVI) and modified ZVI have been investigated extensively for groundwater remediation. However, ZVI based powder was difficult to be applied directly as permeable reactive barrier (PRB) materials due to their low water permeability and usage rate. In this study, sulfide iron-copper bimetal was prepared by ball milling, which is environment-friendly without second contamination. The optimal preparation parameters of sulfide iron-copper bimetal for Cr(VI) removal were determined (Cu/Fe ratio (w/w), 0.018; FeS/Fe ratio (w/w), 0.1213; ball milling speed, 450 rpm; ball milling time, 5 h). A composite permeable material was prepared by sintering a mixture of sulfide iron-copper bimetal, sludge, and kaolin. The parameters for composite permeable material preparation including sludge content and particle size, and sintering time were optimized, which were 60%, 60-75 mesh, and 4 h, respectively. The optimal composite permeable material was characterized by SEM-EDS, XRD, and FTIR. The results demonstrated preparation parameters can affect the hydraulic conductivity and hardness of composite permeable material. High sludge content, small particles size, and moderate sintering time resulted in high permeability of composite permeable material and were beneficial for Cr(VI) removal. The dominant Cr(VI) removal mechanism was reduction, and the reaction followed pseudo-first order kinetics. Conversely, low sludge content and large particle size, and long sintering time lead to low permeability of composite permeable material. Chromate removal was mainly by chemisorption following pseudo-second order kinetics. The hydraulic conductivity and hardness of the optimal composite permeable material achieved 1.732 cm/s and 50, respectively. The results of column experiments indicated that its Cr(VI) removal capacity was 0.54 mg/g, 0.39 mg/g and 0.29 mg/g at pH 5, 7 and 9, respectively. The ratio of Cr(VI) to Cr(III) on composite permeable material surface was similar under acidic and alkaline conditions. This study will provide an effective reactive material of PRB for field application.

Remediation of Cr(VI)-contaminated soil mixed with chromite ore processing residue by ferrous sulfate and enzyme residue.

In this study, Cr(VI)-contaminated soil mixed with COPR by using ferrous sulfate (FeSO4), enzyme residue (ER), and their combination under aerobic or anaerobic condition were investigated. The concentration of Cr(VI) decreased from 1498.05 to 104.63 mg kg-1 after the simultaneous addition of FeSO4 (30 %, w/w as FeSO4·7H2O) and ER (30 %, w/w) at 45 d under the anaerobic condition with a reduction efficiency of 93.02 %, which is higher than that by single FeSO4 (72.39 %) or ER (75.47 %) under the anaerobic condition. XRD, XPS, FTIR, and fluorescence spectroscopy were conducted to characterize soil and ER composition. Metagenomic analysis was performed to reveal the reduction mechanisms of FeSO4 and ER. The anaerobic condition with lower Eh was beneficial for Cr(VI) reduction than aerobic condition, and Eh was the main driver for the evolution of Cr(VI) reduction-related microorganisms. Moreover, the addition of ER enriched the organic matter and microbials in the soil. During the decomposition of organic matter under the anaerobic condition, organic acids were generated, leading to a decrease in pH and promoting the release of Cr(VI) from minerals. They also served as electron donors in Cr(VI) reduction. Additionally, the addition of excess FeSO4 stimulated the growth of iron-reducing bacteria and sulfate-reducing bacteria, facilitating to Cr(VI) reduction. Metagenomic analysis showed that Acinetobacter, related to the nemA and nfsA genes, was the dominant Cr(VI) reduction genus. Thus, the combination of FeSO4 and ER is a promising method for the remediation of Cr(VI)-contaminated soils mixed with COPR.

Understanding and eliminating the reductant interference on Chromium VI measurement with USEPA method 3060A.

Excessive reductants are used in engineering to ensure a reliable remediation effect of chromite ore processing residue (COPR), however, re-yellowing phenomenon of remediated COPR occurs after some time though the Cr(VI) content meets regulatory requirements after curing period. This problem is due to a negative bias on Cr(VI) determination using USEPA method 3060A. To address this issue, this study tried to reveal the interference mechanisms and proposed two methods to amend the bias. Results of ion concentrations, UV-Vis spectrum, XRD, and XPS together showed that Cr(VI) was reduced by ions (Fe2+, S52-) in the digestion stage of USEPA method 3060A, and as a result, method 7196A would not reflect the true Cr(VI) concentration. The interference on Cr(VI) determination generated by excess reductants mainly occurs during the curing period of remediated COPR, but it decreases over time as reductants being oxidized gradually by the air. Compared with the thermal oxidation, the chemical oxidation with K2S2O8 prior to alkaline digestion performs better to eliminate the masking effect brought by excess reductants. This study provides an approach on how to accurately determine the Cr(VI) concentration in the remediated COPR. It might be helpful to reduce the occurrence possibility of re-yellowing phenomenon.

Insights into the evolution of Cr(VI) species in long-term hexavalent chromium contaminated soil.

Compare to the content of Cr(VI), the distribution of specific Cr(VI) species in soil is rarely paid attention to, which may lead to an inaccurate environmental risk assessment of Cr(VI) contaminated soil or inability to meet stringent requirement for soil remediation. Herein, to reveal the primary mechanisms and factors controlling the evolution of Cr(VI) species in soil, the distribution of Cr(VI) and Cr(III) species in soils with different particle sizes and textures was systematically investigated by using a modified sequential extraction procedure and spectroscopy characterizations (e.g., SEM-EDS mapping). The results show that a significant proportion of Cr(VI) can be captured by minerals containing exchangeable calcium ions and metal oxide hydrates in the soil, forming a relatively stable adsorbed Cr(VI). Also, a small fraction of Cr(VI) can precipitate as calcium chromate with free calcium ion which is the most stable Cr(VI) species in the soil. The majority of Cr(VI) discharged into soil tends to be reduced by ferrous ions or minerals containing ferrous ions with a product of Fe(III)-Cr(III) coprecipitate. Therefore, the speciation of Cr in the soil is closely correlated to Fe and Ca. After the equilibrium of adsorption, precipitation, and reduction reactions of Cr(VI), the rest of Cr(VI) retains as the form of its original water-soluble state in soil. The evolution of Cr(VI) species and the content of specific Cr species in soil are mainly determined by the contents of iron, exchangeable calcium ions and metal oxide hydrates, which effect the Cr(VI) reduction, precipitation and adsorption, respectively.

Factors Affecting the Detection of Hexavalent Chromium in Cr-Contaminated Soil.

The alkali digestion pretreatment method in the United States Environmental Protection Agency (USEPA) Method 3060A could underestimate the content of Cr(VI) in Cr-contaminated soils, especially for soils mixed with chromite ore processing residue (COPR), which leads to a misjudgment of the Cr(VI) level in soils after remediation, causing secondary pollution to the environment. In this study, a new pretreatment method to analyze Cr(VI) concentration in contaminated soils was established. The impacts of soil quality, particle size, alkali digestion time and the rounds of alkali digestion on Cr(VI) detection in contaminated soils was explored and the alkali digestion method was optimized. Compared with USEPA Method 3060A, the alkaline digestion time was prolonged to 6 h and multiple alkali digestion was employed until the amount of Cr(VI) in the last extraction was less than 10% of the total amount of Cr(VI). Because Cr(VI) in COPR is usually embedded in the mineral phase structure, the hydration products were dissolved and Cr(VI) was released gradually during the alkaline digestion process. The amount of Cr(VI) detected showed high correlation coefficients with the percentage of F1 (mild acid-soluble fraction), F2 (reducible fraction) and F4 (residual fraction). The Cr(VI) contents detected by the new alkaline digestion method and USEPA Method 3060A showed significant differences for soil samples mixed with COPR due to their high percentage of residual fraction. This new pretreatment method could quantify more than 90% of Cr(VI) in Cr-contaminated soils, especially those mixed with COPR, which proved to be a promising method for Cr(VI) analysis in soils, before and after remediation.

Flocculation inspired combination of layered double hydroxides and fulvic acid to form a novel composite adsorbent for the simultaneous adsorption of anionic dye and heavy metals.

Currently, simultaneous removal of anionic and cationic pollutants from combined pollution wastewater is a challenging subject. Here, a novel composite adsorbent which can simultaneously adsorb anionic azo dye and heavy metal cations was developed by flocculation inspired assembly of Mg2Al layered double hydroxides (LDH) and fulvic acid (FA). The results show that the negatively charged macromolecule FA is firmly intertwined with the positively charged LDH through electrostatic attraction and adsorption bridging. This composite adsorbent (Mg2Al LDH-FA) can effectively capture anionic Orange II by anion exchange adsorption derived from LDH component with the maximum adsorption capacity of 604 mg/g. Mg2Al LDH-FA also exhibits good adsorption performance for heavy metals due to the complexation with FA and surface precipitation on LDH. The adsorption isotherms of heavy metals coincided with Langmuir model or Freundlich model, and the adsorption capacities for Pb2+, Cu2+, Ni2+, Cd2+ could reach up to 661.5 mg/g, 116.3 mg/g, 117.3 mg/g, 235.2 mg/g respectively. Particularly, Mg2Al LDH-FA can simultaneously uptake Orange II and heavy metals from the stimulated combined pollution wastewater, moreover it shows higher adsorption capacity for each pollutant than that in the single pollutant case as the result of the synergistic adsorption effect between LDH and FA.

Removal and recycling of hexavalent chromium from alkaline wastewater via a new ferrite process to produce the valuable chromium ferrite.

Current technologies for removal of Cr(VI) are generally fit for acidic wastewater. In this study, a new ferrite process for removal and recycling of Cr(VI) from alkaline wastewater to produce the valuable chromium ferrite has been developed. The results show that this new ferrite method is a one-step process which can be divided into two successive reactions including Cr(VI) reduction to form coprecipitation (Cr0.25Fe0.75(OH)3) and subsequently magnetic conversion of Cr0.25Fe0.75(OH)3 induced by Fe2+ under the same alkaline condition. The total Fe/Cr mole ratio of 5:1 is at least required for the chromium ferrite transformation. Increasing temperature and pH can enhance the interaction of Fe2+ with Cr0.25Fe0.75(OH)3 and further promote the formation of chromium ferrite, while suppressing the generation of nonmagnetic by-product goethite. Almost pure chromium ferrite is formed under proposed optimum conditions (Fe/Cr = 7:1, 65 °C and pH of 9) with Cr(VI) removal ratio around 100%. The Cr(VI) remained in the filtrate can be reduced to 0.01 mg/L which is much lower than the limits concentration for surface water (≤0.05 mg/L). The chromium ferrite product whose molecular formula can be expressed as Cr0.5-xFe2.5+xO4 (where 0 ≤ x < 0.5) presents good magnetic properties and has the potential to be recycled as a useful material.

Microbial reduction of Cr(VI) in the presence of Ni, Cu and Zn by bacterial consortium enriched from an electroplating contaminated site.

The bioremediation of Cr(VI) has been intensively reported in recent years, while little information about Cr(VI)-reducing consortium enriched from in-situ contaminated soil has been revealed, specifically the functional genes involved. In this study, we verified a Cr(VI) reduction process by a consortium enriched from in-situ contaminated soil through enzymatic analysis. The chromate reductase gene ChrR has been successfully amplified and further analyzed, provided solid evidence to prove the Cr(VI) bio-reduction was an enzyme-mediated process. Meanwhile, the analysis of metabolic pathways demonstrates that the consortium could detoxicate and resist Cr(VI) and co-existing metals (Ni2+, Zn2+ and Cu2+) through membrane transport and DNA repair process. The co-existing heavy metals Zn and Cu had a relatively significant negative and positive effects on Cr(VI) reduction respectively, which may play important roles in the Cr(VI) contaminated soil bioremediation.

Improved performance and applicability of copper-iron bimetal by sulfidation for Cr(VI) removal.

The reactivity of zero-valent iron (ZVI) for the Cr(VI) removal in groundwater is mainly limited by the formation of a passivation layer during its application in permeable reactive barrier (PRB). A kind of sulfidated copper-iron bimetal (S-ZVICu) with high reactivity for Cr(VI) removal was prepared by depositing FeSx onto copper modified ZVI via a one-pot method. The surface characteristic, reactivity and Cr(VI) removal performance of S-ZVICu were investigated. It was found that S-ZVICu had a Cr(VI) removal capacity as high as 67.5 mg/g and little risk of secondary contaminant of Cu(II). The optimal Cu/Fe mass ratio and S/Fe molar ratio were 0.0125 and 0.084, respectively. The S-ZVICu exhibited great superiority of Cr(VI) removal compared with ZVI, sulfidated ZVI (SZVI) and coper-iron bimetal (ZVICu). Mineralogy and morphology analysis showed that S-ZVICu had a hierarchical structure of Fe0/Cu0/FeSx, which could effectively reduce the risk of secondary contaminant of copper ions. The mechanism analysis suggested that the copper and FeSx successively plated on the surface of ZVI played a dual role in promoting the corrosion of zero-valent iron, and was facilitated to electron transfer between Fe0, Cu0, FeSx and Cr(VI). In addition, the loose FeSx layer had a positive effect on alleviating the oxidation of ZVI in air, which was helpful in maintaining the reactivity of S-ZVICu in the air. S-ZVICu is an environmentally friendly material for sustainable and effective removal of Cr(VI) in groundwater.

[Preparation of Sulfidated Copper-Iron Bimetallic Composited Material and Its Mechanism for Chromium Removal].

Sulfidated copper-iron bimetallic particles (S-Fe-Cu) were prepared by sulfidation of copper-iron bimetallic particles (Fe-Cu) obtained by the replacement reaction in the liquid phase. The influencing factors of S-Fe-Cu in removing Cr(Ⅵ) in water were determined. BET, SEM-EDX, and XPS were used to analyze the superficial structure and mineralogy of S-Fe-Cu. Combined with batch experiments, the mechanisms of Cr removal were analyzed. The results showed that FeSx was successfully loaded on the surface of S-Fe-Cu, and the optimum S/Fe molar ratio and Cu/Fe mass ratio in theory were 0.056 and 0.025, respectively. Compared with Fe-Cu, the specific surface area of S-Fe-Cu increased by 2.1 times, and the Cr removal efficiency increased by 6.1 times under a pH of 5. A high Cr removal efficiency was maintained under alkaline conditions. Meanwhile, chloride ions could penetrate the passivation layer of iron-based material, which was beneficial to the direct oxidation of Fe0 to produce Fe(Ⅱ) and advance the performance of S-Fe-Cu for Cr removal. The XPS results showed that the removal mechanism of Cr(Ⅵ) in water included adsorption, reduction, and coprecipitation.

How the Soil Microbial Communities and Activities Respond to Long-Term Heavy Metal Contamination in Electroplating Contaminated Site.

The effects of long-term heavy metal contamination on the soil biological processes and soil microbial communities were investigated in a typical electroplating site in Zhangjiakou, China. It was found that the soil of the electroplating plant at Zhangjiakou were heavily polluted by Cr, Cr (VI), Ni, Cu, and Zn, with concentrations ranged from 112.8 to 9727.2, 0 to 1083.3, 15.6 to 58.4, 10.8 to 510.0 and 69.6 to 631.6 mg/kg, respectively. Soil urease and phosphatase activities were significantly inhibited by the heavy metal contamination, while the microbial biomass carbon content and the bacterial community richness were much lower compared to noncontaminated samples, suggesting that the long-term heavy metal contamination had a severe negative effect on soil microorganisms. Differently, soil dehydrogenase was promoted in the presence of Chromate compared to noncontaminated samples. This might be due to the enrichment of Sphingomonadaceae, which have been proven to be able to secrete dehydrogenase. The high-throughput sequencing of the 16S rRNA gene documented that Proteobacteria, Actinobacteria, and Chloroflexi were the dominant bacterial phyla in the contaminated soil. The Spearman correlation analysis showed the Methylobacillus, Muribaculaceae, and Sphingomonadaceae were able to tolerate high concentrations of Cr, Cr (VI), Cu, and Zn, indicating their potential in soil remediation.

[Effects of Chromium Pollution on Soil Bacterial Community Structure and Assembly Processes].

With the rapid development of industry, chromium (Cr) has become one of the main soil heavy metal pollutants in China, seriously affecting the soil ecological environment and health of residents. In this study, contaminated soil samples were taken around the tannery sludge yard area in Heibei Province. The Illumina MiSeq high-throughput sequencing technology was employed to analyze the structure and assembly processes of soil bacterial communities at different pollution levels. Results showed that chromium pollution significantly influences soil properties and soil bacterial communities. The composition and structure of bacterial communities were significantly shifted at different pollution levels. Furthermore, the α diversity of bacterial communities may decrease with relatively high concentrations of chromium. Bacterial communities in chromium polluted soil can be divided into 55 phyla, where Proteobacteria, Actinobacteria, Acidobacteria, Chloroflexi, and Firmicutes are the dominant phyla (relative abundance>5%). Moreover, the soil bacterial communities were dominated by the deterministic assembly process (homogeneous selection) and the stochastic ratios decreased with increases in the concentration of chromium in soil. The total concentration of chromium, soil moisture, pH, and organic matter were significantly correlated (P<0.05) with the bacterial communities. Therefore, these soil properties might be the driving factors affecting the structure of bacterial communities.

Processes of chromium (VI) migration and transformation in chromate production site: A case study from the middle of China.

The migration and redox transformation processes of toxic Cr(VI) in the upper and deep soil of chromate-polluted site are of great importance for the environmental risk control and soil remediation. In this study, soils from surface to deep (around 30-60 m) and the groundwater in a typical abandoned chromate production plant site which has experienced decades of contamination were both sampled and analyzed. The results show that the soil in the leaching workshop of Cr(VI), dichromate transformation workshop and chromium slag dumping ground exhibits severe contamination of chromium and the pollution has extended to the groundwater, causing serious pollution in groundwater too. The vertical migration and transformation of Cr(VI) in the soil layer are mainly affected by the soil permeability, organic matter content and the amount of water passing through the soil layer. During the downward migration, Cr(VI) tends to be retained by the clay layer and further accumulates around the depth of 5-10 m where the concentrations of both hexavalent and total Cr reach maximum values, and then continues to diffuse from the accumulation layer towards the deeper soil. Accompanying with the reduction of Cr(VI) by organic matter in the soil, the Cr(III) exists at various depths. When the depth is below the groundwater level of saturated aquifer, the distribution of chromium in the soil and groundwater reaches leaching and redox equilibrium due to the long-term interaction between the soil and groundwater.

The performance of emerging materials derived from waste organism blood and saponified modified orange peel for immobilization of available Cd in soil.

Waste organism blood (WOB) and orange peel are emerging stabilization materials obtained as by-products from agricultural processes, which are quite suitable for heavy metal immobilization in soil. In this work, waste organism blood and chemically modified orange peel (SOP) were investigated as potential sorbents for immobilization of available Cd in soil. Application of 5% WOB and SOP effectively immobilized cadmium (Cd) with an associated regulation of soil pH, among which the pH of acidic soil increased most significantly. While the application of 3% SOP alone stabilized almost the same amount of available Cd compared to WOB, it caused the highest stabilization rate of 58.85% when applied at 5%. By contrast, SOP combined with WOB (the mass ratio of the material is 1 : 1) at a 5% addition rate stabilized the available Cd in soils remarkably, with a stabilization rate of 57.74%. This study revealed that the soil particles after stabilization have a more compact and flaky structure, and the SOP and WOB had a particular pore structure, which was helpful for the adsorption of available Cd in soil. This study put forward new insights into the potential effects of Cd immobilization in contaminated soil by newly emerging stabilization biomass materials (WOB and SOP).

Bacterial communities and potential waterborne pathogens within the typical urban surface waters.

Waterborne pathogens have attracted a great deal of attention in the public health sector over the last several decades. However, little is known about the pathogenic microorganisms in urban water systems. In this study, the bacterial community structure of 16 typical surface waters in the city of Beijing were analyzed using Illumina MiSeq high-throughput sequencing based on 16S rRNA gene. The results showed that Bacteroidetes, Proteobacteria and Actinobacteria were the dominant groups in 16 surface water samples, and Betaproteobacteria, Alphaproteobacteria, Flavobacteriia, Sphingobacteriia and Actinobacteria were the most dominant classes. The dominant genus across all samples was Flavobacterium. In addition, fifteen genus level groups of potentialy pathogenic bacteria were detected within the 16 water samples, with Pseudomonas and Aeromonas the most frequently identified. Spearman correlation analysis demonstrated that richness estimators (OTUs and Chao1) were correlated with water temperature, nitrate and total nitrogen (p < 0.05), while ammonia-nitrogen and total nitrogen were significantly correlated with the percent of total potential pathogens (p ≤ 0.05). These results could provide insight into the ecological function and health risks of surface water bacterial communities during the process of urbanization.

Sorption of 17ß-estradiol to the dissolved organic matter from animal wastes: effects of composting and the role of fulvic acid-like aggregates.

Steroid estrogens, such as 17ß-estradiol (E2), in animal manure pose a potential threat to the aquatic environment. The transport and estrogenicity of estrogens influence the sorption of estrogens to dissolved organic matter (DOM) in animal manure, and composting treatment alters the structure and composition of the manure. The objectives of the present study were to identify the contribution of the molecular composition of DOM of composted manure to the sorption of E2 and then elucidate the dominant mechanisms involved in the interaction of E2 with manure-derived DOM. The excitation-emission matrix (EEM) spectra and atomic force microscopy (AFM) showed that composting significantly altered the chemical composition and structure of DOM. A decrease in the atomic ratios of oxygen (O)/carbon (C) occurred in conjunction with the formation of DOM aggregates in the composted manure, indicating that the hydrophilicity and polarity of the DOM decreased after composting. Composting increased the sorption coefficients (KDOC-E2) for E2 to DOM, and KDOC-E2 was positively correlated with the proportion of the fulvic acid (FA)-like fraction and molecular weight (MW) fractions of the DOM (range of 1.0 × 103-7.0 × 103 Da and 7.0 × 103-1.4 × 104 Da). Specifically, E2 showed a tendency for sorption to medium-sized FA-like molecules of DOM aggregates in composted manure. Hydrophobic forces and π-π binding appeared to be the main mechanisms underlying the aforementioned interaction.

Environmental risks of HBCDD from construction and demolition waste: a contemporary and future issue.

Hexabromocyclododecane (HBCDD), as one of the most widely used brominated flame retardants (BFRs), is of great concern globally because of its persistence in the environment and negative impacts on humans and animals. HBCDD has been mainly used in flame-retarded expanded (EPS) and extruded (XPS) polystyrene foams for insulation in the construction industry. Most of these products will become a part of the construction and demolition (C&D) waste at the end of their life cycle (30-50 years) which is typically disposed of into landfills or incineration. However, the recycling of this material takes quite a low share compared with landfill and incineration. Consequently, high environmental risks will exist in these disposal approaches due to the HBCDD in C&D waste. Currently, XPS or EPS products containing HBCDD in the construction industry have not reached the end of their life cycle in most countries. Relatively little attention has been paid to this emergency issue by either the government or public. Furthermore, C&D waste is most likely disposed of by direct dumping, simple stacking, or open burning in developing countries. Therefore, this paper highlights the global environmental risks of HBCDD from C&D waste. Areas of research for key problems of HBCDD contained in C&D waste are suggested to help control and finally eliminate the impact.

Passive air sampling for determining the levels of ambient PCDD/Fs and their seasonal and spatial variations and inhalation risk in Shanghai, China.

The seasonal and spatial variations, compositional profiles, and possible sources of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in ambient air samples in Shanghai of China were investigated by passive air samplers, and the potential inhalation risks posed by these chemicals were evaluated. The following results were obtained: (1) The World Health Organization (WHO) toxic equivalency (TEQ) values for PCDD/Fs were in the range of 10.8-259 fg m(-3) (mean 63.4 fg m(-3)) in summer and 24.1-154 fg m(-3) (mean 83.4 fg m(-3)) in winter. Atmospheric PCDD/F levels were in the following order: industrial areas > commercial and residential areas > rural areas. (2) 2,3,4,7,8-PeCDF (24 %), 2,3,7,8-TeCDD (16 %), 1,2,3,7,8-PeCDD (13 %), and 2,3,7,8-TeCDF (12 %) were the predominant contributors to the TEQ of PCDD/Fs. (3) There was a slight seasonal trend with higher TEQ values in winter than in summer, which could be related to seasonal variations in the dispersion of PCDD/Fs in ambient air. (4) The children's daily intake was at the lower end of the range for the tolerable daily intake of PCDD/Fs recommended by WHO, which indicates that the inhalation risk of PCDD/Fs for local residents in Shanghai is relatively low.

Mineral phases and release behaviors of as in the process of sintering residues containing as at high temperature.

To investigate the effect of sintering temperature and sintering time on arsenic volatility and arsenic leaching in the sinter, we carried out experimental works and studied the structural changes of mineral phases and microstructure observation of the sinter at different sintering temperatures. Raw materials were shaped under the pressure of 10 MPa and sintered at 1000~1350°C for 45 min with air flow rate of 2000 mL/min. The results showed that different sintering temperatures and different sintering times had little impact on the volatilization of arsenic, and the arsenic fixed rate remained above 90%; however, both factors greatly influenced the leaching concentration of arsenic. Considering the product's environmental safety, the best sintering temperature was 1200°C and the best sintering time was 45 min. When sintering temperature was lower than 1000°C, FeAsS was oxidized into calcium, aluminum, and iron arsenide, mainly Ca3(AsO4)2 and AlAsO4, and the arsenic leaching was high. When it increased to 1200°C, arsenic was surrounded by a glass matrix and became chemically bonded inside the matrix, which lead to significantly lower arsenic leaching.