Environmental risk presented by arsenic contamination of building and facility surfaces in a coking plant.

Arsenic contamination on the surface of buildings and facilities at a coking plant and associated health risk were studied. A total of 94 wipe samples from 56 buildings and facilities were collected, and As concentrations were found to range from 0.01 to 23.90 µg/100 cm(2). 20.2% of the samples exceeded the As level calculated to present health risk: 4.02 µg/100 cm(2). Arsenic mean concentration was found to be highest on the surface of bricks, and coking zone showing the highest As risk. The findings of this study may provide clues to As pollution control and risk evaluation in coking plants.

The Fe3O4-modified biochar reduces arsenic availability in soil and arsenic accumulation in indica rice (Oryza sativa L.).

Arsenic (As)-contaminated paddy soil could result in elevated levels of As in rice plants and sequentially harm human health. The Fe3O4-modified biochar (NBC-Fe) prepared by the coprecipitation method was applied in a pot experiment to investigate its effect on mobility and bioavailability of As in soil and to reduce As accumulation in rice tissues (brown rice, husks, spikelets, leaves, stems, and roots). Compared with non-application (CK), application of NBC-Fe significantly increased the cation exchange capacity (CEC), decreased As availability, and raised the As concentration of crystalline hydrous oxide-bound fraction in the soil. The addition of 0.05-1.6% (w/w) NBC-Fe significantly reduced the As concentrations in brown rice by 9.4-47.3%, which was lower than the level set by the National Food Safety Standards of China (0.2 mg/kg). The NBC-Fe treatment decreased As concentrations in iron plaque (DCB-As), and the DCB-As had the very significant correlations (P < 0.01) with the As concentrations in different rice tissues (brown rice, husks, spikelets, leaves, stems, and roots). The NBC-Fe immobilized As to decrease As availability in soil and increased the amount and thickness of iron plaque to sequester As on the surfaces of rice root. This study demonstrates that NBC-Fe is a promising soil amendment for the remediation of As-contaminated soil, therefore reducing As accumulation in rice plant and safety risks for rice consumption.

[Stabilizing Effects of Fe-Ce Oxide on Soil As(â ¤) and P].

The mining and smelting of arsenic-containing metal minerals, and the large-scale use of chemicals and pesticides, has resulted in the widespread pollution of soils in southwestern and southern China. In this study, the stabilizing effect of Fe-Ce oxide (FC) on three representative arsenic-contaminated soils was evaluated. The microscopic adsorption characteristics of FC and As(Ⅴ) were explored by scanning electron microscopy and energy disperse spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The results showed that FC can significantly reduce arsenic concentrations by 84.1%-98.3% during the Toxicity Characteristic Leaching Procedure (TCLP), and showed strong pH adaptability in alkaline soil. It efficiently transformed (non-)specifically sorbed arsenic (F1+F2) into hydrous oxides phases of Fe and Al (F3+F4). FC also significantly reduced available P by 47.13%-60.32% in different types of soil. FC can not only release As(Ⅴ) adsorption sites occupied by P in soils, but also effectively prevents non-point source pollution of the surrounding water. SEM-EDS and XPS analysis detected Fe, Ce, and As on the surface of As(Ⅴ) adsorption products, and As was mainly adsorbed on the surface of Fe atoms. The results of this study provide a scientific basis for soil arsenic stabilization in China.

[Mineral Characteristics of Arsenic in the Active Area of the Banbishan Gold Mine and Its Effect on Arsenic Accumulation in Farmland Soil].

To explore the source and pollution characteristics of soil arsenic, mineralogy and chemical analysis methods were used to analyze the ore, waste rock, sediment, and river and soil samples around the mining area. Under a polarized light microscope, As-bearing mineral-arsenopyrite was found in the soil, ore, and waste rock around the Banbishan gold mine. Moreover, arsenopyrite in the waste rock has already experienced weathering and oxidation, and the oxidized arsenopyrite easily migrates and is released in the soil, which is potentially harmful. Because of the effect of mining transportation activities and indigenous smelting, arsenic was mainly distributed in the topsoil, at a depth of 0-20 cm, in the farmland on both sides of the road and in the places where villagers were gathered. The soil arsenic content in Xiaowulan Village and Gaozhangzi Village ranged from 7.2 to 196.2 mg·kg-1 and exceeded the rate of arsenic by 45.9% and 82.1%. According to the assessment by the RAC method, the farmland soil in Xiaowulan Village and Gaozhangzi Village were mainly at low to medium risk, although some soil points in Xiaowulan Village were at high risk. In general, the effects of the mining activities of the surrounding environment were not optimistic. As-bearing minerals in the oxidation of long-term weathering can cause much arsenic to be activated, which in turn, affects the local crops and long-term residents living around the mining area. It is suggested to carry out risk assessments for arsenic in the soil-crop-atmospheric-human system, and further study the conversion rules and mechanisms of arsenopyrite during weathering, to provide scientific guidance for the environmental protection of cultivated land.

[Adsorption and Mechanism of Arsenic by Natural Iron-containing Minerals].

Natural iron-containing minerals present in the geosphere in the form of crystalline minerals can be used as adsorption material for removal of arsenic from wastewater and remediation of arsenic-contaminated soils. In this paper, the adsorption and desorption of arsenic onto different iron-containing materials including hematite, limonite, siderite, ilmenite, magnetite, Fe2O3, Fe3O4, and Fe-Mn binary oxide (FMBO) were studied in laboratory experiments. The mechanism of arsenic adsorption was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), and fourier transform infrared spectroscopy (FTIR). The results showed that arsenic adsorption is fitted by pseudo-second-order kinetics and the Langmuir isotherm model for almost all adsorbents, suggesting monolayer adsorption of arsenic onto the minerals. The sorption efficiency and capacity of arsenic by FMBO are much higher than those of other materials. Furthermore, limonite has high sorption efficiencies for both As(Ⅲ) and As(Ⅴ) among the natural iron-containing minerals, and their adsorption capacities are 3.96 mg·g-1 and 2.99 mg·g-1, respectively. The XRD results showed that natural limonite contains a large number of weak crystalline mineral components such as goethite, which can provide relatively abundant arsenic adsorption sites. Thus, limonite appears to be the most suitable natural mineral for arsenic adsorption.

In-situ solidification/stabilization of heavy metals contaminated site soil using a dry jet mixing method and new hydroxyapatite based binder.

In this study, in-situ treatment using dry jet mixing construction method and SPC (single superphosphate and calcium oxide) new binder are used to solidify/stabilize a heavy metal contaminated site soil with relatively high content of organic matters. Time-dependent field performance of the soils at 41 and 326 days after treatment is evaluated, which includes electrical conductivity (EC), leachability of heavy metals and chemical oxygen demand (COD), soil penetration resistance, acid neutralization capacity (ANC), and chemical speciation of heavy metals. The results indicate that the stabilized soils exhibit satisfactory performance which is comparable with the laboratory study. In-situ SPC treatment significantly decreases EC values and increases penetration resistance values of the soils. Leachability of lead, zinc, cadmium and COD decreases with increasing SPC content or curing time. Large percentages of heave metals in the soils are transformed from exchangeable fractions to residual fractions after treatment. These, coupled with the improved ANC, result in low heavy metal leachability in stabilized soils.

[Stabilization Effects of Fe-Mn Binary Oxide on Arsenic and Heavy Metal Co-contaminated Soils Under Different pH Conditions].

pH is one of the most important factors affecting speciation and stabilization of arsenic and heavy metals in soil. In this study, Fe-Mn binary oxide (FMBO), synthesized by redox and precipitation reactions, was taken as the research object to evaluate its stabilization effects on As, Pb, Cd, Zn, and Cu in three types of soils under different pH conditions and to study the impacts on soil pH and buffering capacity. The results showed that the leaching concentrations of As and Pb were lower in the pH range of 3-9 (neutral and weak acidic) and 5-10 (neutral and weak alkaline); and Cd, Zn, and Cu were stable in the pH range of 7-11 (alkaline). The stability and stabilization effects of FMBO were better under alkaline conditions than acidic. In the optimal pH range, the optimum stabilization efficiency of FMBO could reach 92.7%, 100%, 97.0%, 88.7%, and 82.7% for As, Pb, Cd, Zn, and Cu, respectively. In addition, FMBO addition could increase soil pH and the acid buffering capacity moderately, which improved heavy metal stabilization and made it more suitable for acid soils and areas with more acid rain. From the correlation of contaminants and soil elements in the leachates, Fe played an important role in As stabilization, and pH had a great influence on the stabilization of Pb, Cd, Zn, and Cu.

[Effects and Mechanisms of In-situ Cement Solidification/Stabilization on a Pb-, Zn-, and Cd-Contaminated Site at Baiyin, China].

In order to evaluate the effects and mechanism of in-situ cement solidification/stabilization (S/S) on heavy metal contaminated soils, leaching tests, speciation analysis, and microscopic analysis were conducted after cement treatment of a Pb, Zn, and Cd contaminated site in Baiyin, China. The leaching test results showed that cement could effectively stabilize Cd and Zn, which could reduce 99.5%-100% and 96.6%-98.8% of H2SO4-HNO3 extractable Cd and Zn, respectively. However, the leaching concentration of Pb was 2.6-5.8 times higher than that before 5% cement treatment. After adding 8% cement, H2SO4-HNO3 extractable Cd and Zn were reduced by 99.6%-100% and 94.4%-97.9% respectively. Similarly, the leaching concentration of Pb was 1.9-12.5 times higher than that before 8% cement treatment. The results of sequential extraction test proposed by the European Community Bureau of Reference (BCR) showed that cement could transform acid extractable Cd and Zn to residual form and transform reducible fractions of Pb to oxidizable and residual form, increasing the stability of heavy metals in soil. The microscopic analysis results showed that Pb2+, Zn2+, and Cd2+ could participate in the process of cement hydration and form silicate minerals and hydroxides. In conclusion, cement could be an effective S/S agent to remediate heavy metal contaminated soils, and site characteristics and environmental conditions should also be considered during the construction process.

[Influence of Arsenate and Phenanthrene on Carbon-groups of Pteris vittata L. Roots].

To ascertain absorption of arsenate and phenanthrene as well as their influence on carbon groups in excised roots of Pteris vittata L., the chemical structure of the carbon groups in excised roots was characterized by solid state13C-Nuclear Magnetic Resonance (13C-NMR). The results showed that the excised roots could effectively absorb As and PHE without transpiration, and PHE promoted As accumulation in the roots. Similarly, arsenate increased the adsorption of PHE by the excised roots, the concentration of PHE was increased by 15%-53% compared with CK. The carbon groups of the excised roots were dominated by O-alkyl C, the percentage of carboxyl C was the lowest, mainly composed of carboxylic acids, esters and amides. With the addition of As and PHE, the percentage of carboxyl C increased significantly. The more stable and complex aromatic organic matter was formed to improve the resistance and adaptability in excised roots of Pteris vittata L. under As and PHE stress.

[Occurrence Characteristics of Pyrene and Arsenate and Their Interaction in Pteris vittata L].

Pteris vittata L. can absorb and accumulate high arsenic levels in soil. To clarify the occurrence characteristics of pyrene (PYR) and arsenate (As) as well as their interaction in P. vittata L., the hosting and distribution rules of PYR were determined via two-photon laser scanning confocal microscopy (TPLSCM). The results showed that PYR addition resulted in obviously lower concentrations of total As in various parts of P. vittata, with a largest decrease of about 35% in the leaves and stem, and 20. 5% in the roots. PYR addition could also decrease the proportion of trivalent arsenic and increased that of pentavalent arsenate in different parts of P. vittata. The concentrations of trivalent and pentavalent arsenic in the leaves of P. vittata showed the largest decrement, which were 42.2% and 32.49%, respectively. Arsenate addition increased the accumulation of PYR in the root and stem of P. vittata by 9.8 µg and 139 ng per plant, respectively, while no obvious influence was found on the PYR in the leaves. Pyrene mainly attached to the cell membrane and other membrane structure such as nuclear membrane and organelle membrane, and there was less pyrene in the cytoplasm. There was little PYR in the phloem and cortex in the stem as well as palisade tissue and spongy tissue in leaves.

[Effects of Soil Moisture on Phytoremediation of As-Containinated Soils Using As-Hyperaccumulator Pteris vittata L].

A pot experiment was carried out to study the effects of soil moisture on the growth and arsenic uptake of As-hyperaccumulator Pteris vittata L. The results showed that the remediation efficiency of As was the highest when the soil moisture was between 35%-45%. P. vittata grew best under 45% water content, and its aboveground and underground plant dry weights were 2.95 g x plant(-1) and 11.95 g x plant(-1), respectively; the arsenic concentration in aboveground and roots was the highest under 35% water content, and 40% content was the best for accumulation of arsenic in P. vittata. Moreover, controlling the soil moisture to 35%-45% enhanced the conversion of As(V) to As(III) in aboveground plant, and promoted arsenic detoxification in P. vittata. These above results showed that soil moisture played an important role in the absorption and transport of arsenic by P. vittata. The results of this study can provide important guidance for the large-scale planting of P. vittata and the moisture management measures in engineering application.

[Discussion on several key points of decision support system for remediation of contaminated sites].

The problem of site contamination has become a focus in the environment protection field in the recent years. Decision support system (DSS) for remediation of contaminated sites is used for selecting the optimal remediation technologies and formulating economic and efficient remediation plans based on site investigation and risk assessment. This paper reviewed and analyzed the key steps in the decision-making process, including frames, models and methods. In addition, the modules and functions of more than 40 types of decision-making software in the world were evaluated and summarized. Aimed at the demand of site contamination in our country, a skeleton frame and feature were proposed in the paper, where the international experience in developed countries has been absorbed and learned.

[Effect of thermal enhanced soil vapor extraction on benzene removal in different soil textures].

Experiments were carried out to investigate the effect of thermal enhanced soil vapor extraction (SVE) on benzene removal from sand, loam and clay and the mechanism. Compared to the routine control treatment, the benzene removal rates were improved by 13. 1% and 12. 3% and the remediation periods were reduced by 75% and 14%, from sand and loam respectively using thermal enhanced SVE. Thermal enhancement decreased the moisture content and increased the soil permeability of clay. On the surface of clay particles, absorption peaks of carboxyl and ethyl disappeared and the content of soil organic substances decreased significantly. Compared to the conventional SVE, the benzene removal rate was improved by 34% in clay soil treated by thermal enhanced SVE. For sand and loam, thermal enhancement could increase the removal rate by promoting the diffusion of benzene in the soil and achieve substantial removal of pollutants in a relatively short period of time. For clay, it could enhance the effect of SVE by reducing the absorption capacity between soil particle surface and contaminant and improving the performance of the gas diffusion in soil by decreasing the moisture content and increasing the soil permeability.

[Urban industrial contaminated sites: a new issue in the field of environmental remediation in China].

Contamination of urban industrial lands is a new environmental problem in China during the process of upgrade of industrial structure and adjustment of urban layout. It restricts the safe re-use of urban land resources, and threatens the health of surrounding inhabitants. In the paper, the market potential of contaminated-site remediation was known through analysis of spatial distribution of urban industrial sites in China. Remediation technologies in the Occident which were suitable for urban industrial contaminated sites were discussed and compared to evaluate their superiority and inferiority. And then, some advices of remediation technologies for urban industrial contaminated sites in China were proposed.

[Pb pollution on surfaces in a typical coking plant and health risk assessment].

Pb pollution on the surfaces of buildings and devices at a coking plant was studied. The objectives of this study were to determine the Pb content and its spatial variation on the surfaces, and to assess the potential health risk from this Pb. Ninety-four wipe samples were collected from 56 buildings and devices at the coking plant, and their Pb contents were determined. Surface Pb concentrations ranged from 0-538 micro x g/dm2, and concentrations in 78.7% of the samples exceeded the US Department of Housing and Urban Development (HUD) standard (2.69 microg/dm2). By area, the proportion of samples with concentrations greater than the US HUD standard were 78.9% in the office and living zone, 75.0% in the refining zone, 73.7% in the coking zone and 78.6% in the coke-gas zone. Among the various types of surfaces, the coke pusher had the highest average surface concentration of Pb. The average surface concentrations of Ph on common coking plant surface materials followed the order paints > brick > cement > glass, and the concentrations in 94.4% of the wipe samples taken from paint surfaces exceeded the US HUD standard.

[Chemical oxidants for remediation of soils contaminated with polycyclic aromatic hydrocarbons at a coking site].

Different oxidants were evaluated for removal of polycyclic aromatic hydrocarbons (PAHs) from contaminated soils at industrial coking sites with the use of simulating device, and the fate of pollutants during the treatment was investigated. Permanganate showed the highest PAHs removal rate (96.2%) of the oxidants studied. Most of the PAHs were oxidized and only < 1% of PAHs volatilized and transferred to the solvent. The removal of PAHs by activated persulfate reached 92%. Modified Fenton reagent could remove 80% of PAHs, and < 2% of PAHs volatilized and transferred to the solvent after treatment with activated persulfate and modified Fenton reagent. The efficiencies of hydrogen dioxide and Fenton reagent for removal of PAHs were both < 60% ,and up to 6% of PAHs volatilized and transferred to the solvent. In summary, permanganate and activated persulfate are the most effective and environment-friendly oxidants for removing PAHs from contaminated soils. The chemical oxidants could easily remove ANY, ANT, BaP, DahA, BghiP and IcdP, but FLE, CHR and Fla were relatively resistant to chemical oxidation.

[Accumulation of soil arsenic by Panax notoginseng and its associated health risk].

Panax notoginseng is a valued traditional Chinese medical herb. In this study, the arsenic (As) contamination of soil in P. notoginseng plantation area in Wenshan (Yunnan, China) was investigated; the absorption and accumulation of soil As by the P. notoginseng was revealed; and the associated health risk was evaluated. The results revealed that the soil As concentrations ranged between 6.9-242.0 mg x kg(-1). Arsenic concentrations in 48% of the total soil samples were > 40 mg x kg(-1). The As concentrations in 24% of main root samples, 81% of fibrous root samples, 14% of stem samples, 57% of leaf samples, and 44% of flower/fruit samples were greater than the regulation concentration of 2.0 mg x kg(-1). Arsenic accumulation in the main root increased with the soil As concentration at soil As concentrations < 100 mg x kg(-1), but sharply decreased with the soil As concentration at soil As concentrations > 100 mg x kg(-1). With increasing soil As concentration, the total biomass of P. notoginseng and the main root biomass decreased. Calculating with the As concentration in different parts of Sanqi P. notoginseng plants, percent of the average ingestion rates of As with ADI regulated by FAO/WHO showed fibrous root > leave > flower/fruit > main root > stem. Based on the As concentration in the main root, the daily As intake accounted for a mean fraction of 12.83% (maximum 45.87%) of the acceptable daily intake specified by FAO/WHO,and the ratio increased with the increasing of soil As concentration. Arsenic contamination of soil and P. notoginseng at the plantation area of Wenshan should not be neglected, and effective strategies should be adopt to reduce As accumulation in the plant and human health risk.

[Comparative study on determinations of BTEX in soils from industrial contaminated sites].

In order to ascertain BTEX measurements of soils from industrial contaminated sites, static headspace, purge-and-trap and solid phase microextraction (SPME) combined gas chromatography were selected to determine BTEX in the soils. This method of SPME could not be used to analyze BTEX isomers in soils from highly contaminated sites because the high concentration of organic contaminants eroded the SPME probe head. The recoveries for added standard ranged from 95.2% - 98.2% for static headspace-GC and 99.2% - 101.3% for purge-and-trap-GC. When the soil samples contained low concentrations of BTEX (< 60 mg/kg), the concentration determined by purge-and-trap-GC was 12.6% - 37.6% higher than the value from static headspace-GC. For soil samples containing high concentrations of BTEX, the static headspace-GC result was higher than that from purge-and-trap-GC. The correlation trend lines of individual BTEX isomers to total BTEX were similar for both static headspace-GC and purge-and-trap-GC results.

[Chemical oxidants for remediation of BTEX-contaminated soils at coking sites].

An enclosed reactor was used to evaluate Fenton reagent, modified Fenton reagent, potassium permanganate and activated persulfate for removal of benzene, toluene, ethyl benzene, and xylene (BTEX) from soil at contaminated industrial coking sites. The results showed that Fenton reagent and modified Fenton reagent were the optimum oxidants for removing BTEX, and these oxidants decreased the concentration of BTEX in soils by 83% and 73%, respectively. The proportion of BTEX volatilized from the soil was < 4% in both cases, and the rates of BTEX removal from the whole system were 80% and 71%. More than 65% of xylene was removed after treatment with Fenton reagent and modified Fenton reagent. In contrast, benzene, toluene were more resistant to oxidation, and ethyl benzene was the most resistant of these compounds. The concentration of BTEX decreased to some extent when permanganate and activated persulfate were used as oxidants. However, the proportions of volatilized BTEX were 83% and 77% for permanganate and activated persulfate, respectively. This indicates that they could stimulate the desorption and volatilization of BTEX, while they were ineffective for removing BTEX from the environment.

[Enhancement of As-accumulation by Pteris vittata L. affected by microorganisms].

A pot experiment was carried out to study the root character and As accumulation of Pteris vittata L. affected by actinomycete PSQ, shf2 and bacteria Ts37, C13. The results indicated that growth of the fern was improved by the microorganisms. The biomass, root activity and root volume of shf2 treatment were 11.5 g/pot, 2.01 microg/(g x h), 38.3 mL, which were higher than those of other microorganisms treatments. Arsenic concentrations in the plants treated by the microorganisms were higher than that of the control treatment. The As concentration of leaves in Ts37 treatment was up to 837 mg/kg, 206% more than that of the control. The As concentration of root treated by shf2 is 427 mg/kg, 88% more than that of the control. The arsenic accumulation by the plant in microorganism treatments was higher than that of the control, especially shf2 treatment up to 5804 microg/pot, 136% more than that of the control. The phytoremediation efficiency of the fern in greenhouse experiment after 45d was from 8.9% to 11.3%. The ability of As-accumulation of Pteris vittata is greatly enhanced by application of microorganism, and actinomycete shf2 is proved as the perfect one.