Chronic impact of an accidental wastewater spill from a smelter, China: A study of health risk of heavy metal(loid)s via vegetable intake.

Chronic impact will last from a sudden pollution accident, however, potential adverse effects of heavy metal(loid)s are overlooked when pollution decreased during years of equilibration. Here, we assessed the potential health risks of heavy metal(loid)s via intake of vegetables from fields affected by the smelting wastewater spill eight years later, basing on site-specific target hazard quotient (STHQ) and cancer risk (SCR) models. Results showed kohlrabi, lettuce and garlic had significant high concentrations of Sb (10.4 mg kg-1), Pb (21.0 mg kg-1), Cd (6.49 mg kg-1), and Zn (441 mg kg-1), and sweet potato and garlic enriched high levels of As (19.6 mg kg-1) and Cu (14.1 mg kg-1), respectively. Transfer factors of metal(loid)s from soil to plants were enhanced by high soluble metal(loid) concentrations, and Sb, As, Pb and Cd in most edible tissues exceeded the contamination limitations for food in China and FAO/WHO. Chinese cabbage had significant high STHQ of As (adult 9.31 and child 19.8) and Sb (adult 0.76 and child 1.61) (p < 0.05), and the highest STHQ of Cd (adult 1.41 and child 3.02) was in lettuce, whereas the highest STHQ of other elements from vegetables were below 1. However, the non-carcinogenic risks based on total STHQ values of these vegetables were several times higher than the acceptable level of 1. In addition, the total SCR values at 5% were hundreds times of safety level of 5.0 × 10-5 set by International Commission on Radiological Protection. Considering food frequency and metal(loid) levels, long-term consumption of local vegetables, especially lettuce and Chinese cabbage, are likely to increase non-carcinogenic and carcinogenic (e.g. As and Cd) health risks. Child's health risk of toxic elements was far greater than adult. This study might serve as a case study of long-term adverse impact for other pollutant incidents. People should pay attention to human health through food chain, and the government should solve the outstanding environmental problems that harm the health of the masses.

Pyrolysis Temperature-Dependent Changes in the Characteristics of Biochar-Borne Dissolved Organic Matter and Its Copper Binding Properties.

The dissolved organic matter (DOM) samples from biochars produced from Jerusalem artichoke stalks by pyrolysis at 300, 500, and 700 °C were characterized using a combination of spectroscopic techniques. Additionally, the binding affinities (long KM) and the complexation capacities (CL) of the DOM samples with Cu(II) were calculated to assess their Cu binding properties. The biochar-borne DOM contained mainly humic-like components (C1-C3) with a small amount of a protein-like component (C4). As the charring temperature increased, the concentrations of released DOM decreased. The low temperature biochar-borne DOM was found to have more carboxyl groups than its high temperature counterparts, and thus it had larger CL values. In contrast, the high temperature biochar-borne DOM had larger long KM values. Low temperature biochars, if applied in a large quantity, would alter copper mobility in the environment because of their high DOM contents and large copper binding capacities.

Effect of biochar addition on short-term N2O and CO2 emissions during repeated drying and wetting of an anthropogenic alluvial soil.

Agricultural soils are an important source of greenhouse gases (GHG). Biochar application to such soils has the potential of mitigating global anthropogenic GHG emissions. Under irrigation, the topsoils in arid regions experience repeated drying and wetting during the crop growing season. Biochar incorporation into these soils would change the soil microbial environment and hence affect GHG emissions. Little information, however, is available regarding the effect of biochar addition on carbon dioxide (CO2) and nitrous oxide (N2O) emissions from agricultural soils undergoing repeated drying and wetting. Here, we report the results of a 49-day aerobic incubation experiment, incorporating biochar into an anthropogenic alluvial soil in an arid region of Xinjiang Province, China, and measuring CO2 and N2O emissions. Under both drying-wetting and constantly moist conditions, biochar amendment significantly increased cumulative CO2 emission. At the same time, there was a significant reduction (up to ~20 %) in cumulative N2O emission, indicating that the addition of biochar to irrigated agricultural soils may effectively slow down global warming in arid regions of China.

Diurnal and spatial variations of soil NOx fluxes in the northern steppe of China.

NOx emissions from biogenic sources in soils play a significant role in the gaseous loss of soil nitrogen and consequent changes in tropospheric chemistry. In order to investigate the characteristics of NOx fluxes and factors influencing these fluxes in degraded sandy grasslands in northern China, diurnal and spatial variations of NOx fluxes were measured in situ. A dynamic flux chamber method was used at eight sites with various vegetation coverages and soil types in the northern steppe of China in the summer season of 2010. Fluxes of NOx from soils with plant covers were generally higher than those in the corresponding bare vegetation-free soils, indicating that the canopy plays an important role in the exchange of NOx between soil and air. The fluxes of NOx increased in the daytime, and decreased during the nighttime, with peak emissions occurring between 12:00 and 14:00. The results of multiple linear regression analysis indicated that the diurnal variation of NOx fluxes was positively correlated with soil temperature (P<0.05) and negatively with soil moisture content (P<0.05). Based on measurement over a season, the overall variation in NOx flux was lower than that of soil nitrogen contents, suggesting that the gaseous loss of N from the grasslands of northern China was not a significant contributor to the high C/N in the northern steppe of China. The concentration of NOx emitted from soils in the region did not exceed the 1-hr National Ambient Air Quality Standard (0.25 mg/m3).

Fabrication and environmental applications of metal-containing solid waste/biochar composites: A review.

The resource utilization of industrial solid waste has become a hot issue worldwide. Composites of biochar with metal-containing solid wastes (MCSWs) can not only improve the adsorption performance, but also reduce the cost of modification and promote the recycling of waste resources. Thus, the synthesis and applications of biochar composites modified by MCSWs have been attracting increasing attention. However, different MCSWs may result in metal-containing solid waste/biochar composites (MCSW-BCs) with various physicochemical properties and adsorption performance, causing distinct adsorption mechanisms and applications. Although a lot of researches have been carried out, it is still in infancy. In particular, the explanation on the adsorption mechanisms and influencing factors of pollutant onto MCSW-BCs are not comprehensive and clear enough. Therefore, a systematic review on fabrication and potential environmental applications of different MCSW-BCs is highly needed. Here we summarize the recent advances on the utilization of typical metal-containing solid wastes, preparation of MCSW-BCs, adsorption mechanisms and influencing factors of pollutants by MCSW-BCs as well as their environmental applications. Finally, comments and perspectives for future studies are proposed.

Formation and mechanisms of nano-metal oxide-biochar composites for pollutants removal: A review.

Biochar, a carbon-rich material, has been widely used to adsorb a range of pollutants because of its low cost, large specific surface area (SSA), and high ion exchange capacity. The adsorption capacity of biochar, however, is limited by its small porosity and low content of surface functional groups. Nano-metal oxides have a large SSA and high surface energy but tend to aggregate and passivate because of their fine-grained nature. In combining the positive qualities of both biochar and nano-metal oxides, nano-metal oxide-biochar composites (NMOBCs) have emerged as a group of effective and novel adsorbents. NMOBCs improve the dispersity and stability of nano-metal oxides, rich in adsorption sites and surface functional groups, maximize the adsorption capacity of biochar and nano-metal oxides respectively. Since the adsorption capacity and mechanisms of NMOBCs vary greatly amongst different preparations and application conditions, there is a need for a review of NMOBCs. Herein we firstly summarize the recent methods of preparing NMOBCs, the factors influencing their efficacy in the removal of several pollutants, mechanisms underlying the adsorption of different pollutants, and their potential applications for pollution control. Recommendations and suggestions for future studies on NMOBCs are also proposed.

Carbon-coated montmorillonite nanocomposite for the removal of chromium(VI) from aqueous solutions.

A carbon-coated montmorillonite nanocomposite (CMt), obtained by hydrothermal carbonization of montmorillonite suspension in glucose, was used to remove Cr(VI) from aqueous solutions. The distribution and speciation of Cr immobilized by CMt were assessed by transmission electron microscopy with energy-dispersive X-ray analysis, X-ray absorption near edge structure (XANES), and scanning transmission soft X-ray microscopy (STXM). The variation in the functional groups and molecular structures of CMt was also investigated. The capacity of CMt for adsorbing Cr(VI) was markedly superior to that of the parent montmorillonite, showing maximum uptake of 100 and 12.4 mg g-1 at pH 2 and 8, respectively. The Cr K-edge XANES and STXM analyses indicated that Cr(VI) was reduced to Cr(III) under both acidic and alkaline conditions, while a Cr(OH)3 precipitate and Cr(III)-acetate complex were the predominant species present on the CMt surface. The Fourier transform infrared spectroscopy and C K-edge XANES further suggested that the phenolic groups in CMt could serve as electron donors, facilitating Cr(VI) reduction. The combined results indicate that electrostatic attraction, Cr(VI) reduction, complexation, and precipitation are involved in the removal of Cr(VI) by CMt.

Assessing the effect of pyrolysis temperature on the molecular properties and copper sorption capacity of a halophyte biochar.

The capacity of biochar to take up heavy metals from contaminated soil and water is influenced by the pyrolysis temperature. We have prepared three biochar samples from Jerusalem artichoke stalks (JAS) by pyrolysis at 300, 500 and 700 °C, denoted as JAS300, JAS500, and JAS700, respectively. A variety of synchrotron-based techniques were used to assess the effect of pyrolysis temperature on the molecular properties and copper (Cu) sorption capacity of the samples. The content of oxygen-containing functional groups in the biochar samples decreased, while that of aromatic structures and alkaline mineral components increased, with a rise in pyrolysis temperature. Scanning transmission X-ray microscopy indicated that sorbed Cu(II) was partially reduced to Cu(I), but this process was more evident with JAS300 and JAS700 than with JAS500. Carbon K-edge X-ray absorption near edge structure spectroscopy indicated that Cu(II) cations were sorbed to biochar via complexation and Cu-π bonding. With rising pyrolysis temperature, Cu(II)-complexation weakened while Cu-π bonding was enhanced. In addition, the relatively high ash content and pH of JAS500 and JAS700 facilitated Cu precipitation and the formation of langite on the surface of biochar. The results of this investigation will aid the conversion of halophyte waste to useable biochar for the effective remediation of Cu-contaminated soil and water.

Lipid peroxidation and cytotoxicity induced by respirable volcanic ash.

This paper reports that the main component of respirable volcanic ash, allophane, induces lipid peroxidation (LP), the oxidative degradation of lipids in cell membranes, and cytotoxicity in murin monocyle/macrophage cells. Naturally-occurring allophane collected from New Zealand, Japan, and Ecuador was studied. The quantification of LP was conducted using the Thiobarbituric Acid Reactive Substances (TBARS) assay. The cytotoxic effect was determined by the 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide colorimetric assay. Electron-Paramagnetic Resonance (EPR) determinations of naturally-occurring allophane confirmed the incorporation in the structure and clustering of structural Fe(3+), and nucleation and growth of small-sized Fe (oxyhydr)oxide or gibbsite. LP induced by allophane varied with time, and solid concentration and composition, reaching 6.7 ± 0.2 nmol TBARS mg prot(-1). LP was surface controlled but not restricted by structural or surface-bound Fe(3+), because redox processes induced by soluble components other than perferryl iron. The reactivity of Fe(3+) soluble species stemming from surface-bound Fe(3+) or small-sized Fe(3+) refractory minerals in allophane surpassed that of structural Fe(3+) located in tetrahedral or octahedral sites of phyllosilicates or bulk iron oxides. Desferrioxamine B mesylate salt (DFOB) or ethylenediaminetetraacetic acid (EDTA) inhibited LP. EDTA acted as a more effective inhibitor, explained by multiple electron transfer pathways. Registered cell-viability values were as low as 68.5 ± 6.7%.

Chemical and mineralogical composition of the Mongolian rural soils and their uranium sorption behavior.

Distribution of uranium (VI) between soil solids and solutions is a key parameter in assessing the risk to the biosphere of disposing uranium-rich waste products from nuclear plants as well as uranium (U) ore mining. Both of these topics have recently been brought to public attention in Mongolia. Regional background levels of soil elements are an important dataset for accessing the actual environmental situation and monitoring pollution levels. Little information, however, is available on background concentrations of various elements in Mongolian soils. Thirteen rural soils were sampled from six provinces in Mongolia, and the concentrations of macro-, micro- and trace elements were measured. The values obtained served as a reference (baseline) for uncontaminated soils. The soils were characterized with slightly acidic to strongly alkaline pH values. With the exception of the sample from a western province, all the soils investigated contained little organic matter. The content of soil elements did not vary widely among geographical regions. The concentration of most micro elements was within the range of worldwide soil values but the value for Zn tended to be moderately higher. The U (VI) sorption into the soils was investigated using the batch technique and the (237)U radionuclide tracer, produced by the photo fission reaction (238)U(γ, n) (237)U at an electron accelerator. The (237)U distribution coefficient (K(d)), derived from the sorption isotherms, was related to solution pH and varying from 9 to 2547 mL g(-1) when the pH ranged between 3 and 7.7. The sorption process was interpreted in terms of the formation of different U (VI) species at given concentrations, calculated using the Speciation program with and without carbonate in the system. The U sorption isotherm displayed two general patterns: one where sorption decreased as solution pH increased, showing a maximum at pH 3, and another pattern revealed an adsorption maximum at pH 5 and then decreased up to pH 7.7 (the final solution pH). The observed decrease in K(d) when solution pH increased from 6 to 8 was consistent with the increased formation of soluble UO(2)(OH)(2) species. A linear negative correlation between lgK(d) and the solution pH was observed similarly to that reported for the soils with a pH ≥ 6.