Arsenic accumulation and resistance mechanism in Panax notoginseng, a traditional rare medicinal herb

Panax notoginseng, a traditional rare Chinese medicinal herb, was recently found to bring health risk to consumers, mainly because soil in its major plantation area was contaminated by arsenic (As). We investigated the effect of soil As pollution on the growth and As uptake of pot-cultured P. notoginseng, and the associated mechanisms of As stressed response. Results showed that, comparing with P. notoginseng growing in a low-As soil, the root, stem, and leaf biomasses of those growing in a high-As soil significantly reduced by 0.75, 0.09 and 0.21 g seedling⁻¹, respectively. Arsenic concentrations in roots, stems and leaves of the seedlings growing in high-As soil were 22, 15 and 3 times higher than those growing in low-As soil, respectively. Regardless of the soil As concentration, As existed in plants mainly as As(III), suggesting that the reduction of As(V) is a key step in As metabolism. Arsenic was distributed primarily in cell walls (51.7% for plants growing in the low-As soil, and 51.5% in the high-As soil), followed by cytoplasm supernatant, with cell organelles containing the least As. Compared with plants growing in the low-As soil, those in the high-As soil had increased superoxide dismutase and peroxidase activities in their roots, stems, and leaves, which would be associate with improving the resistance of P. notoginseng to As stress. The results suggest that there exists some special mechanisms of As-tolerance in P. notoginseng and the study is of significance in developing measures to reduce As in the herb.     

Selenium speciation and localization in chironomids from lakes receiving treated metal mine effluent

A lake system in northern Saskatchewan receiving treated metal mine and mill effluent contains elevated levels of selenium (Se). An important step in the trophic transfer of Se is the bioaccumulation of Se by benthic invertebrates, especially primary consumers serving as a food source for higher trophic level organisms. Chironomids, ubiquitous components of many northern aquatic ecosystems, were sampled at lakes downstream of the milling operation and were found to contain Se concentrations ranging from 7 to 80 mg kg⁻¹ dry weight. For comparison, laboratory-reared Chironomus dilutus were exposed to waterborne selenate, selenite, or seleno-DL-methionine under laboratory conditions at the average total Se concentrations found in lakes near the operation. Similarities in Se localization and speciation in laboratory and field chironomids were observed using synchrotron-based X-ray fluorescence (XRF) imaging and X-ray absorption spectroscopy (XAS). Selenium localized primarily in the head capsule, brain, salivary glands and gut lining, with organic Se species modeled as selenocystine and selenomethionine being the most abundant. Similarities between field chironomids and C. dilutus exposed in the laboratory to waterborne selenomethionine suggest that selenomethionine-like species are most readily accumulated, whether from diet or water.     

Evaluating mobilization and transport of arsenic in sediments and groundwaters of Aquia aquifer, Maryland, USA

Groundwater and sediment samples were collected along a flow path in the Aquia aquifer (Paleocene), Maryland in order to examine and study the factors influencing "evolution" of arsenic (As) in these groundwaters. The Aquia crops out near Washington, DC, where it is unconfined, and extends approximately 90 km down dip to the south and east towards and beneath the Chesapeake Bay. The studied flow path was chosen owing to (i) the number of accessible wells, (ii) differences in total dissolved As concentrations in groundwaters from some of the sampled wells, which reach values >/=667 nmol kg(-1) or >/=50 ppb, and (iii) the distinct difference in total dissolved As concentrations in Aquia groundwaters between the northern and southern portions of the study area. In groundwater samples, in situ separation of inorganic As species [As(III) and As(V)] were performed by using anion exchange chromatography. Subsequently, As concentrations were determined by inductively coupled plasma mass spectrometry. In situ measurements of Fe concentrations and speciation, dissolved S(-II) concentrations, pH, alkalinity, and oxidation-reduction potential (Eh) were determined to establish the oxidation-reduction conditions and solution chemistry along the flow path. Concentrations of As in 12 analyzed groundwater samples range from approximately 0.75 to 1 072 nmol kg(-1), and As(III) concentrations ranging from 0.24 to 980 nmol kg(-1) appears to be the dominant form of As in solution. 50% of the studied wells yielded groundwaters with concentrations that exceed the US EPA's Maximum Contaminant Level for As in drinking water of 133 nmol kg(-1) or 10 ppb. In order to examine the solid phase speciation of As within the aquifer sediments, we collected a number of Aquia sediment samples from a drill core that was archived at the Maryland Geological Survey. These sediment samples were evaluated using a previously established sequential extractions procedure. Solid phase As concentrations range between 973 and 2,012 nmol kg(-1). Additionally, petrographic, X-Ray diffraction and diffuse reflectance spectroscopy analyses of the Aquia sediments reveal presence of glauconite, and smectite along with goethite and hematite within the samples. Here, we present the possible mechanisms responsible for the elevated As concentrations in the studied groundwaters of the Aquia aquifer.     

北方某水库表层沉积物重金属的赋存形态及其环境影响因子分析

为了解北方某水库重金属污染状况,采用BCR连续提取法对该水库表层沉积物中Cu、Pb、Zn、Cd的赋存形态进行了分析,对其含量及空间分布进行了研究,结合重金属总量讨论了各元素的潜在环境风险。结果表明,该水库表层沉积物中Cu、Pb、Zn、Cd的平均质量比分别为65.20 mg/kg、36.69 mg/kg、137.5 mg/kg、2.38 mg/kg,与该地区土壤元素背景值、该地区水系沉积物平均值及全国水系沉积物平均值相比,4种重金属元素均有一定程度的累积,其中Cd累积最为严重。形态分析结果表明,Cd主要以醋酸可提取态及可还原态存在,具有很高的环境风险;Pb主要以极高比例的可还原态存在,潜在风险较高;Zn和Cu存在较大比例的酸可提取态及可还原态,也具有一定程度的潜在风险。各元素生物有效性即可提取态含量排序为:Cd>Cu>Pb>Zn。     

An approach for arsenic in a contaminated soil: Speciation, fractionation, extraction and effluent decontamination

The fractionation and speciation of As in a contaminated soil were investigated, and a remediation strategy was tested. Regarding speciation, we found that As(V) prevails over As(III) whereas more than 40% of total arsenic is in organic form. The fractionation of As was investigated with two sequential extraction methods: a low mobility was found. Then we tested the possibility of using phosphoric acid to extract As from the soil and cleaning the washing effluents by sorption onto montmorillonite. The efficiency of the extraction and of the adsorption onto the clay were also investigated for Cr, Cu, Fe, Mn, Ni, Pb and Zn, whose total concentrations and fractionation in the soil are reported here. The extraction percentages for As and metals ranged from 30 to 65%; the residual proportions in the soil are presumably in very unreactive forms. Montmorillonite showed a good uptake capacity towards the investigated pollutants.     

Effects of substrate types on the transformation of heavy metal speciation and bioavailability in an anaerobic digestion system

Chemical speciation can fundamentally affect the potential toxicity and bioavailability of heavy metals. The transformation of heavy metal speciation and change of bioavailability were investigated in an anaerobic digestion (AD) system using four different substrates (pig manure (PM), cattle manure (CAM), chicken manure (CHM) and rice straw (RS)). The results obtained indicated that the total contents of heavy metals in PM, CHM and CAM were higher than in RS and decreased in the order Zn > Cu > Ni > Pb > As > Cd in all substrates. Moreover, the speciation with the largest proportion for each heavy metal was the same both in the different substrates and the biogas residues. Among them, Zn, Ni, Cd and As were mainly in the reducible fraction (F2), while Cu was mainly in the oxidizable fraction (F3) and Pb occurred predominantly in the residual fraction (F4). Our results further indicated that the AD process had a greater effect on the speciation of heavy metals in CHM and PM, but less on CAM and RS. The rates of change in bioavailability followed the order PM > CHM > CAM > RS. Changes in organic matter, humic acid or local metal ion environment as a result of AD were inferred as likely mechanisms leading to the transformation of heavy metal speciation. These results enhanced our understanding of the behavior of heavy metals in AD and provided a new perspective for the treatment and disposal of the substrates.     

城市污水厂污泥中重金属去除及其土地利用的研究现状

污泥中富含磷、氮和钾等农作物需要的营养物质,但碍于污泥中残留的重金属离子而难以使用.文章介绍了污泥中重金属的存在形式及作用机理,综述了几种能有效去除重金属的方法(吸附法、淋滤法和化学法),分析了各种方法的优缺点、影响因素、处理效果、适用范围及处理后土地利用的现状,以期处理后的污泥能够作为农用土地,减轻剩余污泥二次污染危...     

A simple voltammetric procedure for speciation and evaluation of As removal from water

Here, we show a fast and sensitive method for the determination of inorganic arsenic in natural waters using differential pulse cathodic stripping voltammetry. All the arsenite determinations were done in 2.0 mol L⁻¹ HCl + 3.15 × 10⁻⁴ mol L⁻¹ Cu(II) supporting electrolyte. 1 × 10⁻³ mol L⁻¹ sodium thiosulphate was used as As(V) reducing agent. The detection limit was 0.5 μg L⁻¹ for both species. The method has been applied to water samples collected in an arsenic-contaminated region of Brazil, in particular, to verify the efficiency of the solar oxidation and removal of arsenic process applied to these waters.     

环境样品中铅、锑、汞、硒形态分析研究进展

综述了环境样品中铅、锑、汞、硒形态分析的研究进展,以及光谱法、色谱法、毛细管电泳及其联用技术在形态分析中的应用,展望了环境样品痕量元素形态分析的发展前景。     

Roles of pyrolysis on availability,species and distribution of Cu and Zn in the swine manure: Chemical extractions and high-energy synchrotron analyses

Animal manures generally contain high levels of heavy metals that may pose a significant threat to soil and groundwater qualities. Pyrolysis as means of reducing metal availability in such feed stocks is recently encouraged, but systematic studies are currently lacking. The aim of this study was to assess the impact of pyrolysis temperature on the availability of Cu and Zn by chemical extraction, to determine the speciation of Cu and Zn by synchrotron-based X-ray spectroscopy, and finally to investigate the phase distribution of metal species in the carbonaceous materials by combining acid–base extractions and absorption spectroscopy data. The results showed that both Cu and Zn in the swine manure were mainly bound to organic functional groups. Cu (II) reduction and Cu (I)–S complexes were observed during the pyrolysis process. Zn species resembling ZnAc₂ was still dominant, being 60.8–69.2%, and ZnS increased by 6.6–21.8% in the carbonaceous materials. The distribution of Cu and Zn in the mineral, carbonized and non-carbonized organic phases varied greatly with the pyrolysis temperature. The higher the temperature, the more the metals existed in the mineral phase and carbonized organic phase. The decrease of EDTA extractable Cu and Zn with pyrolysis temperature was due to the increase of metals in the carbonized organic phase and mineral phase. It is suggested that pyrolysis at the relatively higher temperature is a better choice for metal-containing manure according to the metal speciation, solubility and availability.