Rice: Reducing arsenic content by controlling water irrigation

<正>Arsenic has long been recognized as a poison.Arsenic in water supplies that are used for both drinking and crop irrigation can expose many people chronically to elevated levels of arsenic.The main health concern for chronic exposure to arsenic is the development of cancer.Although the World Health Organization(WHO)recommends that total arsenic in drinking water should be under 10μg/L(or 10 ppb),(WHO,2011),some regions     

Arsenic fractionation and contamination assessment in sediments of thirteen lakes from the East Plain and Yungui Plateau Ecoregions, China

Arsenic（As） fractions in the sediments of seven lakes from East Plain Ecoregion and six lakes from Yungui Plateau Ecoregion, China, were investigated. Results indicated that the total As concentrations in sediment samples of lakes of the East Plain Lake Ecoregion are higher than those of Yungui Plateau Lake Ecoregion. Residual As is the main fraction in sediment samples of lakes from both ecoregions, followed by reducible As and soluble or oxidizable As. The total As is correlated to oxidizable As and residual As in sediment samples from both lake ecoregions. As distribution in sediment samples of lakes of the East Plain Ecoregion appears to be affected by human activity, while the As origin mainly comes from natural sources in sediment samples of lakes in the Yungui Plateau Ecoregion. The potential ecological risk index and geoaccumulation index values suggest ＂low to moderate＂ risk degree and ＂unpolluted to moderately polluted＂ for As in the studied lake sediments.     

植物中锌同位素的研究进展

锌同位素是示踪植物中锌地球化学的重要手段,详细了解植物中锌同位素的分馏过程是探究其生物地球化学的关键。本文对目前研究程度较高的超富集植物、普通植物的锌同位素分馏成果进行了系统的总结,发现二者锌同位素分馏趋势基本一致,即相比于培养液或土壤的同位素组成,植物根部相对富集锌的重同位素,而植物地上部(如茎、叶等组织器官)相对富集锌的轻同位素。对于能够引起植物发生锌同位素分馏的因素归纳如下:(1)植物根部相对富集锌的重同位素,是土壤中锌的形态、根部对锌的吸收方式、细胞表面吸附共同作用的结果;(2)植物木质部对锌的向上运输,会随着传输距离的增加而使地上部组织器官相对富集锌的轻同位素;(3)大气沉降也可能导致叶片富集锌的轻同位素。     

微波消解-双道原子荧光分析仪联合测定土壤中砷和汞

应用AFS-9530型双道原子荧光光谱法研究土壤样品中砷和汞的联合测定技术,将土壤样品置于(1+1)王水的微波消解体系中进行消解,加入1m L 5%的重铬酸钾溶液保护汞,加入5m L(5%硫脲+5%抗坏血酸)混合液将五价砷还原为三价,以硼氢化钾为还原剂在5%盐酸介质中测定砷和汞,最低检出限为砷0.55μg/L,汞0.30μg/L,回收率砷在93.5%—105.8%之间,汞在85.5%—104.9%之间,满足准确度要求。     

南京市城市污泥和工业污泥中典型矿质元素含量和形态分布研究

采用三态连续提取法研究南京市部分城市污泥和工业污泥中典型矿质元素的含量和形态分布,为污泥资源化的合理利用提供科学参考.结果表明,污泥总体呈高有机质、高氮磷、低K的相似性,但其理化性质如阳离子交换容量(CEC)、pH等有差异.污泥中不同矿质元素含量差异也较大,Fe的浓度最高,其次是Mg、Zn;且不同污泥间同一矿质元素含量的差异也较大.各元素的形态分布有一定差异,Cu主要分布在可氧化态,其酸溶/交换态和可还原态的百分率很低;Zn三态分布均较高;Mg、Mn主要分布在酸溶/交换态;Fe主要分布在残渣态.但三种提取形态百分率之和除Fe外均超过50%.研究同时表明,城市污泥和工业污泥中矿质元素形态分布无显著性差异.     

Geochemistry of leachates from the El Fraile sulfide tailings piles in Taxco, Guerrero, southern Mexico

Leachates from the El Fraile tailings impoundment (Taxco, Mexico) were monitored every 2 months from October 2001 to August 2002 to assess the geochemical characteristics. These leachates are of interest because they are sometimes used as alternative sources of domestic water. Alternatively, they drain into the Cacalotenango creek and may represent a major source of metal contamination of surface water and sediments. Most El Fraile leachates show characteristics of Ca–SO₄, (Ca+Mg)–SO₄, Mg–SO₄ and Ca–(SO₄+HCO₃) water types and are near-neutral (pH=6.3–7.7). Some acid leachates are generated by the interaction of meteoric water with tailings during rainfall events (pH=2.4–2.5). These contain variable levels of SO₄ ²⁻ (280–29,500 mg l⁻¹) and As (<0.01–12.0 mg l⁻¹) as well as Fe (0.025–2352 mg l⁻¹), Mn (0.1–732 mg l⁻¹), Zn (<0.025–1465 mg l⁻¹) and Pb (<0.01–0.351 mg l⁻¹). Most samples show the highest metal enrichment during the dry seasons. Leachates used as domestic water typically exceed the Mexican Drinking Water Guidelines for sulfate, hardness, Fe, Mn, Pb and As, while acidic leachates exceed the Mexican Guidelines for Industrial Discharge Waters for pH, Cu, Cd and As. Speciation shows that in near-neutral solutions, metals exist mainly as free ions, sulfates and bicarbonates, while in acidic leachates they are present as sulfates and free ions. Arsenic appears as As^(V) in all samples. Thermodynamic and mineralogical evidence indicates that precipitation of Fe oxides and oxyhydroxides, clay minerals and jarosite as well as sorption by these minerals are the main processes controlling leachate chemistry. These processes occur mainly after neutralization by interaction with bedrock and equilibration with atmospheric oxygen.     

Fate of arsenic compounds in poultry litter upon land application

The use of the organic As compound, roxarsone, as an antibiotic additive to poultry feed continues to raise concern over potential negative environmental impacts. Total As concentration in poultry litter can reach >40 mg kg⁻¹ and both roxarsone and its mineralization product As(V) have been identified in poultry litters (PL). To investigate the fate of these As species upon land application of PL we conducted two studies. In the first, an Orangeburg soil (Ultisol from the Atlantic Coastal Plain) was spiked with either 20 mg kg⁻¹ As(V) or roxarsone and incubated at 10% moisture content for 4 months. Exchangeable As was determined periodically by extraction with 0.1 M PO₄. Both As(V) and roxarsone displayed similar desorption; initially, approximately 70% of added As was ligand exchangeable and this decreased to 35% after 4 months incubation, presumably due to either slow sorption reactions or a change in solid phase speciation of As to less exchangeable forms. In the second study, various manipulations of two PL samples were applied to the Orangeburg soil at realistic field application rates. The treatments were wet to 10% moisture content and water soluble As, Cu and organic carbon (DOC) was measured over 30 days. Arsenic and Cu solubility were highest from the dried litter samples. Ashing of the PLs decreased soluble As and Cu, presumably because of the loss of organic matter from the ashed litter and subsequent decrease in DOC. Application of leachates from either PL resulted in higher concentrations of soluble As and Cu than when the soil was amended with equivalent concentrations of soluble As and Cu dissolved in DI H₂O. We hypothesize that the increased levels of DOC from the PL treatments enhance As and Cu solubility through competitive sorption and complexation, respectively. In fact, As and Cu solubility was correlated to DOC levels in the amended soil extracts. Even though land application of PL introduced relatively low concentrations of As and Cu to soil it appeared that other soluble constituents of PL significantly enhanced As and Cu solubility.     

Isolation and Identification of Antialgal Compounds from the Leaves of Vallisneria spiralis L. by Activity-Guided Fractionation (5 pp)

Background, Aims and Scope

Vallisneria spiralis Linn., a common, submerged macrophyte, is widely available in quiet waters of lakes, ponds, marshes and streams in Southeast Asia. V. spiralis plays a significant role not only in decreasing eutrophication of water body for its productivity, but also in inhibiting the growth of blue-green algae? The aim of the paper involves the isolation and identification of allelochemicals from extracts of V. spiralis by activity-guided fractionation and column chromatography.

Methods

Leaves of V. spiralis was washed free of debris, air-dried and refluxed in 95% EtOH. The extract was isolated using column chromatography and fractionation with antialgal activity. Potential allelochemicals were analyzed by high-resolution gas chromatography-mass spectrometry (HRGC-MS).

Results

Two fractions with strong antialgal activity were isolated using column chromatography and activity-guided fractionation from the extract of V. spiralis. 2-Ethyl-3-methylmaleimide, dihydroactinidiolide and 4-oxo-β-Ionone were identified in the first fraction, and 3-hydroxy-5,6-epoxy-β-ionone, loliolide, 6-hydroxy-3-oxo-α-ionone and an unknown compound in the second fraction. They had strong inhibitory effects on Microcystis aeruginosa Kütz.

Discussion

2-Ethyl-3-methylmaleimide is a byproduct of photooxidation of chlorophyll, and five other compounds identified were derivatives of β-carotene. HRGC-MS and derivatization technology were used to identify and confirm their molecular structures. The formula of the unknown compound was C16H19NO4. Metabolites of plant pigments had strong inhibitory activities on growth of algae.

Conclusions

Six compounds had been identified in V. spiralis, among them, 2-ethyl-3-methylmaleimide was the main allelochemical, and derivatives of ionone were also potential allelochemicals.

Recommendations and Perspective

. The results of our research could help us to study further mechanisms of inhibitory effect on algae and develop new potential antialgal substances.     

土壤中重金属形态的化学分析综述

土壤中重金属的赋存形态决定其在土壤中的迁移性、生物可利用性以及毒性.土壤中重金属形态的化学分析法是依据不同浸取能力的提取剂分别提取出与土壤颗粒有着不同结合力的化学形态并测定其浓度而建立起来的.文章对土壤重金属形态分析中选用的提取试剂以及分析流程进行了综述,比较了各种试剂和方法的优缺点.同时对形态分析的土壤样品的前处理方式进行了简要概述.