同位素稀释质谱在食品与环境分析中的应用

介绍了同位素稀释质谱的测量过程、分类及其联用技术,阐述了该技术在食品与环境分析中的应用进展。     

Predicting arsenic solubility in contaminated soils using isotopic dilution techniques

An isotopic dilution assay was developed to measure radiolabile As concentration in a diverse range of soils (pH 3.30-7.62; % C = 1.00-6.55). Soils amended with 50 mg of As kg(-1) (as Na2HAsO4 x 7H2O) were incubated for over 800 d in an aerated "microcosm" experiment. After 818 d, radiolabile As ranged from 27 to 57% of total applied As and showed a pH-dependent increase above pH 6. The radiolabile assay was also applied to three sets of soils historically contaminated with sewage sludge or mine-spoil. Results reflected the various geochemical forms in which the arsenic was present. On soils from a sewage disposal facility, radiolabile arsenate ranged from 3 to 60% of total As; mean lability was lower than in the equivalent pH range of the microcosm soils, suggesting occlusion of As into calcium phosphate compounds in the sludge-amended soils. In soils from mining areas in the U.K. and Malaysia, radiolabile As accounted for 0.44-19% of total As. The lowest levels of lability were associated with extremely large As concentrations, up to 17,000 mg kg(-1), from arsenopyrite. Soil pore water was extracted from the microcosm experiment and speciated using "GEOCHEM". The solid<==>solution equilibria of As in the microcosm soils was described by a simple model based on competition between HAsO4(2-) and HPO4(2-) for "labile" adsorption sites.     

Release of arsenic to the environment from CCA-treated wood. 1. Leaching and speciation during service

Insufficient information exists about the speciation of arsenic leaching from in-service chromated copper arsenate (CCA)-treated products and the overall impact to soils and groundwater. To address this issue, two decks were constructed, one from CCA-treated wood and the other from untreated wood. Both decks were placed in the open environment where they were impacted by rainfall. Over a one-year period, rainwater runoff from the decks and rainwater infiltrating through 0.7 m of sand below the decks was collected and analyzed for arsenic species by HPLC-ICP-MS. The average arsenic concentration in the runoff of the untreated deck was 2-3 microg/L, whereas from the CCA-treated deck it was 600 microg/L. Both inorganic As(III) and As(V) were detected in the runoff from both decks, with inorganic As(V) predominating. No detectable levels of organoarsenic species were observed. The total arsenic concentration in the infiltrated water of the treated deck had risen from a background concentration of 3 microg/L to a concentration of 18 microg/L at the end of the study. Data from the deck study were combined with annual CCA-treated wood production statistics to develop a mass balance model to estimate the extent of arsenic leaching from in-service CCA-treated wood structures to Florida soils. Results showed that during the year 2000, of the 28 000 t of arsenic imported into the state and utilized for in-service CCA-treated wood products, approximately 4600 t had already leached. Future projections suggest that an additional 11,000 t of arsenic will leach during in-service use within the next 40 years.     

Release of arsenic to the environment from CCA-treated wood. 2. Leaching and speciation during disposal

Wood treated with chromated copper arsenate (CCA) is primarily disposed within construction and demolition (C&D) debris landfills, with wood monofills and municipal solid waste (MSW) landfills as alternative disposal options. This study evaluated the extent and speciation of arsenic leaching from landfills containing CCA-treated wood. In control lysimeters where untreated wood was used, dimethylarsinic acid (DMAA) represented the major arsenic species. The dominant arsenic species differed in the lysimeters containing CCA-treated wood, with As(V) greatest in the monofill and C&D lysimeters and As(III) greatest in the MSW lysimeters. In CCA-containing lysimeters, the organoarsenic species monomethylarsonic acid (MMAA) and DMAAwere virtually absent in the monofill lysimeter and observed in the C&D and MSW lysimeters. Overall arsenic leaching rate varied for the wood monofill (0.69% per meter of water added), C&D (0.36% per m), and MSW (0.84% per m) lysimeters. Utilizing these rates with annual disposal data, a mathematical model was developed to quantify arsenic leaching from CCA-treated wood disposed to Florida landfills. Model findings showed between 20 and 50 t of arsenic (depending on lysimeter type) had leached prior to 2000 with an expected increase between 350 and 830 t by 2040. Groundwater analysis from 21 Florida C&D landfills suspected of accepting CCA-treated wood showed that groundwater at 3 landfills was characterized by elevated arsenic concentrations with only 1 showing impacts from the C&D waste. The slow release of arsenic from disposed treated wood may account for the lack of significant impact to groundwater near most C&D facilities at this time. However, greater impacts are anticipated in the future given that the maximum releases of arsenic are expected by the year 2100.     

Assessing the labile arsenic pool in contaminated paddy soils by isotopic dilution techniques and simple extractions

Arsenic (As) contamination of paddy soils threatens rice cultivation and the health of populations relying on rice as a staple crop. In the present study, isotopic dilution techniques were used to determine the chemically labile (E value) and phytoavailable (L value) pools of As in a range of paddy soils from Bangladesh, India, and China and two arable soils from the UK varying in the degree and sources of As contamination. The E value accounted for 6.2-21.4% of the total As, suggesting that a large proportion of soil As is chemically nonlabile. L values measured with rice grown under anaerobic conditions were generally larger than those under aerobic conditions, indicating increased potentially phytoavailable pool of As in flooded soils. In an incubation study, As was mobilized into soil pore water mainly as arsenite under flooded conditions, with Bangladeshi soils contaminated by irrigation of groundwater showing a greater potential of As mobilization than other soils. Arsenic mobilization was best predicted by phosphate-extractable As in the soils.     

Investigating arsenic speciation and mobilization in sediments with DGT and DET: a mesocosm evaluation of oxic-anoxic transitions

Mobilization of arsenic from freshwater and estuarine sediments during the transition from oxic to anoxic conditions was investigated using recently developed diffusive sampling techniques. Arsenic speciation and Fe(II) concentrations were measured at high resolution (1-3 mm) with in situ diffusive gradients in thin films (DGT) and diffusive equilibration in thin films (DET) techniques. Water column anoxia induced Fe(II) and As(III) fluxes from the sediment. A correlation between water column Fe(II) and As(III) concentrations was observed in both freshwater (r(s) = 0.896, p < 0.001) and estuarine (r(s) = 0.557, p < 0.001) mesocosms. Porewater sampling by DGT and DET techniques confirmed that arsenic mobilization was associated with the reductive dissolution of Fe(III) (hydr)oxides in the suboxic zone of the sediment; a relationship that was visible because of the ability to measure the coincident profiles of these species using combined DGT and DET samplers. The selective measurement of As(III) and total inorganic arsenic by separate DGT samplers indicated that As(III) was the primary species mobilized from the solid phase to the porewater. This measurement approach effectively ruled out substantial As(V) mobilization from the freshwater and estuarine sediments in this experiment. This study demonstrates the capabilities of the DGT and DET techniques for investigating arsenic speciation and mobilization over a range of sediment conditions.     

砷及砷的形态检测方法的研究现状

砷是一种广泛分布于自然界的微量元素,摄入过量砷元素容易引起砷的急性中毒而致死,应引起人们足够的重视。砷的毒性主要取决于它的化学形态,形态不同毒性差异很大,所以选择适当、简便、快速的测定方法是现代分析技术取得发展的必要条件。本文综述了近年来砷及其形态常用的测定方法,并且分析了各检测方法的优缺点,展望了砷及其形态检测技术的发展前景。      

Determination of total arsenic content and arsenic speciation in different types of rice

Food Science and Biotechnology - The objectives of this study was to examine the amount of total arsenic and arsenic speciation in different types of rice from two areas in Korea using inductively...     

Variation in arsenic speciation and concentration in paddy rice related to dietary exposure

Ingestion of drinking water is not the only elevated source of arsenic to the diet in the Bengal Delta. Even at background levels, the arsenic in rice contributes considerably to arsenic ingestion in subsistence rice diets. We set out to survey As speciation in different rice varieties from different parts of the globe to understand the contribution of rice to arsenic exposure. Pot experiments were utilized to ascertain whether growing rice on As contaminated soil affected speciation and whether genetic variation accounted for uptake and speciation. USA long grain rice had the highest mean arsenic level in the grain at 0.26 microg As g(-1) (n = 7), and the highest grain arsenic value of the survey at 0.40 microg As g(-1). The mean arsenic level of Bangladeshi rice was 0.13 microg As g(-1) (n = 15). The main As species detected in the rice extract were AsIII, DMAV, and AsV. In European, Bangladeshi, and Indian rice 64 +/- 1% (n = 7), 80 +/- 3% (n = 11), and 81 +/- 4% (n = 15), respectively, of the recovered arsenic was found to be inorganic. In contrast, DMAV was the predominant species in rice from the USA, with only 42 +/- 5% (n = 12) of the arsenic being inorganic. Pot experiments show that the proportions of DMAV in the grain are significantly dependent on rice cultivar (p = 0.026) and that plant nutrient status is effected by arsenic exposure.     

食品中砷的形态分析研究进展

砷是一种公认的有毒有害物质,现在相关研究中常涉及的砷形态包括亚砷酸盐(arsenite,AsⅢ)、砷酸盐(arsenate,AsⅤ)、一甲基砷酸(monomethyl arsenic acid,MMAⅤ)、二甲基砷酸(dimethyl arsinic acid,DMAⅤ)、砷甜菜碱(arsenobetaine,AsB)以及砷胆碱(arsenocholine,AsC)。砷的形态与其生物可给性、毒性密切相关,烹调过程能够影响食品中砷的形态,进而可能影响到砷对人体健康的风险性。因此,建立食品中砷形态分析的检测方法具有十分重要的意义。本文对砷的形态分析的检测方法及研究现状进行了综述,重点介绍了溶剂提取及微波、超声辅助提取等前处理方法以及砷的形态分析方法在食品中的应用,同时对砷的形态在烹调过程中的变化进行了阐述,并对未来发展方向进行了展望。     

XAS speciation of arsenic in a hyper-accumulating fern

The coordination environment and the redox speciation of arsenic in a newly discovered arsenic hyper-accumulating fern (Pteris vittata L) were investigated by X-ray absorption spectroscopy. This method allowed us to probe arsenic directly, i.e., with minimal sample preparation. The results indicate that arsenic is predominantly accumulated as As(III) in the leaves. XANES and EXAFS results show that As(III) in the leaves is primarily present as aqueous arsenite species. The plant actively maintains arsenic in this reduced oxidation state, because after sample collection and subsequent aging and drying of the plant material, As(III) is gradually oxidized to As(V). We think that these arsenite species are sequestered in vacuoles. At extremely high As concentrations (ca. 1% As per dry weight) arsenic in the fern leaves is coordinated to a significant degree by sulfur in addition to oxygen. This spectral signature indicates that thiol-rich compounds are implicated in the biochemical transformations of arsenic within the plant.     

A novel technique to determine cobalt exchangeability in soils using isotope dilution

The environmental risk posed by Co contamination is largely a function of its oxidation state. Our objective was to assess the potential biological availability of Co and the reactions and fate of soluble Co(II) after addition to soils with varying physical and chemical characteristics. A potential risk in quantifying exchangeable Co in soils using isotope dilution techniques is the possible presence of two species of Co in soil solution and adsorbed on soil solid phases [Co(II) and Co(III)], coupled with the possibility that when an isotope of Co is added it may undergo a change in oxidation state during the measurement phase. In this study, we have utilized an isotope dilution technique with cation exchange and high-performance liquid chromatography-inductively coupled plasma-mass spectrometry to determine the isotopically exchangeable Co fraction in several soils with varying characteristics such as differing Al, Fe, and Mn oxide content; pH; and organic carbon content. The application of the cation exchange procedure adjusts measurements of isotopically exchangeable Co to correct for the presence of non-exchangeable 57Co not in equilibrium with the solution phase. Results indicated that oxidation of added 57Co(II) to 57Co(III) or precipitation of 57Co(II) may occur on the surfaces of some soils, particularly those with a high pH or substantial quantities of Mn oxide minerals. No detectable Co(III)(aq) was found in the aqueous extracts of the soils examined.     

海产品中砷形态分析研究进展

我国是海产品的生产和消费大国,所以海产品的安全问题受到人们越来越多的关注。海产品特别是食用海藻含砷量较高,但是海产品中的砷大部分以低毒性的有机砷形态存在,而且不同种类的海产品所含有的砷形态各不相同。所以,对海产品中的不同形态砷化合物进行精准分析检测,对于科学、客观评估海产品中砷污染的健康风险以及保证海产品的安全消费具有重要意义。海产品的砷形态分析面临的困难主要是,第一在不改变砷形态的前提下把海产品中所有形态砷化合物完全提取出来;第二把各形态有机砷和无机砷在较短时间内实现基线分离、并对各形态砷化合物进行高灵敏检测。近十多年来,有关海产品中砷的形态分析得到越来越多的关注,在方法学上也取得了显著的进步。本文主要针对近十多年来有关不同海产品中不同形态砷化合物的提取方法和分析检测方法方面的研究进展进行了概述,以期为食品检测机构或食品安全研究或评估人员提供方法学上的参考。     

Modeling the effect of algal dynamics on arsenic speciation in Lake Biwa

Algae reduce and methylate arsenate and the end product of the reaction is correlated to their growth rate. At slow growth rates, dimethylarsinate (DMA) is produced, and at fast growth rates arsenite (As(III)) is produced. Previous work has linked this phenomenon to the phosphorus luxury uptake mechanism of algae, and a model was developed for the process (Hellweger et al. Limnol. Oceanogr. 2003, 48, 2275). This paper presents the integration of that process model for arsenic transformation by algae into a full ecological model and application to Lake Biwa, Japan. The model application allows for a quantitative analysis of the field data, consistent with the process model and the ecological dynamics of the lake. The newly developed ecological model includes a variable phytoplankton composition, which is needed to simulate luxury uptake. This is in contrast to most existing ecological models, which typically assume a fixed "Redfield" composition. The model adequately reproduces the observed ecology of Lake Biwa, including the rapid uptake of phosphate by phytoplankton without immediate growth (luxury uptake) following lake overturn. The model also reproduces the observed arsenic speciation, including the gradual appearance of DMA during the summer and peaks in As(III) concentration at the onset of spring and fall algal blooms.     

Natural organic matter affects arsenic speciation and sorption onto hematite

Arsenic mobility in natural environments is controlled primarily by sorption onto metal oxide surfaces, and the extent of this sorption may be influenced strongly by the presence of other dissolved substances that interact with surfaces or with arsenic itself. Natural organic matter (NOM), a prevalent constituent of natural waters, is highly reactive toward both metals and surfaces and is thus a clear candidate to influence arsenic mobility. The objectives of this study were therefore to reveal the influences of diverse NOM samples on the sorption of arsenic onto hematite, a model metal oxide, as well as to reveal influences of arsenic on the sorption of NOM, using conditions and concentrations relevant to natural freshwater environments. Of the six NOM samples tested, four formed aqueous complexes with arsenate and arsenite. The extent of complexation varied with the NOM origin and, in particular, increased with the cationic metal (primarily Fe) content of the NOM sample. In addition, every NOM sample showed active redox behavior toward arsenic species, indicating that NOM may greatly influence redox as well as complexation speciation of arsenic in freshwater environments. When NOM and As were incubated together with hematite, NOM dramatically delayed the attainment of sorption equilibrium and diminished the extent of sorption of both arsenate and arsenite. Consistent with this result, when NOM and As were introduced sequentially, all NOM samples displaced sorbed arsenate and arsenite from hematite surfaces, and arsenic species similarly displaced sorbed NOM from hematite in significant quantities. Competition between NOM and As for sorption thus appears to be a potentially important process in natural waters, suggesting that NOM may play a greater role in arsenic mobility than previously recognized. In addition, in all sorption experiments, arsenite was consistently desorbed or prevented from sorbing to a greater extent than arsenate, indicating that interactions with NOM may also partially explain the generally greater mobility of arsenite in natural environments.