Showing papers on "Arsenic published in 2008"

Transporters of arsenite in rice and their role in arsenic accumulation in rice grain

Abstract: Arsenic poisoning affects millions of people worldwide. Human arsenic intake from rice consumption can be substantial because rice is particularly efficient in assimilating arsenic from paddy soils, although the mechanism has not been elucidated. Here we report that two different types of transporters mediate transport of arsenite, the predominant form of arsenic in paddy soil, from the external medium to the xylem. Transporters belonging to the NIP subfamily of aquaporins in rice are permeable to arsenite but not to arsenate. Mutation in OsNIP2;1 (Lsi1, a silicon influx transporter) significantly decreases arsenite uptake. Furthermore, in the rice mutants defective in the silicon efflux transporter Lsi2, arsenite transport to the xylem and accumulation in shoots and grain decreased greatly. Mutation in Lsi2 had a much greater impact on arsenic accumulation in shoots and grain in field-grown rice than Lsi1. Arsenite transport in rice roots therefore shares the same highly efficient pathway as silicon, which explains why rice is efficient in arsenic accumulation. Our results provide insight into the uptake mechanism of arsenite in rice and strategies for reducing arsenic accumulation in grain for enhanced food safety.

Growing Rice Aerobically Markedly Decreases Arsenic Accumulation

Abstract: Arsenic (As) exposure from consumption of rice can be substantial, particularly for the population on a subsistence rice diet in South Asia. Paddy rice has a much enhanced As accumulation compared with other cereal crops, and practical measures are urgently needed to decrease As transfer from soil to grain. We investigated the dynamics of As speciation in the soil solution under both flooded and aerobic conditions and compared As accumulation in rice shoot and grain in a greenhouse experiment. Flooding of soil led to a rapid mobilization of As, mainly as arsenite, in the soil solution. Arsenic concentrations in the soil solution were 7−16 and 4−13 times higher under the flooded than under the aerobic conditions in the control without As addition and in the +As treatments (10 mg As kg−1 as arsenite or arsenate), respectively. Arsenate was the main As species in the aerobic soil. Arsenic accumulation in rice shoots and grain was markedly increased under flooded conditions; grain As concentrations were 10−15...

Arsenic and Arsenic Compounds

Abstract: The article contains sections titled: 1. Arsenic 1.1. Introduction 1.2. Physical Properties 1.3. Chemical Properties 1.4. Occurrence 1.5. Production 1.5.1. Production of Arsenic Trioxide 1.5.1.1. Ore Dressing 1.5.1.2. Pretreatment of Arsenical Materials 1.5.1.2.1. Roasting 1.5.1.2.2. Alternative Pretreatments of Arsenical Materials 1.5.1.3. Production of Refined As2O3 1.5.2. Production of the Metal 1.6. Treatment of Arsenic-Containing Byproducts 2. Arsenic Compounds 2.1. Arsenic Trioxide 2.2. Arsenous Acid 2.3. Arsenic Pentoxide 2.4. Arsenic Acid 2.5. Arsenic Sulfides 2.6. Arsenic Halides 2.7. Arsenic Hydride and Arsenides 2.8. Organoarsenic Compounds 2.8.1. Aliphatic Organoarsenic Compounds 2.8.2. Aromatic Organoarsenic Compounds 3. Uses and Economic Aspects 4. Stabilization of Arsenic for Safe Disposal 5. Recycling 6. Safety Measures 7. Toxicology

Near-Surface Wetland Sediments as a Source of Arsenic Release to Ground Water in Asia

Abstract: Tens of millions of people in south and southeast Asia routinely consume ground water that has unsafe arsenic levels. Arsenic is naturally derived from eroded Himalayan sediments, and is believed to enter solution following reductive release from solid phases under anaerobic conditions. However, the processes governing aqueous concentrations and locations of arsenic release to pore water remain unresolved, limiting our ability to predict arsenic concentrations spatially (between wells) and temporally (future concentrations) and to assess the impact of human activities on the arsenic problem. This uncertainty is partly attributed to a poor understanding of groundwater flow paths altered by extensive irrigation pumping in the Ganges-Brahmaputra delta, where most research has focused. Here, using hydrologic and (bio)geochemical measurements, we show that on the minimally disturbed Mekong delta of Cambodia, arsenic is released from near-surface, river-derived sediments and transported, on a centennial timescale, through the underlying aquifer back to the river. Owing to similarities in geologic deposition, aquifer source rock and regional hydrologic gradients, our results represent a model for understanding pre-disturbance conditions for other major deltas in Asia. Furthermore, the observation of strong hydrologic influence on arsenic behaviour indicates that release and transport of arsenic are sensitive to continuing and impending anthropogenic disturbances. In particular, groundwater pumping for irrigation, changes in agricultural practices, sediment excavation, levee construction and upstream dam installations will alter the hydraulic regime and/or arsenic source material and, by extension, influence groundwater arsenic concentrations and the future of this health problem.

Statistical Modeling of Global Geogenic Arsenic Contamination in Groundwater

Abstract: Contamination of groundwaters with geogenic arsenic poses a major health risk to millions of people. Although the main geochemical mechanisms of arsenic mobilization are well understood, the worldwide scale of affected regions is still unknown. In this study we used a large database of measured arsenic concentration in groundwaters (around 20,000 data points) from around the world as well as digital maps of physical characteristics such as soil, geology, climate, and elevation to model probability maps of global arsenic contamination. A novel rule-based statistical procedure was used to combine the physical data and expert knowledge to delineate two process regions for arsenic mobilization: “reducing” and “high-pH/oxidizing”. Arsenic concentrations were modeled in each region using regression analysis and adaptive neuro-fuzzy inferencing followed by Latin hypercube sampling for uncertainty propagation to produce probability maps. The derived global arsenic models could benefit from more accurate geologic ...

Speciation and Localization of Arsenic in White and Brown Rice Grains

Abstract: Synchrotron-based X-ray fluorescence (S-XRF) was utilized to locate arsenic (As) in polished (white) and unpolished (brown) rice grains from the United States, China, and Bangladesh. In white rice As was generally dispersed throughout the grain, the bulk of which constitutes the endosperm. In brown rice As was found to be preferentially localized at the surface, in the region corresponding to the pericarp and aleurone layer. Copper, iron, manganese, and zinc localization followed that of arsenic in brown rice, while the location for cadmium and nickel was distinctly different, showing relatively even distribution throughout the endosperm. The localization of As in the outer grain of brown rice was confirmed by laser ablation ICP-MS. Arsenic speciation of all grains using spatially resolved X-ray absorption near edge structure (micro-XANES) and bulk extraction followed by anion exchange HPLC-ICP-MS revealed the presence of mainly inorganic As and dimethylarsinic acid (DMA). However, the two techniques indicated different proportions of inorganic:organic As species. A wider survey of whole grain speciation of white (n=39) and brown (n=45) rice samples from numerous sources (field collected, supermarket survey, and pot trials) showed that brown rice had a higher proportion of inorganic arsenic present than white rice. Furthermore, the percentage of DMA present in the grain increased along with total grain arsenic.

Arsenic pollution sources.

Abstract: Arsenic is a widely dispersed element in the Earth's crust and exists at an average concentration of approximately 5 mg/kg. There are many possible routes of human exposure to arsenic from both natural and anthropogenic sources. Arsenic occurs as a constituent in more than 200 minerals, although it primarily exists as arsenopyrite and as a constituent in several other sulfide minerals. The introduction of arsenic into drinking water can occur as a result of its natural geological presence in local bedrock. Arsenic-containing bedrock formations of this sort are known in Bangladesh, West Bengal (India), and regions of China, and many cases of endemic contamination by arsenic with serious consequences to human health are known from these areas. Significant natural contamination of surface waters and soil can arise when arsenic-rich geothermal fluids come into contact with surface waters. When humans are implicated in causing or exacerbating arsenic pollution, the cause can almost always be traced to mining or mining-related activities. Arsenic exists in many oxidation states, with arsenic (III) and (V) being the most common forms. Similar to many metalloids, the prevalence of particular species of arsenic depends greatly on the pH and redox conditions of the matrix in which it exists. Speciation is also important in determining the toxicity of arsenic. Arsenic minerals exist in the environment principally as sulfides, oxides, and phosphates. In igneous rocks, only those of volcanic origin are implicated in high aqueous arsenic concentrations. Sedimentary rocks tend not to bear high arsenic loads, and common matrices such as sands and sandstones contain lower concentrations owing to the dominance of quartz and feldspars. Groundwater contamination by arsenic arises from sources of arsenopyrite, base metal sulfides, realgar and orpiment, arsenic-rich pyrite, and iron oxyhydroxide. Mechanisms by which arsenic is released from minerals are varied and are accounted for by many (bio)geochemical processes: oxidation of arsenic-bearing sulfides, desorption from oxides and hydroxides, reductive dissolution, evaporative concentration, leaching from sulfides by carbonate, and microbial mobilization. Arsenic enrichment also takes place in geothermally active areas; surface waters are more susceptible than groundwater to contamination in the vicinity of such geothermal systems, and evidence suggests that increased use of geothermal power may elevate risks of arsenic exposure in affected areas. Past and current mining activities continue to provide sources of environmental contamination by arsenic. Because gold- and arsenic-bearing minerals coexist, there is a hazard of mobilizing arsenic during gold mining activities. The Ashanti region of central Ghana currently faces this as a real risk. Historical arsenic contamination exists in Cornwall, UK; an example of a recent arsenic pollution event is that of Ron Phibun town in southern Thailand, where arsenic-related human health effects have been reported. Other important sources of arsenic exposure include coal burning in Slovakia, Turkey, and the Guizhou Province of China; use of arsenic as pesticides in Australia, New Zealand, and the US; and consumption of contaminated foodstuffs (China) and exposure to wood preserving arsenicals (Europe and North America).

Surface-enhanced Raman spectroscopy for trace arsenic detection in contaminated water.

Abstract: Low-level arsenic contamination of drinking water in Bangladesh, India, and parts of China presents an international public health crisis, with over 300000 deaths attributed to chronic poisoning in Bangladesh alone. In 1993, the World Health Organization set a provisional guideline of 10 ppb (0.01 mgL ) for maximum arsenic content in groundwater. However, exposure to arsenic at these concentrations still results in increased rates of skin, lung, urinary bladder, and kidney cancer. New technologies allowing reliable detection of arsenic below 10 ppb should instigate a stricter standard. Current technologies for laboratory analysis (e.g. inductively coupled plasma (ICP) MS, atomic fluorescence spectroscopy (AFS), HPLC-MS) allow detection at these levels, but they are neither readily available in developing countries nor capable of on-site field detection. The current state of field-compatible technologies has been reviewed, and there remains significant room for improvement. Even if current chemical field tests are improved to meet these standards, there are no examples of chemical indicators that can distinguish the oxidation state of the arsenic species. For exposure studies, this knowledge is necessary for toxicology, remediation, and monitoring of the effects within the local populations. By developing a highly active substrate for surface-enhanced Raman spectroscopy (SERS) that can be used in conjunction with portable Raman technology, many of these challenges can be surmounted. Since the discovery of SERS in the late 1970s there has been a continual push to maximize the Raman signal for molecules near nanostructured surfaces. SERS enhancement results from an intense local amplification of the electric field near a metal surface when collective oscillations of conduction electrons resonate in phase with the incident light. The size, shape, and proximity of nanostructures all affect the frequency and magnitude of the localized surface plasmons (LSPs), thus directly influencing the degree of Raman enhancement exhibited. LSPs have been directly observed using experimental techniques such as scanning near field and TEM-correlated dark field microscopy. These experiments, along with more conventional light-scattering techniques, demonstrate the dramatic effects that size and shape have on the LSPs. Recent studies on electromagnetic coupling between nanostructures that are nearly touching indicate that such collective effects can excite LSPs that lead to even higher electromagnetic enhancement. Although it is widely known that silver shows the strongest plasmonic response, gold is often used for sensing applications because of its chemical stability and compatibility with many laser excitation wavelengths. For our SERS sensor, we have introduced two key features that lead to better analytical capability under typical sensing conditions. First, dense arrays of silver nanocrystals are fabricated using Langmuir–Blodgett (LB) assembly. These close-packed monolayers exhibit broadband scattering profiles, making them compatible with many different excitation wavelengths. The second key feature is the surface passivation of the silver particles with adsorbed polymer. Surface-adsorbed poly(vinyl pyrrolidone) (PVP) serves dual purposes: it functions as the passivating ligand during nanocrystal synthesis, and it stabilizes the silver particles to oxidation while still facilitating interaction between silver and arsenate during sensing experiments. The PVP coating makes these silver nanostructures airand water-stable over much longer periods then other passivating ligands. The synthesis of the polyhedral silver nanoparticles proceeds by the polyol process, in which the metal-salt precursors and a polymer capping agent (PVP) are alternately added to a solution of pentanediol heated near reflux. In this way the pentanediol acts as both the solvent and the reductant for the reaction, while PVP imparts shape control as the particles grow. The final shape of the particles is dictated by the length of the reaction; the particles are progressively capped by more [111] faces (see Figure 1). This growth results in an increase of the particle size as the reaction progresses, starting with cubes which are 80–100 nm on an edge, then cuboctahedra with diameters of 150–200 nm, and finally octahedra with edge lengths of 250–300 nm. Typically these nanocrystals can be isolated as nearly monodisperse suspensions, and final purification is achieved by filtration through 0.45-mm Durapore filters. Homogeneity of [*] M. Mulvihill, K. Benjauthrit, Prof. J. Arnold, Prof. P. Yang Department of Chemistry University of California, Berkeley Berkeley, CA 94720 (USA) Fax: (+1)510-642-7301 E-mail: p_yang@berkeley.edu

Inorganic Arsenic in Rice Bran and Its Products Are an Order of Magnitude Higher than in Bulk Grain

Abstract: Rice is more elevated in arsenic than all other grain crops tested to date, with whole grain (brown) rice having higher arsenic levels than polished (white). It is reported here that rice bran, both commercially purchased and specifically milled for this study, have levels of inorganic arsenic, a nonthreshold, class 1 carcinogen, reaching concentrations of approximately 1 mg/kg dry weight, around 10-20 fold higher than concentrations found in bulk grain. Although pure rice bran is used as a health food supplement, perhaps of more concern is rice bran solubles, which are marketed as a superfood and as a supplement to malnourished children in international aid programs. Five rice bran solubles products were tested, sourced from the United States and Japan, and were found to have 0.61-1.9 mg/kg inorganic arsenic. Manufactures recommend approximately 20 g servings of the rice bran solubles per day, which equates to a 0.012-0.038 mg intake of inorganic arsenic. There are no maximum concentration levels (MCLs) set for arsenic or its species in food stuffs. EU and U.S. water regulations, set at 0.01 mg/L total or inorganic arsenic, respectively, are based on the assumption that 1 L of water per day is consumed, i.e., 0.01 mg of arsenic/ day. At the manufacturers recommended rice bran solubles consumption rate, inorganic arsenic intake exceeds 0.01 mg/ day, remembering that rice bran solubles are targeted at malnourished children and that actual risk is based on mg kg(-1) day(-1) intake.

Health effects of early life exposure to arsenic

Abstract: Inorganic arsenic is a potent human carcinogen and general toxicant. More than one hundred million people are exposed to elevated concentrations, mainly via drinking water, but also via industrial emissions. Arsenic is metabolized via methylation and reduction reactions, methylarsonic acid and dimethylarsinic acid being the main metabolites excreted in urine. Both inorganic arsenic and its methylated metabolites easily pass the placenta and both experimental and human studies have shown increased risk of impaired foetal growth and increased foetal loss. Recent studies indicate that prenatal arsenic exposure also increases the risk of adverse effects during early childhood. There is a growing body of evidence that the intrauterine or early childhood exposure to arsenic also induces changes that will become apparent much later in life. One epidemiological study indicated that exposure to arsenic in drinking water during early childhood or in utero was associated with an increased mortality in young adults from both malignant and non-malignant lung disease. Furthermore, a series of experimental animal studies provide strong support for late effects of arsenic, including various forms of cancer, following intrauterine arsenic exposure. The involved modes of action include epigenetic effects, mainly via DNA hypomethylation, endocrine effects (most classes of steroid hormones), immune suppression, neurotoxicity, and interaction with enzymes critical for foetal development and programming.

Arsenic in rice: II. Arsenic speciation in USA grain and implications for human health.

Abstract: Rice is a potentially important route of human exposure to arsenic, especially in populations with rice-based diets. However, arsenic toxicity varies greatly with species. The initial purpose of the present study was to evaluate arsenic speciation in U.S. rice. Twenty-four samples containing high levels of arsenic and produced in different regions of the U.S were selected from a previous market-basket survey. Arsenite and dimethyl arsinic acid (DMA) were the major species detected. DMA increased linearly with increasing total As but arsenite remained fairly constant at ∼0.1 mg kg−1, showing that rice high in As was dominated by DMA. A similar result was obtained when our data was combined with other published speciation studies for U.S. rice. However, when all published speciation data for rice was analyzed a second population dominated by inorganic As and lower levels of DMA was found. We thus categorized rice into DMA and Inorganic As types. Rice from the U.S. was predominantly the DMA type, as were sin...

Comparative proteomic study of arsenic‐induced differentially expressed proteins in rice roots reveals glutathione plays a central role during As stress

Abstract: While the phytotoxic responses of arsenic (As) on plants have been studied extensively, based on physiological and biochemical aspects, very little is known about As stress-elicited changes in plants at the proteome level. Hydroponically grown 2-wk-old rice seedlings were exposed to different doses of arsenate, and roots were collected after 4 days of treatment, as well as after a recovery period. To gain a comprehensive understanding of the precise mechanisms underlying As toxicity, metabolism, and the defense reactions in plants, a comparative proteomic analysis of rice roots has been conducted in combination with physiological and biochemical analyses. Arsenic treatment resulted in increases of As accumulation, lipid peroxidation, and in vivo H2O2 contents in roots. A total of 23 As-regulated proteins including predicted and novel ones were identified using 2-DE coupled with MS analyses. The expression levels of S-adenosylmethionine synthetase (SAMS), GSTs, cysteine synthase (CS), GST-tau, and tyrosine-specific protein phosphatase proteins (TSPP) were markedly up-regulated in response to arsenate, whereas treatment by H2O2 also regulated the levels of CS suggesting that its expression was certainly regulated by As or As-induced oxidative stress. In addition, an omega domain containing GST was induced only by arsenate. However, it was not altered by treatment of arsenite, copper, or aluminum, suggesting that it may play a particular role in arsenate stress. Analysis of the total glutathione (GSH) content and enzymatic activity of glutathione reductase (GR) in rice roots during As stress revealed that their activities respond in a dose-dependent manner of As. These results suggest that SAMS, CS, GSTs, and GR presumably work synchronously wherein GSH plays a central role in protecting cells against As stress.

Mineral arsenicals in traditional medicines: orpiment, realgar, and arsenolite

Abstract: Mineral arsenicals have long been used in traditional medicines for various diseases, yet arsenic can be highly toxic and carcinogenic. Arsenic in traditional medicines typically comes from deliberate addition for therapeutic purposes, mainly in the form of mineral arsenicals, including orpiment (As2S3), realgar (As4S4), and arsenolite (contains arsenic trioxide, As2O3). Inorganic arsenic is now accepted in Western medicine as a first line chemotherapeutic agent against certain hematopoietic cancers. This perspective analyzes the pharmacology and toxicology of these arsenicals used in traditional medicines. Orpiment and realgar are less soluble and poorly absorbed from the gastrointestinal tract, whereas the bioavailability of arsenic trioxide is similar to inorganic arsenic salts such as sodium arsenite. Pharmacological studies show that arsenic trioxide and realgar are effective against certain malignancies. Orpiment and realgar are used externally for various skin diseases. Realgar is frequently included as an ingredient in oral traditional remedies for its antipyretic, anti-inflammatory, antiulcer, anti-convulsive, and anti-schistosomiasis actions, but the pharmacological basis for this inclusion still remains to be fully justified. Toxicological studies show that cardiovascular toxicity is the major concern for arsenic trioxide and that the gastrointestinal and dermal adverse effects may occur after prolonged use of mineral arsenicals. Little is known regarding the possible secondary cancers resulting from the long-term use of any of these arsenicals. Similar to the safety evaluation of seafood arsenicals, total arsenic content alone appears to be insufficient for mineral arsenical safety evaluation. Arsenic speciation, bioavailability, and toxicity/benefit should be considered in evaluation of mineral arsenical-containing traditional medicines.

Preloading hydrous ferric oxide into granular activated carbon for arsenic removal.

Abstract: Arsenic is of concern in water treatment because of its health effects. This research focused on incorporating hydrous ferric oxide (HFO) into granular activated carbon (GAC) for the purpose of arsenic removal. Iron was incorporated into GAC via incipient wetness impregnation and cured at temperatures ranging from 60 to 90 degrees C. X-ray diffractions and arsenic sorption as a function of pH were conducted to investigate the effect of temperature on final iron oxide (hydroxide) and their arsenic removal capabilities. Results revealed that when curing at 60 degrees C, the procedure successfully created HFO in the pores of GAC, whereas at temperatures of 80 and 90 degrees C, the impregnated iron oxide manifested a more crystalline form. In the column tests using synthetic water, the HFO-loaded GAC prepared at 60 degrees C also showed higher sorption capacities than media cured at higher temperatures. These results indicated that the adsorption capacity for arsenic was closely related to the form of iron (hydr)oxide for a given iron content For the column test using a natural groundwater, HFO-loaded GAC (Fe, 11.7%) showed an arsenic sorption capacity of 26 mg As/g when the influent contained 300 microg/L As. Thus, the preloading of HFO into a stable GAC media offered the opportunity to employ fixed carbon bed reactors in water treatment plants or point-of-use filters for arsenic removal.

Individual and competitive adsorption of arsenate and phosphate to a high-surface-area iron oxide-based sorbent.

Abstract: Individual and competitive adsorption of arsenate and phosphate were studied on a high-surface-area Fe/Mn-(hydr)oxide sorbent with surface and bulk properties similar to those of two-line ferrihydrite. It has maximum adsorption densities of 0.42 µmol As m−2 at neutral pH and 1.24 µmol As m−2 at pH 3. A surface complexation model (SCM) that used the diffuse double layer model was developed that could simulate single and binary sorbate adsorption over pH 4–9. The predominant adsorbed arsenate and phosphate species were modeled as bidentate binuclear surface complexes at low pH and as monodentate complexes at high pH. The model initially overpredicted the inhibition of arsenate adsorption by the presence of phosphate. The overprediction was resolved by separating surface sites into two types: ones to which both arsenate and phosphate bind and a smaller number to which only phosphate binds. The modified model predicted the competitive adsorption of arsenate and phosphate over pH 4–9 at total As concentrations...

Sedimentary arsenite-oxidizing and arsenate-reducing bacteria associated with high arsenic groundwater from Shanyin, Northwestern China.

Abstract: Aims: Shanyin County is one of the most severe endemic arsenism affected areas in China but micro-organisms that potentially release arsenic from sediments to groundwater have not been studied. Our aim was to identify bacteria with the potential to metabolize or transform arsenic in the sediments. Methods and Results: Culture and nonculture-based molecular methods were performed to identify arsenite-oxidizing bacteria, arsenate-reducing bacteria and arsenite oxidase genes. Arsenite-oxidizing bacteria were identified only from the land surface to 7 m underground that were affiliated to α- and β-Proteobacteria. Arsenate-reducing bacteria were found in almost all the sediment samples with different depths (0–41 m) and mainly belong to γ-Proteobacteria. Several novel arsenite oxidase genes (aoxBs) were identified from the upper layers of the sediments (0–7 m) and were found to be specific for arsenite-oxidizing bacteria. Conclusions: The distribution of arsenite-oxidizing bacteria in upper layers and arsenate-reducing bacteria in different depths of the sediments may impact the arsenic release into the nearby tubewell groundwater. Significance and Impact of the Study: This study provides valuable sources of micro-organisms (and genes) that may contribute to groundwater arsenic abnormality and may be useful to clean arsenic contaminated groundwater.