Arsenic Absorption Research Articles

Effects of dissolution kinetics on bioaccessible arsenic from tailings and soils

Dissolution kinetics of arsenic from soils and tailings were studied under simulated gastrointestinal conditions to determine the effects of residence time, pH and soil composition on the bioaccessibility of arsenic. The samples were sieved to four particle size fractions from bulk to <45 μm, and included arsenic minerals, soils and tailings with total arsenic concentrations ranging from 19 to 420 00 mg kg −1. The bioaccessible arsenic concentrations varied from 2.8 to 10 000 mg kg −1, and the highest concentrations were associated with the smallest particle size fractions. Kinetic parameters were determined for each sample extracted under gastric conditions (pH = 1.8) followed by intestinal conditions (pH = 7.0). Under gastric pH conditions, dissolution appeared to be diffusion-controlled and followed an exponential curve, whereas a logarithmic or linear model was used to describe the mixed dissolution mechanisms observed under intestinal conditions. Nine of the 13 samples tested reached a steady state bioaccessible arsenic concentration within the 5-h physiologically-based extraction test (PBET). However the bioaccessible arsenic concentrations in four tailings samples increased significantly ( p = 0.034) between the 5-h and the extended 24-h extraction under intestinal conditions. Since arsenic absorption may occur along the entire digestive tract, assessments based on the standard 5-h PBET extraction may not adequately estimate the risks associated with arsenic absorption in such cases. The slow dissolution kinetics associated with secondary arsenic minerals in some tailings samples may require extending the PBET extractions to longer periods, or extrapolating using the proposed kinetic models, to reach steady state concentrations in simulated gastrointestinal fluids.

Efficiency and Effects of Chemical Chelants Leaching on Arsenical Gold Mine Pretreatment by &lt;i&gt;Pteris vittata&lt;/i&gt; L. in Arsenical Gold Ore

Using pot experiment, the total arsenic absorbed by Pteris vittata L.from gold roe collected from Guizhou Xingren gold mine was investigated. Arsenic extraction efficiency and effects by five kinds of chelants such as Ethylene diamine tetraacetic acid disodium salt (EDTA-Na2), citric acid (CA), ammonium dihydrogen phosphate (MAP), Sodium bisulfite (NaHSO3) and Sodium bicarbonate (NaHCO3) were assessed. Absorption of As was measured in the fronds and roots of Pteris vittata L.under pot trial condition in which the tested gold ore powder was leached by the above five chelants with the concentrations of 0, 0.05, 0.1 and 0.15 mol•L-1, respectively. The results show that most of the chosen chelants can largely improve the efficiency of arsenic absorption. The leaching efficiency of As in fronds was generally listed in the following order: MAP&gt;EDTA-Na2&gt;CA&gt;NaHCO3&gt;NaHSO3 under the average concentration．With the increase of chelant concentration the As was extracted more and more on MAP and NaHCO3 . The extracting content of As ranged from 5055ug/g to 5974ug/g for EDTA, from3273 ug/g to 4975 ug/g for CA, from 7482 ug/g to 9357 ug/g for MAP and from 3620 ug/g to 5284 ug/g for NaHSO3, from 3401 ug/g to 6378 ug/g for NaHCO3, respectively. The leaching efficiency of As in roots was generally listed in the following order: MAP&gt; NaHCO3&gt;NaHSO3&gt;EDTA-Na2&gt;CA under the average concentration．The extracting content of As ranged from 1862ug/g to 2627ug/g for EDTA, from1494 ug/g to 2347 ug/g for CA, from 2739 ug/g to 3896 ug/g for MAP and from 2064 ug/g to 3373 ug/g for NaHSO3, from 2316 ug/g to 2587 ug/g for NaHCO3, respectively. These results mentioned above show that available As in Guizhou xingren gold mine can be most leached by Pteris vittata L.with the above chelants, especially in MAP treatment. MAP was the best chelants among the four tested chelants, suggesting that it will be useful in chelant-induced phyto-remediation.

Arsenic removal from water by magnetic Fe1− x Co x Fe2O4 and Fe1− y Ni y Fe2O4 nanoparticles

This article studies the effects of Co and Ni replacement in Fe1− x Co x Fe2O4 and Fe1− y Ni y Fe2O4 (x, y = 0, 0.05, 0.1, 0.2, 0.5) nanoparticles, pH, weight of nanoparticles/mL of water, and time of stirring on the arsenic removal ability. The results showed that a small amount (0.25 g L−1) of Fe3O4 nanoparticles after stirring time of 3 min can reduce the arsenic concentration from 0.1 to 0.01 mg L−1. The removal was also affected by the pH of the water. Absorption of arsenic by nanoparticles was effective when pH was smaller than seven and reduced with the increase of pH. At pH of 13, there was a strong release of arsenic ions from arsenic-absorbed nanoparticles back to water. The time of stirring was studied from 1 min to 2 h and the optimal time was about few minutes. Co and Ni's presence was reported to keep saturation magnetisation stable under working conditions. For Co replacement, absorption does not change significantly when x ≤ 0.1 and slightly reduces when x > 0.1. The presence of Ni improved the absorption in most cases.

Potencial de quatro espécies herbáceas forrageiras para fitorremediação de solo contaminado por arsênio

A fitorremediação de solos e substratos contaminados por elementos tóxicos tem despertado crescente interesse entre pesquisadores e técnicos. Particularmente em relação ao As, o obstáculo ao emprego desta técnica é o pequeno número de espécies identificadas capazes de acumular este elemento. O objetivo deste trabalho foi avaliar o potencial de plantas de estilosante (Stylosanthes humilis HBK), amendoim (Arachis pintoi Krapov. &amp; Gregory), aveia (Avena strigosa Schreb) e azevém (Lolium multiflorum Lam.) como espécies fitorremediadoras de áreas contaminadas por As. Amostras de Latossolo Vermelho-Amarelo foram incubadas por 15 dias com diferentes doses de As: 0; 50; 100; e 200 mg dm-3. Em seguida, realizaram-se a semeadura das quatro espécies e as respectivas adubações. Aos 65 dias após a semeadura, as plantas foram avaliadas quanto à altura, à matéria seca da parte aérea e raízes. Determinaram-se os teores de As nas folhas jovens, intermediárias e basais, no caule e nas raízes, bem como o conteúdo e o índice de translocação (IT) de As. Por meio de análises de regressão, foram estimados os teores críticos (TC) de As disponíveis no solo, que proporcionaram redução de 50 % da matéria seca. As espécies estudadas apresentaram comportamento diferenciado quanto à tolerância ao As, com destaque para azevém, amendoim e estilosante, que não apresentaram lesões foliares decorrentes de fitotoxidez por esse elemento. Os TC para as plantas de aveia e azevém foram significativamente superiores aos observados para as demais espécies, caracterizando-as como espécies tolerantes ao As. As plantas de amendoim e estilosante apresentaram maior capacidade de absorção e maior IT de As para a parte aérea. As plantas de amendoim apresentaram maiores teores nas folhas basais e raízes, mostrando potencial para serem utilizadas em programas de fitorremediação. As plantas de azevém, amendoim e estilosante podem ser utilizadas na fitoestabilização e, ou, na revegetação de áreas contaminadas por As, uma vez que apresentaram tolerância a esse elemento. Por se tratar de espécies forrageiras, quando utilizadas para esses fins, cuidados especiais são necessários, como o isolamento da área, para evitar a entrada do elemento na cadeia trófica.

Accumulation, speciation, and coordination of arsenic in an inbred line and a wild type cultivar of the desert plant species Chilopsis linearis (Desert willow)

This study investigated the absorption of arsenic (As), sulfur (S), and phosphorus (P) in the desert plant Chilopsis linearis (Desert willow) . A comparison between an inbred line (red flowered) and wild type (white flowered) plants was performed to look for differential responses to As treatment. One month old seedlings were treated for 7 days with arsenate (As 2O 5, As V) at 0, 20, and 40 mg As V L −1. Results from the ICP-OES analysis showed that at 20 mg As V L −1, red flowered plants had 280 ± 11 and 98 ± 7 mg As kg −1 dry wt in roots and stems, respectively, while white flowered plants had 196 ± 30 and 103 ± 13 mg As kg −1 dry wt for roots and stems. At this treatment level, the concentration of As in leaves was below detection limits for both plants. In red flowered plants treated with 40 mg As V L −1, As was at 290 ± 77 and 151 ± 60 mg As kg −1 in roots and stems, respectively, and not detected in leaves, whereas white flowered plants had 406 ± 36, 213 ± 12, and 177 ± 40 mg As kg −1 in roots, stems, and leaves. The concentration of S increased in all As treated plants, while the concentration of P decreased in roots and stems of both types of plants and in leaves of red flowered plants. X-ray absorption spectroscopy analyses demonstrated partial reduction of arsenate to arsenite in the form of As-(SX) 3 species in both types of plants.

Arsenic contamination of Ronphibun residents associated with uses of arsenic-contaminated shallow-well water other than drinking

High levels of urinary arsenic have been reported among residents of an area of southern Thailand where many households have shallow wells heavily contaminated with arsenic. However, the finding that very few of the residents in this area have used contaminated shallow-well water for drinking or cooking in the last 10 years prompted this investigation. The aim was to identify the uses of shallow-well water by adult residents that were related to a positive association between shallow-well water and urinary arsenic levels. Information on shallow-well water use for all personal and domestic purposes was obtained and arsenic levels of household shallow-well water and urine (after refraining from seafood for 2 days) were measured. Urinary and shallow-well water arsenic levels were strongly positively associated among residents who regularly used shallow-well water for bathing (including washing face, hair, hands and feet) but not among residents regularly using arsenic-safe water for bathing or regularly using shallow-well water for other purposes, such as brushing teeth, domestic cleaning or washing food and utensils. The findings suggest that appreciable transdermal absorption of arsenic is possible and that successful abatement of human contamination with arsenic may require the provision of arsenic-safe water, not only for consumption but also for personal hygiene purposes.

Dermal Absorption of Arsenic from Soils as Measured in the Rhesus Monkey

Regulatory agencies have relied on dermal absorption data for soluble forms of arsenic as the technical basis for specific absorption values that are used to calculate exposure to arsenic in weathered soil. These evaluations indicate that percutaneous absorption of arsenic from soil ranges from 3.2 to 4.5% of the dermally applied dose, based on studies of arsenic freshly mixed with soil. When this value is incorporated into risk assessments and combined with other assumptions about dermal exposures to soil, the conclusion is often that dermal exposure to arsenic from soil may contribute significantly to overall exposure to arsenic in soil. Prior characterization research has indicated that the solubility of arsenic in soil varies, depending on the provenance of the soil, the source of the arsenic, and the chemical interaction of arsenic with other minerals present within the soil matrix. Weathering produces forms of arsenic that are more tightly bound within the soil and less available for absorption. Our research expands on prior in vivo studies to provide insights into the potential for dermal absorption of arsenic from the more environmentally relevant substrate of soil. Specifically, two soils with very high concentrations of arsenic were evaluated under two levels of skin hydration. One soil, containing 1400 mg/kg arsenic, was collected adjacent to a pesticide production facility in New York. The other soil, containing 1230 mg/kg arsenic, was collected from a residential area with a history of application of arsenical pesticides. Although the results of this research are constrained by the small study size dictated by the selection of an animal research model using monkeys, the statistical power was optimized by using a "crossover" study design, wherein each animal could serve as its own comparison control. No other models (animal or in vitro) were deemed adequate for studying the dermal absorption of soil arsenic. Our results show dermal absorption of soluble arsenic in solution to be 4.8 +/- 5.5%, which is similar to results reported earlier for arsenic in solution (and used by regulatory agencies in recommendations regarding dermal absorption of arsenic). Conversely, absorption following application of arsenic in the soil matrices resulted in mean estimated arsenic absorption of 0.5% or less for all soils, and all individual estimates were less than 1%. More specifically, following application of arsenic-bearing soils to the abdomens of monkeys, urinary arsenic excretion could not be readily distinguished from background. This was true across all five soil-dosing trials, including application of the two dry soils and three trials with wet soil. These findings are consistent with our understanding of the environmental chemistry of arsenic, wherein arsenic can be present in soils in complexed mineral forms. This research addresses an important component involved in estimating the true contribution of percutaneous exposures to arsenic in soil relative to exposures via ingestion. Our findings suggest that dermal absorption of arsenic from soil is truly negligible, and that EPA's current default assumption of 3% dermal absorption of arsenic from soils results in significant overestimates of exposure.

Subcellular Speciation Analysis of Trace Element Oxidation States Using Synchrotron Radiation Micro-X-ray Absorption Near-Edge Structure

Identification of chemical species at a subcellular level is a key to understand the mechanisms involved in the biology of chemical elements. When performed with a microbeam, X-ray absorption near-edge structure (micro-XANES) enables the direct speciation analysis of oxidation states in subcellular compartments avoiding cell fractionation and other preparation steps that might modify the chemical species. Here we report the principal characteristics in terms of spatial resolution, detection limit, reproducibility, and repeatability of a micro-XANES experimental setup based on Kirkpatrick-Baez X-ray focusing optics that maintains high flux of incoming radiation (>10(11) photons/s) at micrometric spatial resolution (1.5 x 4.0 microm2). Applications and limitations of this setup are illustrated by examples of iron and arsenic absorption spectra obtained from the cytosol, nucleus, and mitochondrial network of cultured cells. A better repeatability and sensitivity with no oxidation state modification and minimal beam damage is achieved when cells are analyzed in a frozen hydrated state, as compared to freeze-dried cells. This original experimental setup can now be applied for the direct speciation analysis of most trace elements at the subcellular level.

X-ray 영상기법을 이용한 비소 흡수가 고사리 내부 수액 거동에 미치는 영향 연구

The global environment is deteriorating at an alarming rate, despite of enhanced international environmental regulation. Many studies have been performed to reduce toxic pollutants. Recently, plant-based phytoremediation technology for moving toxic contaminants from soil and water has been receiving large attention. Arsenic-contaminated soil is one of the major pollutant sources for drinking water. Pteris erotica has been known as a hyper-accumulator of arsenic from soils. In this study, we investigated the effect of arsenic absorption on sap flow inside xylem vessels of Pteris. The synchrotron X-ray micro-imaging technique was employed to monitor the refilling process of water containing arsenic inside the xylem vessels of Pteris's leaves and stems non-invasively. The captured phase-contrast X-ray images show both anatomy of internal structure and transport of water inside Pteris. The exposure of Pteris to arsenic solution was found to increase largely the water raise speed in xylem vessels. The present results would provide important information needed for understanding the mechanisms of accumulation and transportation of toxic materials in plants.

Oral Bioavailability and Dermal Absorption of Arsenic From Soil: in Vivo Research and Progress Toward in Vitro Methods

P-604 Abstract: Between July 2002 and May 2005, the U.S. Strategic Environmental Research and Development Program sponsored research focused on understanding the bioavailability of metals in soils. The broad goals of this effort were to better understand what metals drive remedial decisions at metals-impacted sites, evaluate the relative bioavailability of these metals in soil to human and ecological receptors, and to assess the potential for developing simple bench-top (in vitro) methods that might be predictive of the results observed in animals (in vivo). This presentation will provide a brief overview of the full breadth of the research that was undertaken, and more detailed information regarding the study design and findings regarding the relative oral bioavailability, as measured in the cynomolgus monkey, and dermal absorption of arsenic from soils, as measured in the Rhesus monkey. Additionally, discussion of current progress toward developing in vitro methods for estimating the relative oral bioavailability arsenic from soil will be provided. This emerging research indicates that soil-related factors impose significant controls on the availability for arsenic to be absorbed under physiologic conditions, and that existing benchtop (in vitro) methods for assessing the bioaccessibility of other metals from soil may not be appropriate for evaluating the bioaccessibility of arsenic from soil.

Relative Oral Bioavailability of Arsenic from Contaminated Soils Measured in the Cynomolgus Monkey

A number of studies have found that gastrointestinal absorption of arsenic from soil is limited, indicating that a relative oral bioavailability (RBA) adjustment is warranted when calculating risks from exposure to arsenic-contaminated soil. However, few studies of arsenic bioavailability from soil have been conducted in animal models with phylogenetic similarity to humans, such as nonhuman primates. We report here the results of a study in which the RBA of arsenic in soil from a variety of types of contaminated sites was measured in male cynomolgus monkeys. A single oral dose of each contaminated soil was administered to five adult male cynomolgus monkeys by gavage, and the extent of oral absorption was evaluated through measurement of arsenic recovery in urine and feces. Urinary recovery of arsenic following doses of contaminated soil was compared with urinary recovery following oral administration of sodium arsenate in water in order to determine the RBA of each soil. RBA of arsenic in 14 soil samples from 12 different sites ranged from 0.05 to 0.31 (5-31%), with most RBA values in the 0.1-0.2 (10-20%) range. The RBA values were found to be inversely related to the amount of arsenic present with iron sulfate. No other significant correlations were observed between RBA and arsenic mineralogic phases in the test soils. The lack of clear relationships between arsenic mineralogy and RBA measured in vivo suggests that gastrointestinal absorption of arsenic from soil may be more complex than originally thought, and subject to factors other than simple dissolution behavior.

Optimisation of analytical parameters in inorganic arsenic (III and V) speciation by hydride generation using L-cysteine as prereducing agent in diluted HCl medium

The effects on the arsenic spectrophotometric absorption signal and hydride generation of the reaction medium (HCl: 0-0.05 M), reducing agent (NaBH4: 0.2-1% stabilised in NaOH: 0.2-1%), prereducing agent (L-cysteine: 0-2%) and contact time between L-cysteine and arsenic (III) and arsenic (V) solutions were investigated using FIA-HG-QFAAS. The speciation procedure involved three steps: (i) arsenic (III) determination immediately after the sample was mixed with L-cysteine; (ii) total arsenic determination after a 10 min-contact time between sample and L-cysteine by boiling in water bath at 90 ± 5°C and (iii) arsenic (V) determination as difference between total arsenic and arsenic (III). Under optimised conditions to generate arsine from arsenic (III) (0.01 M HCl, 0.2% L-cysteine, 0.6% NaBH4 in 0.5% NaOH), the arsenic speciation was possible with good recovery (98-105%) for arsenic (III), arsenic (V) and total arsenic. A rigorous pH control at 2.00 ±0.01 prior to arsine generation was necessary. The detection limit based on 3σ criteria and parameters of calibration curve was 0.1 ng mL-1 arsenic. The simple and inexpensive optimised method is used for the determination of leachable inorganic arsenic species within a distribution study of arsenic in the Baia-Mare area, Romania, which is the subject of another paper.

Percutaneous absorption of arsenic from environmental media

Current knowledge of percutaneous absorption of arsenic is based on studies of rhesus monkeys using soluble arsenic in aqueous solution, and soluble arsenic mixed with soil (Wester et al., 1993). These studies produced mean dermal absorption rates in the range of 2.0-6.4% of the applied dose. Subsequently, questions arose as to whether these results represent arsenic absorption from environmental media. Factors such as chemical interactions, the presence of other metals, and the effects of weathering on environmental media all can affect the nature of arsenic and its potential for percutaneous absorption. Therefore, research specific to more relevant matrices is important. The focus of this effort is to outline study design considerations, including particle size, application rates, means of ensuring skin contact and appropriate statistical evaluation of the data. Appropriate reference groups are also important. The potential for background exposure to arsenic in the diet possibly obscuring a signal from a dermally applied dose of arsenic will also be addressed. We conclude that there are likely to be many site- or sample-specific factors that will control the absorption of arsenic, and matrix-specific analyses may be required to understand the degree of percutaneous absorption.

Comparison of a Chemical and Enzymatic Extraction of Arsenic from Rice and an Assessment of the Arsenic Absorption from Contaminated Water by Cooked Rice

Rice is a target food for arsenic speciation based analyses because of its relatively high arsenic concentration and per capita consumption rates. Improved speciation data for rice can be helpful in estimating inorganic arsenic exposures in the U.S. and in endemic populations. The inorganic arsenic exposure for cooked rice should include both the arsenic in raw rice plus the arsenic absorbed from the water used to prepare it. The amount of arsenic absorbed from water by rice during preparation was assessed using five different types of rice cooked in both contaminated drinking water and arsenic-free reagent water. The rice samples were extracted using trifluoroacetic acid (TFA) and speciated using IC-ICP-MS. The TFA procedure was able to extract 84-104% of the arsenic (As) from the five different cooked rice samples. Chromatographic recoveries ranged from 99% to 116%. The dimethylarsinic acid (DMA) and inorganic arsenic concentration ranged from 22 to 270 ng of As/g of rice and from 31 to 108 ng of As/g of rice, respectively, for samples cooked in reagent water. The overall recoveries, which relate the sum of the chromatographic species back to the total digested concentration, ranged from 89% to 117%. The absorption of arsenic by rice from the total volume of water [1:1 to 4:1 (water:rice)] used in cooking was between 89% and 105% for two different contaminated drinking water samples. A comparison of the TFA extraction to an enzymatic extraction was made using the five rice samples and NIST 1568a rice flour. The two extraction procedures produced good agreement for inorganic arsenic, DMA, and the overall recovery. Through the use of IC-ESI-MS/ MS with a parent ion of m/z 153 and fragment ions of m/z 138, 123, and 105, the structure dimethylthioarsinic acid was tentatively identified in two of the rice samples using the enzymatic extraction.

Absorption of foliar-applied arsenic by the arsenic hyperaccumulating fern ( Pteris vittata L.)

The fact that heavy metals can enter various domains of the plant system through foliar pathways spurred us to explore if the fronds of the Chinese brake fern ( Pteris vittata L.), a hyperaccumulator of arsenic, a carcinogenic metalloid, was proficient in absorbing arsenic in the form of sprays. The specific objective of this study was to investigate the impact of frond age, form of arsenic, and time of application on the absorption of foliar-applied arsenic by the brake fern; also examined were the effects of foliar sprays on surface ultrastructure and arsenic speciation in the frond following absorption. Foliar sprays of different arsenic concentrations (0, 50, 100, 200, and 400 ppm) were applied to young and fertile fronds. A positive linear relationship existed between arsenic concentration and absorption; the arsenic concentration of fronds increased from 50 to 200 ppm. Time-course analysis with excised pinnae indicated an initial linear increase followed by a plateau at 48 h. The young fronds with immature sori absorbed more arsenic (3100 ppm) than the fertile mature fronds (890 ppm). In the frond, the arsenic absorption was greatest in the lamina of the pinnae followed by the sori and the rachis. Applying arsenic during night (20:00–22:00 h) or afternoon (12:00–14:00 h) resulted in greater absorption of arsenic than the application in the morning (08:00–10:00 h). The arsenic absorption was greater through abaxial surfaces than through adaxial surfaces. The brake fern absorbed more arsenic when it was applied in the form of arsenite. Regardless of the form of arsenic and the surface it was applied to, arsenic occurred as arsenite, the reduced and the most toxic form of arsenic, after having been absorbed by the fronds. Scanning electron microscopy revealed no surface morphological alterations following all arsenic sprays. The study unequivocally illustrated that the Chinese brake fern absorbed foliar-applied arsenic with great efficiency. Consequently, the arsenic concentrations in the fronds transcended the levels of hyperaccumulation; such a characteristic could be exploited in the phytoremediation of groundwater contaminated with arsenic.

Arsenic exposure alters activity behaviour of key nitrogen assimilatory enzymes in growing rice plants

Rice seedlings when grown in sand cultures for 5–20 days under 25 and 50 μM As2O3 in the medium showed a marked decline in growth when compared to controls. Increased absorption of arsenic from the medium, against the concentration gradient was observed. Greater localization of absorbed arsenic was noted in roots than in shoots. Rice plants grown for 20 days with 50 μmol l−1 arsenic in the medium accumulated upto 370 μmol arsenic kg−1 dry weight in roots. Increasing levels of As2O3in situ caused a marked decline in the activities of the nitrate assimilatory enzymes nitrate reductase (NR), nitrite reductase (NiR) and glutamine synthetase (GS), whereas an increase in the activities of alanine and aspartate aminotransferases was observed. The activities of aminating (NADH-GDH) and deaminating (NAD+-GDH) glutamate dehydrogenases increased at moderately toxic level (25 μM) of As2O3 whereas a higher As level of 50 μM was inhibitory to the enzymes. Addition of 1 M proline in the reaction medium caused significant restoration in As-led loss of NR and GS activities. NR and GS extracted from arsenic exposed seedlings showed higher Km values compared to the enzymes extracted from control-grown seedlings, whereas GDHs extracted from As-stressed seedlings showed a decrease in Km. Results suggest that inhibition in the activities of N assimilatory enzymes accompanied with decreased affinity of the enzymes towards their substrates would eventually lead to a marked suppression of N assimilation and impaired growth of rice seedlings in As polluted environment.

In vivo percutaneous absorption of arsenic from water and CCA-treated wood residue.

This study was conducted to evaluate the dermal absorption of arsenic from residues present on the surface of wood preserved with chromated copper arsenate (CCA). The research reported herein used methods parallel to those of earlier research on the dermal absorption of radiolabeled arsenic (R. C. Wester et al., 1993, Fund. Appl. Toxicol. 20, 336-340), with modifications to allow use of environmental matrices that are not radiolabeled. These modifications include the surface area of application and dietary intake of arsenic, thus maximizing the potential for detection of dermally absorbed arsenic in exposed animals above diet-associated background levels of exposure. Two forms of arsenic were administered in this work. The first, arsenic in solution, was applied to the skin of monkeys to calibrate the model against prior absorption research and to serve as the basis of comparison for absorption of arsenic from CCA-treated wood residues. The second substrate was residue that resides on the surface of CCA-treated wood. Results from this research indicate that this study methodology can be used to evaluate dermally absorbed arsenic without the use of a radiolabel. Urinary excretion of arsenic above background levels can be measured following application of soluble arsenic, and absorption rates (0.6-4.4% absorption) are consistent with prior research using the more sensitive, radiolabeled technique. Additionally, the results show that arsenic is poorly absorbed from CCA-treated wood residues (i.e., does not result in urinary arsenic excretion above background levels).

Children's exposure to arsenic from CCA-treated wooden decks and playground structures.

CCA-treated wood is widely used in the fabrication of outdoor decks and playground equipment. Because arsenic can be removed from the surface of CCA-treated wood both by physical contact and by leaching, it is important to determine whether children who play on such structures may ingest arsenic in quantities sufficient to be of public health concern. Based on a review of existing studies, it is estimated that arsenic doses in amounts of tens of micrograms per day may be incurred by children having realistic levels of exposure to CCA-treated decks and playground structures. The most important exposure pathway appears to be oral ingestion of arsenic that is first dislodged from the wood by direct hand contact, then transferred to the mouth by children's hand-to-mouth activity. The next most important pathway appears to be dermal absorption of arsenic, while ingestion of soil that has become contaminated by leaching from CCA-treated structures appears to be of lesser importance, except possibly in the case of children with pica. Considerable uncertainty, however, is associated with quantitative estimates of children's arsenic exposure from CCA-treated wood. Priorities for refining estimates of arsenic dose include detailed studies of the hand-to-mouth transfer of arsenic, studies of the dermal and gastrointestinal absorption of dislodgeable arsenic, and studies in which doses of arsenic to children playing in contact with CCA-treated wood are directly determined by measurement of arsenic in their urine, hair, and nails.

Effects of arsenic species and phosphorus on arsenic absorption, arsenate reduction and thiol formation in excised parts of Pteris vittata L.

Understanding the arsenic (As) detoxification mechanisms employed by the newly discovered As hyperaccumulator Chinese Brake fern ( Pteris vittata L.) is important to optimize As accumulation capability. The present experiment was carried out to determine the location of As reduction and thiol formation in Chinese Brake fern and the ability of excised plants to absorb As under P influence. Live Chinese Brake ferns were separated into three parts: pinnae (leaflets), fronds (aboveground biomass, de-rooted), and roots (belowground biomass, de-topped). The excised plants were then exposed to 0.5-strength Hoagland nutrient solutions containing 667 μM As(III), As(V), or monomethylarsonic acid (MMA) and 0 μM P or 500 μM P for 1 day. Arsenate and arsenite were separated using an As speciation cartridge and As was determined by graphite furnace atomic absorption spectrophotometry (GFAAS). The pinnae absorbed the greatest amounts of As followed by fronds and roots. In the presence of P, the phytoavailability of As species was As(III)>MMA>As(V) for pinnae and roots and As(V)>As(III)≅MMA for fronds. The fact that As(III) was the predominant form in excised aerial tissues whereas As(V) was the main form in excised roots clearly demonstrated that As reduction occurred mostly in the fronds, mainly in the pinnae. Absorption of As species resulted in formation of thiol, with MMA causing the greatest level of formation. Although addition of P to the solution suppressed As(V) accumulation in excised pinnae and roots, it enhanced As(V) reduction, and reduced thiol production. The results suggested that the ability to efficiently reduce As(V), facilitated by P, and to quickly produce thiols might have both contributed to the capability of Chinese Brake fern to hyperaccumulate As.

Portable X-ray fluorescence in the characterisation of arsenic contamination associated with industrial buildings at a heritage arsenic works site near Redruth, Cornwall, UK.

An investigation using in situ analysis by portable X-ray fluorescence (PXRF) has shown that contamination present on industrial buildings at a heritage arsenic works site near Redruth, Cornwall, UK results from the absorption of arsenic by porous and semi-porous building materials that were in contact with arsenic-rich flue gases. Results from a preliminary survey indicate that arsenic remains locked in these materials and is being gradually leached out by weathering processes. This weathering causes general contamination of the adjacent building surfaces averaging 1845 microg g(-1) arsenic, presumably caused by evaporation of leach solutions in contact with air at the surface of the building materials. More extensive crystalline deposits were found under arches protected from dissolution and further dispersion by rain water. These deposits appeared to comprise calcium sulfate (gypsum), associated with on average between 1.2 and 6.8% m/m As. In situ PXRF proved to be highly effective in locating sources of contamination at the site and in providing data that allowed a hypotheses for the origin of this contamination to be formulated and tested in the field.