Methylarsonic Acid Research Articles

Simultaneous speciation of arsenic and selenium in human urine by high-performance liquid chromatography inductively coupled plasma mass spectrometry

A procedure for the simultaneous determination of six selenium species and six arsenic species in human urine by ion-pair, reversed-phase liquid chromatography coupled to ICP-MS has been developed. Selenium species, trimethylselenonium ion (TMSe), selenocystine (SeCys), selenite (SeIV), selenourea (SeUr), selenomethionine (SeMet), selenoethionine (SeEt), and arsenic species, arsenocholine (AsC), arsenobetaine (AsB), dimethylarsinic acid (DMA), methylarsonic acid (MMA), arsenite (AsIII), arsenate (AsV) were separated on a C8 reversed phase column by a mobile phase of 13.0 mmol l−1 tetrabutylammonium hydroxide (ion-pair reagent) and 1.3% methanol at pH 5.7–5.8 (adjusted with malonic acid). The total analysis took less than 10 min with isocratic elution at a flow rate of 1.0 ml min−1, and was free from chloride interference due to the complete separation of the analyte species from chloride. The detection limits, in synthetic urine for an injection volume of 50 μL, ranged between 0.1 and 0.4 μg l−1 for the six arsenic species (except AsC) and between 0.7 and 2 μg l−1 for the six selenium species (at m/z 78). The repeatability was less than 10% (RSD) for 1 μg l−1 arsenic species and 5 μg l−1 selenium species, except for AsC. Quantification was based on response factors in a synthetic urine matrix relative that of AsV in the mobile phase. The response factors for selenium species showed considerable compound dependence. Recoveries from spiked urine samples ranged from 81% to 103%, except for SeUr and SeEt, which were not recovered. The method was applied to the determination of arsenic and selenium species in urine, which only required filtering through a 0.45 μm membrane filter and dilution with mobile phase in order to measure arsenic and selenium urinary metabolites.

Molecular Mechanisms of the Diabetogenic Effects of Arsenic: Inhibition of Insulin Signaling by Arsenite and Methylarsonous Acid

Molecular Mechanisms of the Diabetogenic Effects of Arsenic: Inhibition of Insulin Signaling by Arsenite and Methylarsonous Acid

Mammalian glucose permease GLUT1 facilitates transport of arsenic trioxide and methylarsonous acid

Arsenic exposure is associated with hypertension, diabetes, and cancer. Some mammals methylate arsenic. Saccharomyces cerevisiae hexose permeases catalyze As(OH) 3 uptake. Here, we report that mammalian glucose transporter GLUT1 catalyzes As(OH) 3 and CH 3As(OH) 2 uptake in yeast or in Xenopus laevis oocytes. Expression of GLUT1 in a yeast lacking other glucose transporters allows for growth on glucose. Yeast expressing yeast HXT1 or rat GLUT1 transport As(OH) 3 and CH 3As(OH) 2. The K m of GLUT1 is to 1.2 mM for CH 3As(OH) 2, compared to a K m of 3 mM for glucose. Inhibition between glucose and CH 3As(OH) 2 is noncompetitive, suggesting differences between the translocation pathways of hexoses and arsenicals. Both human and rat GLUT1 catalyze uptake of both As(OH) 3 and CH 3As(OH) 2 in oocytes. Thus GLUT1 may be a major pathway uptake of both inorganic and methylated arsenicals in erythrocytes or the epithelial cells of the blood–brain barrier, contributing to arsenic-related cardiovascular problems and neurotoxicity.

Response of Pepper Plants (Capsicum annum L.) on Soil Amendment by Inorganic and Organic Compounds of Arsenic

The influence of soil contamination by inorganic and organic arsenic compounds on uptake, accumulation, and transformation of arsenic in pepper (Capsicum annum L.) was investigated in greenhouse pot experiments under controlled conditions. Pepper plants were cultivated in substrate amended by aqueous solutions of arsenite, arsenate, methylarsonic acid (MA), and dimethylarsinic acid (DMA) applied individually into cultivation substrate at concentrations of 15 mg As per kg of substrate. The plant availability of the arsenicals increased in the order arsenite = arsenate < MA < DMA. The highest arsenic concentrations were found in roots followed by stems, leaves, and fruits regardless of arsenic compound applied. In the control samples of pepper fruits, As(III), As(V), and DMA were present (25%, 37%, and 39% of the water-extractable arsenic). In control stems + leaves and roots, As(V) was the major compound (63% and 53% in a phosphate buffer extract) followed by As(III) representing 33% and 42%. Additionally, low concentrations (not exceeding 5%) of DMA and MA were detected as well. In all the soils analyzed after the first harvest of pepper fruits, arsenate was the dominating compound followed by arsenite. Methylarsonic acid, methylarsonous acid, and DMA were present at varying concentrations depending on the individual soil treatments. In the treated plants, the arsenic compounds in plant tissues reflected predominantly the extractable portions of arsenic compounds present in soil after amendment, and this pattern was more significant in the first part of vegetation period. The results confirmed the ability of generative parts of plants to accumulate preferably organic arsenic compounds, whereas in the roots and aboveground biomass, mainly inorganic arsenic species are present. Evidently, the source of soil arsenic contamination affects significantly the extractable portions of arsenic compounds in soil and subsequently the distribution of arsenic compounds within the plants.

Seaweeds Along KwaZulu-Natal Coast of South Africa—4: Elemental Uptake by Edible Seaweed Caulerpa racemosa (Sea grapes) and the Arsenic Speciation

The elemental uptake by edible seaweed Caulerpa racemosa (Sea grapes), a marine macroalgae (chlorophyta, green alga) grown richly along KwaZulu-Natal coastline. The total concentrations of seven elements, namely Mn, Fe, As, B, Ti, Zn and Hg in Caulerpa racemosa were monitored for a one-year cycle (June 2002 to May 2003) at four selected sampling sites spread over 150 km wide from North to South. The C. racemosa possess high arsenic, boron and titanium accumulating ability, but low iron uptake. A typical C. racemosa sample at Treasure Beach in the vicinity of Durban Metropolis in autumn contained Mn (5.2 ± ppm), Fe (0.21 ± 0.01 ppm), As (8.5 ± 0. ppm), B (1090 ± ppb), Ti (159 ± ppb), Zn (3.8 ± 0.1 ppb), and Hg (189 ± ppb). The general trend found at all sites was high elemental concentrations in winter and a decrease in concentrations from winter to spring and summer. C. racemosa recorded highest mercury levels (>205 ppb) during the summer season at the Zinkwasi site. The arsenic speciation in four abundant seaweeds from the beaches of Indian Ocean in the KwaZulu-Natal coast is investigated. The speciation of arsenic in two rhodophyta seaweeds, Plocamium corallorhiza and Gelidium abbottiorum, and two chlorophyta seaweeds, Ulva lactuca and Caulerpa racemosa at four sampling sites during the summer of 2003, is elucidated. Caulerpa racemosa had highest total arsenic (in ppb) reaching (8850 ± 200) at Zinkwasi, and the concentrations of the other arsenic species analysed are As (III) (194 ± 10), As(V) (568 ± 27), methylarsonic acid (494 ± 22) and dimethylarsinic acid (373 ± 12). In an indirect estimation, C. racemosa had 81 ± 2% aresenosugars.

Quantitation of Toxic Arsenic Species and Arsenobetaine in Pacific Oysters Using an Off-line Process with Hydride Generation−Atomic Absorption Spectroscopy

An off-line process-based speciation technique was devised here to quantitatively determine toxic inorganic arsenic (iAs), methylarsonic acid (MA), dimethylarsinic acid (DMA), and the dominant, albeit virtually nontoxic, arsenobetaine (AB) in Pacific oysters (Crassostrea gigas). Oysters were extracted with fresh methanol-water (8+2), and this was replicated three times. They were then evaporated to near dryness and subsequently redissolved in pure water; defatting was then performed with a C18 cartridge. The trace hydride active arsenic species, that is, iAs, MA, and DMA, in the defatted solutions were determined with a sensitive hydride generation-packed coldfinger trap-atomic absorption spectrometric (HG-PCFT-AAS) coupled system. The arsenicals that were desorbed from the cation-exchange resin (Dowex 50W-X8) in the washings of 4 M NH3 were categorized on the basis of AB + DMA. The total quantity of arsenic in the recovered AB + DMA was determined with a commercial hydride generation-atomic absorption spectrometric (HG-AAS) system, and finally, AB was calculated from (AB + DMA) - DMA. The average concentrations of iAs, MA, DMA, AB, and total arsenic (TAs) in the oysters collected from six aquacultural sites along the west coast of Taiwan were, respectively, 0.15, 0.06, 0.64, 6.93, and 13.74 mg kg(-1) of dry weight. AB was the major species, whereas iAs (arsenite + arsenate) were the most toxic species, although the iAs made up only approximately 1% of the TAs in the oysters. The lifetime target cancer risk, as determined by the concentration of iAs on a fresh weight basis in the oysters, was well below the ordinary health protection criteria (10(-6)).

The response of tomato (Lycopersicon esculentum) to different concentrations of inorganic and organic compounds of arsenic

AbstractTomato plants were cultivated in greenhouse and water solutions of arsenite (As(III)), arsenate (As(V)), methylarsonic acid (MA) and dimethylarsinic acid (DMA) were applied individually into cultivation substrate at two As levels, 5 and 15 mg kg−1 of the substrate. Comparing the availability of arsenic compounds increased in order arsenite = arsenate &lt; MA &lt; DMA where the arsenic contents in plants decreased during vegetation period. Within a single plant, the highest arsenic concentration was found in roots followed in decreasing order by leaves, stems, and fruits regardless of arsenic compound applied. Arsenic toxicity symptoms reflected in suppressed growth of plants and a lower number and size of fruits were most significant with DMA treatment. However, the highest accumulation of arsenic by plants growing in the soil containing DMA was caused by higher mobility of this compound in the soil due to its lower sorption affinity. Our results confirmed substantial role of transformation processes of arsenic compounds in soil in uptake and accumulation of arsenic by plants.

Iron antagonism of MSMA herbicide applied to bermudagrass: characterization of the Fe2+-MAA complexation reaction

Discoloration of bermudagrass often results from application of MSMA herbicide used to control southern crabgrass and other weeds. However, when products containing iron sulfate (FeSO4) are tank-mixed with MSMA, this discoloration is reduced. Experiments investigated the effect of tank-mixing organic arsenical herbicides with FeSO4or a chelated iron source (Sprint 330) in terms of southern crabgrass control and injury to bermudagrass. Tank-mixing MSMA with FeSO4reduced bermudagrass injury. However, southern crabgrass control was also reduced by at least 50% with the addition of ≥0.38 kg Fe2+ha−1. Neither antagonism nor safening of bermudagrass was observed when the chelated Fe2+source was used. Applying FeSO4as a separate treatment 1 to 4 d before or after MSMA application did not reduce visual burmudagrass injury 1 wk after treatment. Solution pH and FeSO4concentration controlled the extent of complexation and level of antagonism observed in the field; inorganic Fe2+reacted with MSMA to form a complex having reduced herbicidal activity. Potentiometric and spectrophotometric investigations found that methylarsonate, the parent acid of MSMA and other organic arsenical herbicides, reacts with inorganic Fe2+to form a stable 1:1 Fe2+-methylarsonic acid chelate having two points of metal coordination and a stability constant log10(β) = 2.77 ± 0.04. Tank-mixing MSMA with FeSO4to protect against bermudagrass injury negates the benefit of applying the herbicide for weed control, and therefore is not a recommendable practice for turf managers.

Dithiol Compounds at Low Concentrations Increase Arsenite Toxicity

Inorganic trivalent arsenicals are vicinal thiol-reacting agents, and dithiothreitol (DTT) is a well-known dithiol agent. Interestingly, both decreasing and increasing effects of DTT on arsenic trioxide-induced apoptosis have been reported. We now provide data to show that, at high concentrations, DTT, dimercaptosuccinic acid (DMSA), and dimercaptopropanesulfonic acid (DMPS) decreased arsenic trioxide-induced apoptosis in NB4 cells, a human promyelocytic leukemia cell line. In contrast, at low concentrations DTT, DMSA, and DMPS increased the arsenic trioxide-induced apoptosis. DTT at a high concentration (3 mM) decreased, whereas at a low concentration (0.1 mM), it increased the cell growth inhibition of arsenic trioxide, methylarsonous acid (MMA(III)), and dimethylarsinous acid (DMA(III)) in NB4 cells. DMSA and DMPS are currently used as antidotes for acute arsenic poisoning. These two dithiol compounds also show an inverse-hormetic effect on arsenic toxicity in terms of DNA damage, micronucleus induction, apoptosis, and colony formation in experiments using human epithelial cell lines derived from arsenic target tissues such as the kidney and bladder. With the oral administration of dithiols, the concentrations of these dithiol compounds in the human body are likely to be low. Therefore, the present results suggest the necessity of reevaluating the therapeutic effect of these dithiol compounds for arsenic poisoning.

Clinical Pharmacokinetic Study of Arsenic Trioxide in an Acute Promyelocytic Leukemia (APL) Patient: Speciation of Arsenic Metabolites in Serum and Urine

The pharmacokinetics of arsenic species in a Japanese patient with relapsed acute promyelocytic leukemia (APL) treated with arsenic trioxide at a daily dose of 0.08 mg/kg was investigated. After achieving complete remission on Day 35 during the induction therapy of arsenic trioxide, we collected the serum and urine samples on Days 4 and 5 during the consolidation therapy of arsenic trioxide. The concentrations of inorganic arsenic and the methylated metabolites in serum and urine were measured by HPLC/ICP-MS. The patient restricted taking the seafood for 3 d before the start of administration and during the sampling period in order to avoid the influence of arsenic derived from seafood. Arsenite (As(III)), methylarsonic acid (MMAs(V)), and dimethylarsinic acid (DMAs(V)) were detected in serum and urine. The total concentration of As(III), MMAs(V) and DMAs(V) in serum ranged from 18 to 41 microg/l (240-547 nM) during 24 h on Day 4. The amount of total arsenic (As(III)+MMAs(V)+DMAs(V)) in urine was 4464 microg/d on Day 4. These results suggest that not the micro-molar but the nano-molar order of arsenic in serum is sufficient to produce the therapeutic effect on APL cells.

Methylarsonous Acid Transport by Aquaglyceroporins

Many mammals methylate trivalent inorganic arsenic in liver to species that are released into the bloodstream and excreted in urine and feces. This study addresses how methylated arsenicals pass through cell membranes. We have previously shown that aquaglyceroporin channels, including Escherichia coli GlpF, Saccharomyces cerevisiae Fps1p, AQP7, and AQP9 from rat and human, conduct trivalent inorganic arsenic [As(III)] as arsenic trioxide, the protonated form of arsenite. One of the initial products of As(III) methylation is methylarsonous acid [MAs(III)], which is considerably more toxic than inorganic As(III). In this study, we investigated the ability of GlpF, Fps1p, and AQP9 to facilitate movement of MAs(III) and found that rat aquaglyceroporin conducted MAs(III) at a higher rate than the yeast homologue. In addition, rat AQP9 facilitates MAs(III) at a higher rate than As(III). These results demonstrate that aquaglyceroporins differ both in selectivity for and in transport rates of trivalent arsenicals. In this study, the requirement of AQP9 residues Phe-64 and Arg-219 for MAs(III) movement was examined. A hydrophobic residue at position 64 is not required for MAs(III) transport, whereas an arginine at residue 219 may be required. This is similar to that found for As(III), suggesting that As(III) and MAs(III) use the same translocation pathway in AQP9. Identification of MAs(III) as an AQP9 substrate is an important step in understanding physiologic responses to arsenic in mammals, including humans.

Comparison of mild extraction procedures for determination of plant-available arsenic compounds in soil

In this work three mild extraction agents for determination of plant-available fractions of elements in soil were evaluated for arsenic speciation in soil samples. Pepper (Capsicum annum, L.) var. California Wonder was cultivated in pots, and aqueous solutions of arsenite, arsenate, methylarsonic acid, and dimethylarsinic acid, at a concentration of 15 mg As kg(-1) soil, were added at the beginning of the experiment. Control pots (untreated) were also included. Deionized water, 0.01 mol L(-1) CaCl2, and 0.05 mol L(-1) (NH4)2SO4 were used to extract the plant-available fraction of the arsenic compounds in soil samples collected during the vegetation period of the plants. Whereas in control samples the extractable arsenic fraction did not exceed 1% of total arsenic content, soil amendment by arsenic compounds resulted in extraction of larger amounts, which varied between 1.4 and 8.1% of total arsenic content, depending on soil treatment and on the extracting agent applied. Among arsenic compounds determined by HPLC-ICPMS arsenate was predominant, followed by small amounts of arsenite, methylarsonic acid, and dimethylarsinic acid, depending on the individual soil treatment. In all the experiments in which methylarsonic acid was added to the soil methylarsonous acid was detected in the extracts, suggesting that the soil bacteria are capable of reducing methylarsonic acid before a further methylation occurs. No significant differences were observed between analytical data obtained by using different extraction procedures.

Methyl Arsenic Adsorption and Desorption Behavior on Iron Oxides

In virtually all Earth surface environments, methylated forms of arsenic can be found. Because of the widespread distribution and toxicity of methyl-arsenic compounds, their adsorption by soil minerals is of considerable interest. The objective of this study was to compare the adsorption and desorption behavior of methylarsonic acid (MMAsV), methylarsonous acid (MMAsIII), dimethylarsinic acid (DMAsV), dimethylarsinous acid (DMAsIII), arsenate (iAsV), and arsenite (iAsIII) on iron oxide minerals (goethite and 2-line ferrihydrite) by means of adsorption isotherms, adsorption envelopes, and desorption envelopes (using sulfate and phosphate as desorbing ligands). MMAsIII and DMAsIII were not appreciably retained by goethite or ferrihydrite within the pH range of 3 to 11, while iAsIII was strongly adsorbed to both iron oxides. MMAsV and iAsV were adsorbed in higher amounts than DMAsV on goethite and ferrihydrite at all pH values studied. MMAsV and iAsV exhibited high adsorption affinities on both goethite and ferrihydrite from pH 3 to 10, while DMAsV was adsorbed only at pH values below 8 by ferrihydrite and below 7 by goethite. All arsenic compounds were desorbed more efficiently by phosphate than sulfate. MMAsV, iAsV, and DMAsV each exhibited adsorption characteristics suggesting specific adsorption on both goethite and ferrihydrite. Increased methyl substitution resulted in both decreased adsorbed arsenic at low arsenic concentrations in solution and increased ease of arsenic release from the iron oxide surface.

Comparison of mild extraction procedures for determination of arsenic compounds in different parts of pepper plants (Capsicum annum, L.)

AbstractEight extraction agents (water, methanol–water mixtures in various ratios, methanol, a 20 mmol l−1 ammonium phosphate buffer, and a methanol–phosphate buffer) were tested for the extraction of arsenic compounds from fruits, stems + leaves, and roots of pepper plants grown on soil containing 17.2 mg kg−1 of total arsenic. The arsenic compounds in the extracts were determined using high‐performance liquid chromatography–hydride generation inductively coupled plasma mass spectrometry. Whereas pure water was the most effective extraction agent for fruits (87 ± 3.3% extraction yield) and roots (96 ± 0.6% extraction yield), the 20 mM ammonium phosphate buffer at pH 6 extracted about 50% of the arsenic from stems + leaves. Decreasing extractability of the arsenic compounds was observed with increasing methanol concentrations for all parts of the pepper plant. In pepper fruits, arsenic(III), arsenic(V), and dimethylarsinic acid (DMA) were present (25%, 37%, and 39% respectively of the extractable arsenic). Arsenic(V) was the major compound in stems + leaves and roots (63% and 53% respectively), followed by arsenic(III) representing 33% and 42% respectively, and small amounts (not exceeding 5%) of DMA and methylarsonic acid were also detected. Hence, for a quantitative extraction of arsenic compounds from different plant tissues the extractant has to be optimized individually. Copyright © 2005 John Wiley &amp; Sons, Ltd.

A rapid and novel alternative to conventional sample treatment for arsenic speciation in rice using enzymatic ultrasonic probe

This work proposes an arsenic speciation method, which reduces the sample treatment time from several hours, required by other extraction procedures, to only a few minutes. No organic solvents have to be used and several extraction steps can be avoided, thus diminishing possible sources of error. Total As was determined by ICP–MS and major arsenic species present in rice (As (III), As (V), methylarsonic acid (MMA) and dimethyarsinic acid (DMA)) were quantified by LC–ICP–MS. Different treatments for extraction were evaluated: aqueous, methanol and tetramethyl ammonium hydroxide (TMAH) extraction as well as enzymatic hydrolysis. Several parameters were optimised, such as sonication time, amplitude, immersion depth of the probe into the solution, extraction temperature, etc. Quantitative extraction for total arsenic (>95%) and 90% extraction for the sum of the arsenic species without species transformation were obtained by applying an enzymatic treatment using an aqueous mixture of protease XIV and α-amylase in only 3 min. A disruption of the cell membranes due to the focused sonication energy, which alleviates enzyme attack, seems to be the responsible of such extraction enhancement. The method was applied to a rice sample used in an inter-comparison exercise (SEAS G6RD-CT2001-00473) and to two commercial rice samples. The method was validated for total arsenic extraction by analysing a certified reference material from NIST (SRM 1568a).

Placental transfer of arsenic to fetus of Dall’s porpoises ( Phocoenoides dalli)

Concentrations of total arsenic and individual arsenic compounds were determined in liver, muscle, kidney and blubber of mother and fetus of Dall’s porpoises collected from off Sanriku, Japan, in the year 2000 to characterize the placental transfer of arsenic to fetus in cetaceans. Arsenic was detected in all the tissues of Dall’s porpoises. Total arsenic concentrations in liver, kidney, muscle and blubber were 0.76, 0.69, 0.35 and 0.55 μg/g wet wt, respectively, for mother and 0.28, 0.23, 0.26 and 0.07 μg/g wet wt, respectively, for fetus. In all the tissues, concentrations of total arsenic in mother Dall’s porpoise were higher than in fetus. Arsenic speciation revealed that arsenobetaine was the major arsenic compound in liver, kidney and muscle of both mother and fetus. The percentage of arsenobetaine to total arsenic ranged from 76.0 to 91.0% in the tissues. Dimethylarsinic acid, arsenocholine, methylarsonic acid and an unidentified arsenic compound were also detected in tissues of both mother and fetus as minor constituents, whereas tetramethylarsonium ion was not detected in tissues of the fetus. These results suggest that arsenobetaine, dimethylarsinic acid, arsenocholine and methylarsonic acid are transferable from mother to fetus in Dall’s porpoises. To our knowledge, this is the first report on placental transfer of arsenic compounds to fetus in marine mammals.

Distribution and fate of biologically formed organoarsenicals in coastal marine sediment

Marine organisms, including phyto- and zoo-plankton, macroalgae, and animals, concentrate arsenic in various organic forms. However, the distribution and fate of these organoarsenicals in marine environments remains unclear. In this study, the distribution of organoarsenicals in coastal marine sediment in Otsuchi Bay, Japan, has been determined. Methylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, arsenobetaine, arsenocholine and other unidentified arsenic species were detected in marine sediment by high-performance liquid chromatography–inductively coupled plasma mass spectrometry analysis of methanol–water extracts. Arsenobetaine was the dominant organoarsenical at four of the seven stations where tests were carried out, and unidentified species or dimethylarsinic acid dominated at the other stations. Total organoarsenicals (as arsenic) in the surface sediment amounted to 10.6–47.5 µg kg−1 dry sediment. Core analysis revealed that concentrations of organoarsenicals decreased with depth, and they are considered to be degraded within 60 years of deposition. These results show that organoarsenicals formed by marine organisms are delivered to the sediment and can be degraded within several decades. Copyright © 2005 John Wiley & Sons, Ltd.

Decomposition of organoarsenic compounds for total arsenic determination in marine organisms by the hydride generation technique

The conditions necessary for the complete decomposition of six organic arsenic compounds, namely methylarsonic acid (MMAA), dimethylarsinic acid (DMAA), trimethylarsine oxide, tetramethylarsonium iodide, arsenocholine bromide (AsC) and arsenobetaine (AB), were investigated. The degree of decomposition of the arsenic compounds was monitored using a hydride generation (HYD) technique, because the response from this system depends strongly on the chemical species of arsenic, with inorganic arsenic (the expected product from these decomposition experiments) giving a much more intense HYD signal than the organic arsenic compounds. The arsenic compounds were decomposed by heating them with three types of acid mixture, namely HNO3HClO4, HNO3HClO4HF, or HNO3HClO4H2SO4. Both MMAA and DMAA were decomposed completely using any of the mixed acids at a decomposition temperature of 200 °C or higher. The HNO3HClO4H2SO4 mixture was the most effective for decomposing AsC and AB, which are the most difficult compounds among all types of organic arsenic compound to decompose and render inorganic. The complete decomposition of AB was only achieved, however, when the temperature was 320 °C or higher, and the sample was evaporated to dryness. When the residue from this treatment was examined by high-performance liquid chromatography combined with inductively coupled plasma atomic emission spectrometry, all of the arsenic was found to be present as arsenic(V). The optimized conditions (HNO3HClO4H2SO4 at 320 °C) for decomposing AB were then used to determine the total amount of arsenic in marine organisms known to contain AB. Copyright © 2005 John Wiley & Sons, Ltd.

Methylarsonous Acid Transport by Aquaglyceroporins

Methylarsonous Acid Transport by Aquaglyceroporins

Influence of Pyrithiobac Application Rate and Timing on Weed Control and Cotton Yield in Greece1

Field experiments were conducted at four locations (Larissa, Halkidona, Thessaloniki, and Halastra) in Greece to evaluate weed and cotton response to various pyrithiobac rates applied preplant incorporated (PPI), preemergence (PRE), or postemergence (POST). Pyrithiobac applied PPI or PRE at 0.068, 0.102, or 0.136 kg ai/ha controlled black nightshade, pigweeds, and common purslane at Larissa. However, pyrithiobac applied PRE at Thessaloniki and Halkidona was more effective against black nightshade and pigweeds than pyrithiobac applied PPI. Pyrithiobac applied PPI or PRE at 0.068 or 0.102 kg/ha did not control common lambsquarters at Thessaloniki. Weed control with trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE at Larissa was slightly lower than that obtained with pyrithiobac. At Halkidona, trifluralin plus fluometuron applied PPI and alachlor plus fluometuron applied PRE provided weed control similar to that obtained with pyrithiobac. But at Thessaloniki, these treatments provided better weed control than pyrithiobac. Furthermore, pyrithiobac applied early postemergence (EPOST), midpostemergence, or in sequential systems controlled black nightshade and pigweeds, but it resulted in fair to good control of common purslane, velvetleaf, and common cocklebur. None of the POST treatments controlled common lambsquarters. Fluometuron EPOST controlled black nightshade, common lambsquarters, and common purslane ≥70, 86, and 67%, respectively. Fluometuron EPOST did not control pigweeds, velvetleaf, and common cocklebur. Cotton treated with pyrithiobac, regardless of method of application, yielded similar to the weed-free control. Cotton treated with pyrithiobac PPI at the highest rate (0.136 kg/ ha) yielded less at Halkidona, although adverse effects after its application were not visually apparent. Yield of cotton treated with herbicides was similar, with no difference among treatments.Nomenclature: Alachlor; fluometuron; pyrithiobac; trifluralin; black nightshade, Solanum nigrum L. #3 SOLNI; common cocklebur, Xanthium strumarium L. # XANST; common lambsquarters, Chenopodium album L. # CHEAL; common purslane, Portulaca oleracea L. # POROL; prostrate pigweed, Amaranthus blitoides S. Wats AMABL; redroot pigweed, Amaranthus retroflexus L. # AMARE; velvetleaf, Abutilon theophrasti Medicus # ABUTH; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘Hazera Vered’, ‘Deltapine 20’, ‘Deltapine 50’, ‘Stoneville Bravo’.Additional index words: Application timing, cotton herbicide, crop injury, residual activity.Abbreviations: EPOST, early postemergence; MPOST, midpostemergence; MSMA, monosodium salt of methylarsonic acid; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting; WAT, weeks after treatment.