Analysis of arsenic induced physiological and biochemical responses in a medicinal plant,Withania somnifera

Withania somnifera has been an important herb in the Ayurvedic and indigenous medical systems for centuries in India. However, these grow as weeds mostly in the wastelands, which receive contaminated water from municipal and industrial sources. In the present investigation, plants of Withania somnifera were exposed to various concentrations of arsenate (AsV) and arsenite (AsIII) (0, 10, 25, 50, 100 μM) for 10 days and analysed for accumulation of arsenic (As) and physiological and biochemical changes. Plants showed more As accumulation upon exposure to AsIII (320 μg g⁻¹ DW in roots and 161 μg g⁻¹ DW in leaves) than to AsV (173 μg g⁻¹ DW in roots and 100 μg g⁻¹ DW in leaves) after 10 days of treatment. Consequently, AsIII exposure caused more toxicity to plants as compared to that AsV, as evaluated in terms of the level of photosynthetic pigments and oxidative stress parameters (superoxide, hydrogen peroxide and lipid peroxidation), particularly at higher concentrations and on longer durations. Plants could tolerate low concentrations (variable for AsIII and AsV) until longer durations (10 days) and high concentrations for shorter durations (1–5 days) through increase in antioxidant enzymes and by augmented synthesis of thiols. In conclusion, As tolerance potential of Withania plants on one hand advocates its prospective use for remediation under proper supervision and on the other demonstrates possible threat of As entry into humans due to medicinal uses.     

Species variations in the biliary and urinary excretion of arsenate, arsenite and their metabolites

In most mammalian species, inorganic arsenicals are extensively biotransformed and excreted both in unchanged form and as metabolites. In the bile of rats receiving arsenate (AsV) or arsenite (AsIII) we have identified monomethylarsonous acid (MMAsIII), purportedly the most toxic metabolite of inorganic arsenic. As rats are not commonly accepted for studying arsenic metabolism, we carried out a comparative investigation on the excretion of AsV, AsIII and their metabolites in five animal species in order to determine whether they also form MMAsIII from AsV and AsIII. Anaesthetised bile duct-cannulated rats, mice, hamsters, rabbits, and guinea pigs were injected with AsV or AsIII (50 micromol/kg, i.v.) and their bile and urine was collected for 2 h. Arsenic in bile and urine was speciated by HPLC-hydride generation-atomic fluorescence spectrometry and the excretion rates of AsV, AsIII, monomethylarsonic acid (MMAsV), MMAsIII and dimethylarsinic acid (DMAsV) were quantified. All species injected with AsV excreted arsenic preferentially into urine, whereas all animals receiving AsIII, except rabbits, delivered more arsenic into bile than urine. Bile contained almost exclusively trivalent arsenic (i.e. AsIII and/or MMAsIII), whereas AsV, AsIII and DMAsV appeared in urine. Except for guinea pigs, which do not methylate arsenic, the other species formed MMAsIII and excreted it into bile. Having excreted as much as 8% of the dose of AsIII or AsV in 2 h as MMAsIII, rats were by far the most efficient producers of this supertoxic metabolite. Thus, although the rat is not a good model for studying long-term arsenic disposition, this species appears especially valuable in studies on AsIII methyltransferase and in vivo formation of MMAsIII.     

Effects of arsenic species and concentrations on arsenic accumulation by different fern species in a hydroponic system

Two hydroponic experiments were conducted to evaluate factors affecting plant arsenic (As) hyperaccumulation. In the first experiment; two As hyperaccumulators (Pteris vittata and P. cretica mayii) were exposed to 1 and 10 mg L(-1) arsenite (AsIII) and monomethyl arsenic acid (MMA) for 4 wk. Total As concentrations in plants (fronds and roots) and solution were determined In the second experiment P. vittata and Nephrolepis exaltata (a non-As hyperaccumulator) were exposed to 5 mgL(-1) arsenate (AsV) and 20 mgL(-1) AsIIIfor 1 and 15 d. Total As and AsIII concentrations in plants were determined Compared to P. cretica mayii, P. vittata was more efficient in arsenic accumulation (1075-1666 vs. 249-627mg kg(-1) As in the fronds) partially because it is more efficient in As translocation. As translocation factor (As concentration ratio in fronds to roots) was 3.0-5.6 for P. vittata compared to 0.1 to 4.8 for P. cretica. Compared to N. exaltata, P. vittata was significantly more efficient in arsenic accumulation (38-542 vs. 4.8-71 mg kg(-1) As in thefronds) as well asAs translocation (1.3-5.6 vs. 0.2-0.5). In addition, P. vittata was much more efficient in As reduction from AsV to AsIII (83-84 vs. 13-24% AsIII in the fronds). Little As reduction occurred after 1-d exposure to AsV in both species indicates that As reduction was not instantaneous even in an As hyperaccumulator. Our data were consistent with the hypothesis that both As translocation and As reduction are important for plant As hyperaccumulation.     

Glutathione synthetase promotes the reduction of arsenate via arsenolysis of glutathione

The environmentally prevalent arsenate (As(V)) undergoes reduction in the body to the much more toxic arsenite (As(III)). Phosphorolytic enzymes and ATP synthase can promote the reduction As(V) by converting it into arsenylated products in which the pentavalent arsenic is more reducible by glutathione (GSH) to As(III) than in inorganic As(V). Glutathione synthetase (GS) can catalyze the arsenolysis of GSH (γ-Glu-Cys-Gly) yielding two arsenylated products, i.e. γ-Glu-Cys-arsenate and ADP-arsenate. Thus, GS may also promote the reduction of As(V) by GSH. This hypothesis was tested with human recombinant GS, a Mg(2+) dependent enzyme. GS markedly increased As(III) formation when incubated with As(V), GSH, Mg(2+) and ADP, but not when GSH, Mg(2+) or ADP were separately omitted. Phosphate, a substrate competitive with As(V) in the arsenolysis of GSH, as well as the products of GSH arsenolysis or their analogs, e.g. glycine and γ-Glu-aminobutyrate, decreased As(V) reduction. Replacement of ADP with ATP or an analog that cannot be phosphorylated or arsenylated abolished As(V) reduction, indicating that GS-supported As(V) reduction requires formation of ADP-arsenate. In the presence of ADP, however, ATP (but not its metabolically inert analog) tripled As(V) reduction because ATP permits GS to remove the arsenolysis inhibitory glycine and γ-Glu-Cys by converting them into GSH. GS failed to promote As(V) reduction when GSH was replaced with ophthalmic acid, a GSH analog substrate of GS containing no SH group (although ophthalmic acid did undergo GS-catalyzed arsenolysis), indicating that the SH group of GSH is important for As(V) reduction. Our findings support the conclusion that GS promotes reduction of As(V) by catalyzing the arsenolysis of GSH, thus producing ADP-arsenate, which upon being released from the enzyme is readily reduced by GSH to As(III).     

The Arabidopsis thaliana aquaglyceroporin AtNIP7;1 is a pathway for arsenite uptake

We studied the effect of loss of function in the NIP subfamily II in Arabidopsis thaliana to assess their potential role(s) in arsenite (AsIII) uptake. Loss of function in AtNIP7;1 led to increased plant tolerance to AsIII and reduced total As in planta. AtNIP7;1 expression in various yeast backgrounds increased AsIII sensitivity. In the acr3Δ yeast genotype, AtNIP7;1 caused a moderate increase in AsV tolerance. Short-term As uptake in fsp1Δ expressing AtNIP7;1 was significantly larger than that in the empty vector control.

The data suggest that AtNIP7;1 can mediate AsIII transport and contributes to AsIII uptake in plants.     

Adenine nucleotide translocation in plant mitochondria

The rapid translocation of external ADP-[^14C]by corn mitochondria is inhibited by high concentrations of atractyloside with enhanced inhibition occurring in the presence of Mg²⁺. This translocation is also inhibited by AMP or ATP but CDP, GDP, IDP or UDP have little effect. Backward exchange of internal ADP-[¹⁴C] occurs in the presence of AMP, ADP or ATP but is not promoted by other nucleoside diphosphates. It is suggested that the adenine nucleotide (AdN) carrier is specific for ADP and ATP and that apparent translocation of AMP is a result of adenylate kinase activity. The translocated ADP can be separated into 3 components: (1) atractyloside-insensitive binding; (2) carrier-bound ADP saturated at ca 30 μM external ADP; and (3) exchanged ADP saturated as ca 5 μM external ADP. It is suggested that the adenine nucleotide carrier of plant mitochondria possesses similar properties to the classical carrier of vertebrate mitochondria.     

Calcium supplementation modulates arsenic-induced alterations and augments arsenic accumulation in callus cultures of Indian mustard (Brassica juncea (L.) Czern.)

In the present study, the effect of arsenate (AsV) exposure either alone or in combination with calcium (Ca) was investigated in callus cultures of Brassica juncea (L.) Czern. cv. Pusa Bold grown for a period up to 24 h. The AsV?(250 μM) + Ca (10 mM) treatment resulted in a significantly higher level of As (464 μg g^?1 dry weight (DW)) than AsV without Ca (167 μg g^?1 DW) treatment at 24 h. Furthermore, AsV + Ca-treated calli had a higher percent of AsIII (24–47%) than calli subjected to AsV treatment (12–14%). Despite this, AsV + Ca-treated calli did not show any signs of hydrogen peroxide (H₂O₂) accumulation or cell death upon in vivo staining, while AsV-exposed calli had increased H₂O₂, shrinkage of cytoplasmic contents, and cell death. Thus, AsV treatment induced oxidative stress, which in turn elicited a response of antioxidant enzymes and metabolites as compared with control and AsV + Ca treatment. The positive effects of Ca supplementation were also correlated to an increase in thiolic constituents', viz., cysteine, reduced glutathione, and glutathione reductase in AsV + Ca than in AsV treatment. An analysis of selected signaling related genes, e.g., mitogen-activated protein kinases (MAPK3 and MAPK6) and jasmonate ZIM-domain (JAZ3) suggested that AsV and AsV + Ca followed variable pathways to sense and signal the As stress. In AsV-alone treatment, jasmonate signaling was seemingly activated, while MAPK3 was not involved. In contrast, AsV + Ca treatment appeared to specifically inhibit jasmonate signaling and activate MAPK3. In conclusion, Ca supplementation may hold promise for achieving increased As accumulation in plants without compromising their tolerance.     

Influence of adenosine phosphates and magnesium on photosynthesis in chloroplasts from peas, sedum, and spinach

¹⁴CO₂ photoassimilation in the presence of MgATP, MgADP, and MgAMP was investigated using intact chloroplasts from Sedum praealtum, a Crassulacean acid metabolism plant, and two C₃ plants: spinach and peas. Inasmuch as free ATP, ADP, AMP, and uncomplexed Mg²⁺ were present in the assays, their influence upon CO₂ assimilation was also examined. Free Mg²⁺ was inhibitory with all chloroplasts, as were ADP and AMP in chloroplasts from Sedum and peas. With Sedum chloroplasts in the presence of ADP, the time course of assimilation was linear. However, with pea chloroplasts, ADP inhibition became progressively more severe, resulting in a curved time course. ATP stimulated assimilation only in pea chloroplasts. MgATP and MgADP stimulated assimilation in all chloroplasts. ADP inhibition of CO₂ assimilation was maximal at optimum orthophosphate concentrations in Sedum chloroplasts, while MgATP stimulation was maximal at optimum or below optimum concentrations of orthophosphate. MgATP stimulation in peas and Sedum and ADP inhibition in Sedum were not sensitive to the addition of glycerate 3-phosphate (PGA).

PGA-supported O₂ evolution by pea chloroplasts was not inhibited immediately by ADP; the rate of O₂ evolution slowed as time passed, corresponding to the effect of ADP on CO₂ assimilation, and indicating that glycerate 3-phosphate kinase was a site of inhibition. Likewise, upon the addition of AMP, inhibition of PGA-dependent O₂ evolution became more severe with time. This did not mirror CO₂ assimilation, which was inhibited immediately by AMP. In Sedum chloroplasts, PGA-dependent O₂ evolution was not inhibited by ADP and AMP. In chloroplasts from peas and Sedum, the magnitude of MgADP and MgATP stimulation of PGA-dependent O₂ evolution was not much larger than that given by ATP, and it was much smaller than MgATP stimulation of CO₂ assimilation. Analysis of stromal metabolite levels by anion exchange chromatography indicated that ribulose 1,5-bisphosphate carboxylase was inhibited by ADP and stimulated by MgADP in Sedum chloroplasts.

The appearance of label in the medium was measured when [U-¹⁴C] ADP-loaded Sedum chloroplasts were challenged with ATP, ADP, or AMP and their Mg²⁺ complexes. The rate of back exchange was stimulated by the presence of Mg²⁺. This suggests that ATP, ADP, and AMP penetrate the chloroplast slower than their Mg²⁺ complexes. A portion of the CO₂ assimilation and O₂ evolution data could be explained by differential penetration rates, and other proposals were made to explain the remainder of the observations.

     

Effects of nitric oxide donor, isosorbide dinitrate, on energy metabolism of rat reticulocytes

Since nitric oxide (NO) in many cells is involved in energy metabolism, the aim of this study was to evaluate the role of isosorbide dinitrate (ISDN), a NO donor, in energy metabolism of rat reticulocytes, particularly due to their high content of hemoglobin--an effective scavenger of NO. Rat reticulocyte-rich red blood cell suspensions were aerobically incubated in the absence (control) or in the presence of different concentrations of ISDN. ISDN decreased total and coupled oxygen consumption (p<0.05) while increased uncoupled oxygen consumption (p<0.05) in a dose- and time-dependent manner. This was followed by enhancement of glycolysis, as measured by increased glucose consumption and lactate accumulation (p<0.05). Levels of all glycolytic intermediates in the presence of ISDN indicate only stimulation of pyruvate kinase activity. ISDN did not alter the concentration of ATP, while increased ADP and AMP levels (p>0.05). In rat reticulocytes under steady-state conditions, 95.4% of overall energy was produced by oxidative phosphorylation but only 4.6% by glycolysis. Due to a reduced coupled oxygen consumption in the presence of ISDN, ATP production via oxidative phosphorylation was significantly diminished. A simultaneous increase of glycolytic ATP production is not enough to ensure constant ATP production. The calculated mean ATP turnover time was prolonged by 199% in the presence of 1.5 mmol/l ISDN. In conclusion, ISDN a) inhibited total and coupled respiration but enhanced uncoupled respiration, b) stimulated glycolysis, c) decreased ATP production and d) prolonged ATP turnover time in rat reticulocytes. These effects were mediated by NO as the effector molecule.     

Response of adenine and pyridine metabolism during germination and early seedling growth under arsenic stress in Brassica juncea

Adenine and pyridine nucleotides play vital roles in virtually all aspects of plant growth. This study analyzed the response of adenine and pyridine metabolism during germination and early seedling growth (ESG) of Brassica juncea exposed to two doses of arsenate (AsV), 100 and 250 μM, having non-significant or significant inhibitory effects, respectively, on germination and ESG. The ratio of NAD/NADP and NAD/NADH showed no significant change in control and 100 μM AsV, but increased significantly at 250 μM AsV during initial 24 h and also at 7th day. The activity of enzymes of NAD metabolism, viz. NAD kinase, NADP phosphatase, nicotinamidase and poly(ADP-ribose) polymerases showed significant change mostly at 250 μM AsV. Further, significant decrease was observed in the ratio of ATP/ADP and in the activities of adenylate kinase and apyrase at 250 μM AsV at 7th day. External supply of ATP (1 mM) to 100 and 250 μM AsV significantly improved germination percentage and germination strength of the seeds as compared to AsV treatments alone. The study concludes that with the increase in concentration of AsV, the balance of NAD/NADP, NAD/NADH and ATP/ADP and the activities of enzymes of adenine and pyridine metabolism were significantly altered and that these changes may be responsible for inhibitory effects of AsV on germination and ESG.     

Polynucleotide Phosphorylase Functions as Both an Exonuclease and a Poly(A) Polymerase in Spinach Chloroplasts

The molecular mechanism of mRNA degradation in the chloroplast consists of sequential events including endonucleolytic cleavage, the addition of poly(A)-rich sequences to the endonucleolytic cleavage products, and exonucleolytic degradation by polynucleotide phosphorylase (PNPase). In Escherichia coli, polyadenylation is performed mainly by poly(A)-polymerase (PAP) I or by PNPase in its absence. While trying to purify the chloroplast PAP by following in vitro polyadenylation activity, it was found to copurify with PNPase and indeed could not be separated from it. Purified PNPase was able to polyadenylate RNA molecules with an activity similar to that of lysed chloroplasts. Both activities use ADP much more effectively than ATP and are inhibited by stem-loop structures. The activity of PNPase was directed to RNA degradation or polymerization by manipulating physiologically relevant concentrations of P(i) and ADP. As expected of a phosphorylase, P(i) enhanced degradation, whereas ADP inhibited degradation and enhanced polymerization. In addition, searching the complete Arabidopsis genome revealed several putative PAPs, none of which were preceded by a typical chloroplast transit peptide. These results suggest that there is no enzyme similar to E. coli PAP I in spinach chloroplasts and that polyadenylation and exonucleolytic degradation of RNA in spinach chloroplasts are performed by one enzyme, PNPase.     

Effects of exogenous donor of nitric oxide-sodium nitroprusside on energy production of rat reticulocytes

The effects of the sodium nitroprusside (SNP), a nitric oxide (NO) donor clinically used in the treatment of hypertensive emergencies on the energy production of rat reticulocytes were investigated. Rat reticulocyte-rich red blood cell suspensions were aerobically incubated without (control) or in the presence of different concentrations of SNP (0.1, 0.25, 0.5, 1.0 mM). SNP decreased total and coupled, but increased uncoupled oxygen consumption. This was accompanied by the stimulation of glycolysis, as measured by increased glucose consumption and lactate accumulation. Levels of all glycolytic intermediates indicate stimulation of hexokinase-phosphofructo kinase (HK-PFK), glyceraldehyde 3-phosphate dehydrogenase (GAPD) and pyruvate kinase (PK) activities in the presence of SNP. Due to the decrease of coupled oxygen consumption in the presence of SNP, ATP production via oxidative phosphorylation was significantly diminished. Simultaneous increase of glycolytic ATP production was not enough to provide constant ATP production. In addition, SNP significantly decreased ATP level, which was accompanied with increased ADP and AMP levels. However, the level of total adenine nucleotides was significantly lower, which was the consequence of increased catabolism of adenine nucleotides (increased hypoxanthine level). ATP/ADP ratio and adenylate energy charge level were significantly decreased. In conclusion, SNP induced inhibition of oxidative phosphorylation, stimulation of glycolysis, but depletion of total energy production in rat reticulocytes. These alterations were accompanied with instability of energy status.     

Arsenite and arsenate impact the oxidative status and antioxidant responses in Ocimum tenuiflorum L

Physiology and Molecular Biology of Plants - Biochemical responses of Ocimum tenuiflorum plants were studied upon exposure to arsenite (AsIII) and arsenate (AsV) for 1 to 10&nbsp;d. Plants...     

The pathway of adenylate catabolism in Azotobacter vinelandii. Evidence for adenosine monophosphate nucleosidase as the regulatory enzyme.

Cell-free, dialyzed extracts from Azotobacter vinelandii rapidly dephosphorylate [U-14C]ATP to labeled ADP and AMP, which is then degraded to hypoxanthine, the end product of AMP catabolism under the experimental conditions which were used. The intermediates of the pathway from ATP to hypoxanthine have been identified by thin layer chromatography and quantitated by the 14-C content. The concentrations of intermediates present during the production of hypoxanthine are consistent with AMP nucleosidase being responsible for AMP degradation in these extracts. This result was confirmed in experiments which utilized rabbit antibody prepared against purified AMP nucleosidase. The antibody inhibited AMP nucleosidase activity in cell-free extracts but did not inhibit adenine demanase or adenosine deaminase from the same extracts. In the presence of antibody prepared against purified AMP nucleosidase, the dialyzed extracts showed a marked reduction in the production of hypoxanthine from ATP. Other enzymes which could be responsible theoretically for the conversion of AMP to hypoxanthine were not detected by standard assay procedures. These results are consistent with AMP degradation proceeding by way of AMP nucleosidase to yield adenine and ribose 5-phosphate. The adenine is then converted to hypoxanthine by adenine deaminase. Both of these enzymes were present in sufficient quantities to account for the observed rates of hypoxanthine formation. The rate of hypoxanthine formation decreases during the time course of the [U-14-C]ATP degradation experiments, even though the concentration of AMP remains high. This decrease in the rate of hypoxanthine formation as a function of time is attributed to the decreasing ATP and increasing P0-4 concentrations, since ATP is an activator of AMP nucleosidase and P0-4 is an inhibitor. These observations suggest that the in vivo activity of AMP nucleosidase could also be regulated by changes in the relative ratios of ATP:AMP:P0-4.     

Dual activity of certain HIT-proteins: A. thaliana Hint4 and C. elegans DcpS act on adenosine 5′-phosphosulfate as hydrolases (forming AMP) and as phosphorylases (forming ADP)

Histidine triad (HIT)-family proteins interact with different mono- and dinucleotides and catalyze their hydrolysis. During a study of the substrate specificity of seven HIT-family proteins, we have shown that each can act as a sulfohydrolase, catalyzing the liberation of AMP from adenosine 5′-phosphosulfate (APS or SO₄-pA). However, in the presence of orthophosphate, Arabidopsis thaliana Hint4 and Caenorhabditis elegans DcpS also behaved as APS phosphorylases, forming ADP. Low pH promoted the phosphorolytic and high pH the hydrolytic activities. These proteins, and in particular Hint4, also catalyzed hydrolysis or phosphorolysis of some other adenylyl-derivatives but at lower rates than those for APS cleavage. A mechanism for these activities is proposed and the possible role of some HIT-proteins in APS metabolism is discussed.     

Estimation of pyruvate,phosphate dikinase activity in maize leaf tissue by (phosphoenolpyruvate plus pyrophosphate)-dependent phosphorylation of AMP

Crude extracts of maize leaf tissue catalysed the phosphorylation of AMP by ³²PPi in the presence of phosphoenolpyruvate (PEP). The reaction was enhanced by F^? and NH₄⁺. The optimum concentrations of AMP, PEP and PPi were 0.3, 10 and 1 mM, respectively. Under these conditions, ca75% of the AMP phosphorylated by ³²PPi was present as ATP and ca25 % as ADP. The activity was reversibly cold labile. The specific activity of crude extracts in the presence of F^? was proportional to enzyme concentration only at protein concentrations < 25,μg/ml. Partially purified pyruvate, phosphate dikinase (PPD) from maize leaf quantitatively phosphorylated AMP to ATP in a (PEP plus PPi)-dependent reaction with the concomitant production of 0.9 mol of pyruvate per mol of AMP phosphorylated. It was concluded that (PEP plus PPi)-dependent phosphorylation of AMP provides a reliable method for estimating PPD activity in crude extracts of maize. Crude maize extracts also catalysed ³²Pi-ATP and ³²PPi-ATP exchange but these activities were not specific for PPD.     

AMP deamination delays muscle acidification during heavy exercise and hypoxia

In silico studies carried out by using a computer model of oxidative phosphorylation and anaerobic glycolysis in skeletal muscle demonstrated that deamination of AMP to IMP during heavy short term exercise and/or hypoxia lessens the acidification of myocytes. The concerted action of adenylate kinase and AMP deaminase, leading to a decrease in the total adenine nucleotide pool, constitutes an additional process consuming ADP and producing ATP. It diminishes the amount of ADP that must be converted to ATP by other processes in order to meet the rate of ADP production by ATPases (because the adenylate kinase + AMP deaminase system produces only 1 ATP per 2 ADPs used, ATP consumption is not matched by ATP production, and the reduction of the total adenine nucleotide pool occurs mostly at the cost of [ATP]). As a result, the rate of ADP consumption by other processes may be lowered. This effect concerns mostly ADP consumption by anaerobic glycolysis that is inhibited by AMP deamination-induced decrease in [ADP] and [AMP], and not oxidative phosphorylation, because during heavy exercise and/or hypoxia [ADP] is significantly greater than the Km value of this process for ADP. The resultant reduction of proton production by anaerobic glycolysis enables us to delay the termination of exercise because of fatigue and/or to diminish cell damage.     

Does AMP participate in photosynthetic phosphorylation?

Osmotically disrupted chloroplasts catalyze a rapid, light and AMP and ATP dependent ³²P_i incorporation into ATP. Light does not stimulate [¹⁴C] AMP incorporation into ATP in this system. AMP in the presence of P_i inhibits electron flow in a manner analogous to ADP inhibition in the absence of P_i. The inhibition of AMP + P_i is reversed on addition of ADP.     

Arsenic Toxicity in Soybean Plants: Impact on Chlorophyll Fluorescence,Mineral Nutrition and Phytohormones

Journal of Plant Growth Regulation - Arsenic (As) is naturally present in soils and groundwater in agricultural areas, mainly in the form of arsenate (AsV) and arsenite (AsIII). It can enter...