Authors
Keywords
Abstract
In this study, tube well water, soil, crop, and vegetable were collected from agricultural field where irrigated with arsenic contaminated water. Estimation of total arsenic and other metals and metalloids in soil, vegetable, and paddy (rice & husk) samples by using ICP-MS after microwave digestion. But arsenic species in paddy (rice + husk), rice, husk, and vegetable by IC-ICP-MS after TFA extraction.
Results show that the average arsenic concentration in contaminated soil, rice, and vegetable were 3.81, 3.62, and 5.66 times higher than the control samples, respectively. The overall observations indicated that arsenic concentration in vegetable and paddy were positively correlated with arsenic in soil. Also, for paddy arsenic concentration decreases shoot > seed (rice) > husk and in vegetables the distribution is leaf> stem > fruit.
The regression analysis was carried out between arsenic and other metals in soil samples. However, no significant co-relation was observed between As & Mn, As & Cu, As & Ni, or As & Pb. But a significant (<0.05) positive correlation found between As & Zn (r =+0.763, p = 0.027) and also a strong negative correlation was observed between As & Hg (r = -0.802, p = 0.009).
Arsenic along with Se, Mn, Cu, Hg, Pb & Ni were analyzed in rice & husk of 3 paddy samples cultivated with arsenic contaminated water. The regression analysis was carried out between arsenic and other metals. Linear regression shown negative correlation between As & Se (r= -0.999, p = 0.018), As & Pb (r = -0.992, p = 0.078) and positive correlation between As & Cu (r =+0.998, p = 0.03). But no satisfactory correction observed between As & Mn, As & Hg, and As & Ni. It has been observed selenium concentration decreases with increase arsenic concentration in both rice and husk, collected from As contaminated field in Bangladesh. This has also been observed in two vegetable samples those we had studied. All analyzed elements concentration (µg/gm) were less in “Kachu (Taro)” comparing “Data (Stem amaranth)” except arsenic. Arsenic was very high in “Kachu” comparing “Data” even though they were irrigated with same water containing arsenic 205 µg/L.
The overall conclusion from arsenic species analysis in rice, paddy (rice + husk), and some vegetables are that inorganic arsenic is the dominating species of arsenic. It appears from all four-rice analysis that inorganic arsenic is the major portion of arsenic in rice. All four-husk analysis shows only presence of inorganic arsenic. No methylated form of arsenic was found in any husk samples, but arsenic species in a paddy (rice+ husk) sample shows high inorganic arsenic (76.46%) and 19.37% DMA & 4.23% MMA. It shows presence of inorganic arsenic & DMA, and possibility of an unknown arsenic species in Lady's Finger. It was very high arsenic concentration in a vegetable named “Kachu” which grows inside soil a popular food in West Bengal-India and Bangladesh. Most interesting, its inorganic arsenic concentration is quite high, but it has no detectable amount of methylated form of arsenic and possible of an unknown arsenic species.
Rice and vegetable are the staple food for poor villagers of Bangladesh and West Bengal-India. This is true for the villagers in Kolsur gram-panchayet (G.P.) in Deganga block of North 24-Parganas district, West Bengal-India, where we studied for arsenic in soil, rice, and vegetable from 10 plots cultivated with arsenic contaminated water. From the results of total arsenic (drinking water + rice + vegetable + Pantavat (rice mixed with water) + water added for food preparation) body burden to North Kolsur villagers is 1185.0 µg for per adult per day and 653.2 µg for per child per day. Amount of arsenic coming from rice, vegetable, and water added for Pantavat and food preparation is 485 µg i.e., 41% of total for adult and 253.2 µg i.e., 38.8% for child, and from rice and vegetable 285 µg i.e., 24% of total for adult and 153.2 µg i.e., 23.4% for child (around age 10 years). Our findings show most of the arsenic coming from food is inorganic in nature. As toxicity of most of the organic arsenic compounds in food is less compared to inorganic arsenic.
Therefore, compared to worldwide arsenic consumption from food, it appears Kolsur villagers are also consuming high amount of inorganic arsenic from food and vegetable, and people appears also at risk from arsenic in food. Kolsur village is an example of many such villages in West Bengal-India and Bangladesh.
Further, products from arsenic irrigated water- soil system rich in arsenic are also coming to common marketplace far away from contaminated areas and even people who are not drinking arsenic contaminated water may get arsenic from food products produced from contaminated fields. In West Bengal-India and Bangladesh rice, vegetable, and other products are coming to cities (including Kolkata in West Bengal-India and Dhaka in Bangladesh) from villages and possibility that city people consuming arsenic contaminated products from contaminated areas cannot be ruled out.
Abbreviation: IC-ICP-MS, Ion chromatography-inductively coupled plasma-Mass spectrophotometry; FI-HG-AAS, Flow injection-hydride generation -atomic absorption spectrometry
Introduction
In West Bengal-India out of its total 18 districts in 9 districts arsenic in groundwater has been found over 50 µg/L. Total area and population of these 9 districts are 38,865 km2 and 42.7 million (approx.), respectively while the area and population of West Bengal are 88,000 km2 and 68 million (approx.). This does not mean that 42.7 million people in these 9 districts are drinking arsenic contaminated water and will suffer from arsenic toxicity, but no doubt they are at risk. In 9 affected districts of West Bengal, approximately 6 million people are drinking arsenic contaminated water at levels >50 µg/L. For arsenical skin lesions, we examined approx. 86,000 people in 7 affected districts out of 9 and 8500 (9.8%) people were registered with arsenical skin lesions. But we expect, from extrapolation of our generated data that nearly 300,000 people may have arsenical skin lesions in West Bengal-India.
State, West Bengal is prosperous in agriculture. The state has surplus food production and main crops are paddy and vegetable. Land of these 9 contaminated districts of West Bengal is very fertile and all are in recent gangetic deltaic plain. Major quantum of food production of West Bengal is coming from these 9 districts and tens of thousands of small and big diameter tube wells are in use for irrigation purpose. Plant needs a small fraction of the total water we pour to the field. Groundwater is considered to be the main source of water for agriculture and its use is increasing day by day. It has been noticed that even if surface water is available for irrigation from nearing source farmers are reluctant to use those sources if they must spend some extra money for this purpose. Except 5 months of rainy season (June-October) rest of the 7 months of the year farmers use groundwater for agriculture. Even during June to October if there are no rain farmers use groundwater.
During 1996 it has been reported1 by School of Environmental Studies (SOES), Jadavpur University, and Kolkata that from a single Rural Water Supply Scheme (RWSS), Govt. of W. Bengal in Malda district, supplying water to a few villages, and 147.8 kg of arsenic came out during a year with groundwater. Therefore, it is expected that huge quantity of arsenic is falling on agricultural land from contaminated tube wells in use for irrigation. A follow-up study was made by SOES to know how much arsenic is falling on irrigated land in one year during cultivation from all 3200 tube wells that exist in the block Deganga of North 24-Parganas2. The basis of calculation was like this: 3200 shallow tube wells of 7 cm to 10 cm diameter were used in 1997 in Deganga block for agriculture and average discharge rate was 20 m3/hr. electric / diesel pumps (average 5HP) were used. These shallow tube wells used to run in average 7 hours per day for 7 months in a year. We had analyzed 597 irrigation tube wells out of total 3200. Out of those 597 tube wells, 574 tube wells contain arsenic ≥10 µg/L. The average arsenic concentration of the 574 tube wells was 70 µg/L (range 10 -840 µg/L). A calculation was made to know how much arsenic is falling on soil from 3200 tube wells based on measurement of 574 tube wells (total analyzed) and extrapolating to 3200. The overall result shows from the block Deganga alone 6.4 tons of arsenic is falling on agricultural land in one year from 3200 agriculture tube wells. Thus, it appears that in West Bengal-India and Bangladesh a few thousand tons of arsenic is falling on agricultural land in every year.
Total arsenic contribution through food for many developed countries have been reported3. Although sea food contains mainly nontoxic organic forms of arsenic and rapidly excreted
Figure 1. Location of Madaripur district of Bangladesh, and North 24-Parganas and Medinipur districts of India
through urine, but other than sea food inorganic arsenic may be the major contribution of arsenic in many foods. A study from Canada4,5indicates that arsenic content of many foods is mainly inorganic in nature and typically in the range 65-75%. US-EPA reported that percentage of inorganic arsenic in rice, vegetables and fruits are 35%, 5% and 10% respectively6. It is reported that absorption of arsenic by plant is influenced by the concentration of arsenic in soil7.
In arsenic affected areas of West Bengal-India and Bangladesh huge quantity of arsenic is falling on agricultural land and thus it will be interesting and very important to know whether there is an increase concentration of arsenic in vegetable and crops that grow in this region.
In this paper, I will report (a) the total arsenic concentration in soil, paddy (shoot, rice and husk), vegetable (including edible root, stem, leaf, and fruit) in 10 plots of land irrigated with arsenic contaminated water, (b) arsenic species in paddy (rice + husk), rice, husk, and in vegetable (also in edible root, stem, and fruit), (c) some metals and metalloids in soil, vegetable, rice.and husk, and (d) Arsenic body burden.
Methods And Materials
Selection of study area
Demography of the State West Bengal is 18 administrative districts and North 24- Parganas is one of the districts. North 24-Parganas is one of the 9 arsenic affected districts of West Bengal-India also. In North 24-Parganas there are 22 blocks/ police stations. Each block has several Gram Panchayets (G.P.) and in each G.P., there are several villages. We have chosen Deganga block of North 24- Parganas district as our study area. The reasons are, (A) we have the detail 8785 hand tube-wells water analysis report of Deganga one of the 22 blocks of North 24-Parganas (Table 1) and also 597 irrigation tube wells report out of 3200 which were used for irrigation in Deganga block alone (Table 2), (B) Deganga block is close (about 60 km) from our institute (SOES) with good road connection, and (C) we are working in this block for a long time and have good report with the villagers. Figure 1 shows arsenic affected block of North 24-Parganas and Deganga block. Deganga block has 13-gram panchayets and groundwater of all these gram pahchayets are arsenic contaminated (>50 µg/L). Out of 13-gram panchayets (G. P.), in 11 G. Ps we have identified patients with arsenical skin lesions. We had chosen 10 fields in Kolsur (North) village of Deganga block under Kolsur gram panchayet. Table 3 shows the crops from 10 fields we had analyzed and other related information. For control study, we had chosen the district Medinipur, an area was groundwater arsenic concentration <3 µg/L; soils of the control area show arsenic in the range 5.31 µg/gm to 6.60 µg/gm (n=6). Overall information of control area is given in Table 4.
Table 1: Distribution of arsenic in tube wells water in Deganga, North 24-Parganas, West Bengal, India
Table 2: Distribution of arsenic in irrigated tube wells water in Deganga block, North 24-Parganas, West Bengal-India
Table 3: Type of crops and other information of 10 selected agricultural fields in Kolsur village of Deganga block, West Bengal, India where arsenic contaminated ground water was used for irrigation purpose.
Table 4: Overall information of control area, where groundwater contains arsenic below 3 µg/L
21 months study report
Studies had been carried for 21 months (August 1998 to April 2000). Table 5 shows the number of samples and time schedule of the whole study.
Table 5: The number of samples and time schedule of the whole study (from August 1998 to April 2000) *
Instrumental Techniques
The FI-HG-AAS was used in School of Environmental Studies (SOES), Jadavpur University, Kolkata, India
A flow injection-hydride generation -atomic absorption spectrometry (FI-HG-AAS) technique was used in our laboratory for analysis of total arsenic in water, soil, crop, and vegetable samples. The FI-HGAAS system was assembled from commercially available instruments and accessories in our laboratory. A Perkin-Elmer Model 3100 spectrometer equipped with a Hewlett-Packard Vectra computer with GEM software, Perkin-Elmer EDL System-2, arsenic lamp (lamp current 400 mA), and Varian AAS Model Spectra AA-20 with hollow-cathode As lamp (lamp current 10 mA) were used. The flow injection assembly consists of an injector, Teflon T-piece, tigon tubing and other parts for the FI system from Omni-fit UK. The peristaltic pump (VGA-76) from Varian and Minipuls-3, Gilson, Model M 312 (France) were incorporated into the FI system. Details of the instrumentation have been discussed in our earlier publications3,4. A Heraeus muffle furnace fitted with manual temperature control was used for dry ashing.
The ICP-MS was used in National Institute of Health Sciences (NIHS), Tokyo, Japan
A microwave digestion system (MDS-2100) from CEM Innovators in Microwave Technology, USA with a rotor for twelve Teflon digestion vessels HP-500, was used for sample digestion using HNO3 and H2O2.
The ICP-MS was used from Department of Environmental Chemistry, National Institute of Health Sciences, Tokyo, Japan. Estimation of arsenic and other metals and metalloids in soil, vegetable, and paddy, (rice & husk) have been carried out by ICP-MS method. Analytical results of SRM digested similarly and analyzed by ICP-MS. The instrumental conditions of this system are shown in Table 6.
Table 6: Instrumental conditions for ICP-MS
| Mobilephase | Milli-Qwater |
| Flowrate | 1mL/min |
| Infectionvolume | 20µL |
| Radiofrequency(RF) | 1300W |
| RFrefractingpower | Below5W |
| Flowofplasmagas | 15 L/min |
| FlowofCarriergas | 1.2 L/min |
| Measuringtime | 2 min |
| Peristalticpump | 0.2rps |
| Spraychambertemp. | 2°c |
The IC-ICP-MS was used from Department of U.S. Food & Drug Administration, Forensic Chemistry Center, Cincinnati, USA.
The IC-ICP-MS was used from Department of U.S. Food and Drug Administration (FDA), Forensic Chemistry Center, Cincinnati, USA. The chromatographic system used consisted of a model GP 50 ion chromatography pump (Dionex, Sunnyvale, CA, USA), AS 3500 autosampler (Thermo Separations Products, San Jose, CA, USA) and a non-metallic automated switching valve (Waters, Milford, MA, USA) with 20 µL injection loop between the Column outlet and ICP-MS nebulizer. Operation of the valve was controlled using signal relays from the IC pump.
A model PQ3 ICP-MS (VG Elemental) operating under normal multi-element tuning condition was used for chromatographic detection. Column effluent was directed to the concentric nebulizer and cooled conical spray chamber of the ICP-MS using a length (~60 em) of 0.25 mm. i.d. PEEK® tubing. An anion exchange column, Hamilton PRP-X 100 (4.6 x 150 mm), was used for separation of arsenic species.
Chemicals and Reagents
School of Environmental Studies, Jadavpur University, West Bengal, India
All reagents were of analytical grade. Distilled demonized water was used throughout. Standard arsenic solutions were prepared by dissolving appropriate amounts of As2O3 (Merck, Germany) and standard arsenic (V) Titrisol (Merck, Germany). Standard stock solutions were stored in glass bottles and kept refrigerated. Dilute arsenic solutions for analysis were prepared daily. The reducing solution was sodium tetrahydroborate (Merck, Germany) 1.5% (m/v) in 0.5% (m/v) sodium hydroxide (E. Merck, India Limited). The HCl (E. Merck, India Limited) concentration was 5M. Ashing acid suspension was prepared by stirring 10% (w/v) Mg(NO3)2. 6H2O and 1% (w/v) MgO in water until homogeneous4.
Standard reference materials were used to check the accuracy of the method. Pond Sediment NIES- 2, from the National Institute for Environmental Studies, Japan; Standard Chinese River Sediment 81-101 (of 1981); San Joaquin Soil SRM 2709, Citrus Leaves SRM 1572, Rice Flour SRM 1568a, Spinach Leaves SRM 1570a and Tomato Leaves SRM 1573a are from the National Institute of Standards and Technology (NIST), USA.
In National Institute of Health Sciences, Tokyo, Japan
All reagents were of analytical reagent grade. Milli-Q Water (Yamato Millipore filter, WT 100) was used throughout. Stock solutions (10 mg/L in water) of arsenic and other elements (Se, Cu, Zn, Pb, Mn, Ni, Hg) were prepared separately from 1000 mg/L stock standard (Cica-Merck, Kanta Chemical Co. Inc, Japan) of each element. All stock solutions were stored in polyethylene bottles and kept at 4°C. Dilute solutions (2.5, 5, 10, 20, 30, and 50 µg/L) for analysis were prepared daily.
The samples digestion was carried out with concentrated nitric acid (HNO3) (Wako Pure Chemical Industries Ltd., Osaka, Japan) and high purity hydrogen peroxide (H2O2) (Wako Pure Chemical Industries Ltd., Osaka, Japan).
Standard reference materials were used to check the accuracy of the method for multi element analysis. Rice flour SRM 1568a, Apple leaves SRM 1515, Tomato Leaves SRM 1573a, San Joaquin Soil SRM 2709, and Spinach leaves SRM 1570a are from the National Institute of Standards and Technology (NIST), USA.
In U.S. Food and Drug Administration, Cincinnati, U.S.A.
Ultrapure deionized water was used (DIW, Millipore, MA, USA). High-purity ammonium hydroxide was from Fisher Scientific (Fair Lawn, NJ, USA). Anhydrous trifluoroacetic acid (TFA) was from Sigma (St. Louis, MO, USA), and ammonium nitrate, and monobasic ammonium phosphate were from J.T. Baker (Phillipsburg, NJ, USA).
Commercial stock standards of As(III) and As(V) (1000 µg As/mL as As2O3 in 2% HCl and H3AsO4. ½ H2O in 2% HNO3, respectively) were obtained from Spex Industries (Metuchen, NJ, USA). Dimethylarsinic acid (98.0%) and disodium methyl arsenate (99%) were obtained from Chem Service (West Chester, PA, USA). The mobile phase consisted of 10 mM NH4H2PO4 and 10 mM NH4PO3 adjusted to a pH of 6.3 with NH4OH. NIST SRM 1568a rice flour was used for method validation
Sample collection and preservation
Water samples
Tube well water samples were collected in pre-washed (with 1:1 HNO3) polyethylene bottles. After collection concentrated nitric acid (1.0 ml per liter) was added as preservative. Samples, which were not analyzed immediately, were kept in a refrigerator at 4°C. Details of the collection procedure have been described in our earlier publications3,4.
Vegetable and crop samples
Vegetable and crop samples were collected from selected agricultural fields where arsenic contaminated water was used for agricultural purposes. Vegetable, crop, and plant samples were picked by hand, stored in polyethylene bags, and kept cool until processing in the lab. Samples were washed thoroughly with tap water to remove soil and other particles, and finally washed in sonicator with demonized water for several times. Prior to sample washing, plants consisting of both roots (below soil surface) and shoots (above soil surface) were separated into root, stem, leaf, and fruit as a sub samples and dry matter yields after drying at 60°C for about 72 hours. Dry samples made fine powder by Agate pestle and mortar, sieved, and stored in polyethylene bags with proper leveling at room temperature.
Soil samples
Surface soil samples and samples at different depth were collected from agricultural fields, where arsenic contaminated water was used for agricultural purposes and samples were also collected from non-arsenic contaminated agricultural fields (arsenic concentration in agricultural water was <3 µg/L). We collected four soil samples from different part of the same field and made a mixture. Samples were picked by non-metallic spoon, stored in polyethylene bags, and kept cool until processing in the lab. First soil samples were dried at room temperature and finally at 60°C for several hours. Dried samples were made fine powder by Agate pestle and mortar, sieved, and stored in polyethylene bags with proper leveling at room temperature.
Sample treatment for analysis
In SOES Laboratory
Sand bath digestion of soil samples
Approximately 0.10 to 0.50 gm of soil sample was placed in a 25cc conical flask (glass), 2 mL deionized water added, followed by 2 mL concentrated HNO3 and 1 mL concentrated H2SO4 (Analar Grade, E. Merck, India). The mouth of the flask was covered with a small glass funnel. Then it was heated on a sand bath until the fumes of SO3 evolved. When fumes of SO3 evolved, heating was discontinued and after cooling, the solution was diluted and filtered through a millipore membrane (0.45µm pore size) filtering apparatus, then adjusted to fixed volume. Standard Reference Materials (SRM) was analyzed in the same way to test the accuracy.
Dry ashing digestion of vegetable and crop samples
Approximately 0.20 to 0.70 gm of dry vegetable/ crop sample or 1.5 gm to 3.0 gm of wet/weight vegetable sample was taken into a 100 ml Borosil Conical Flask and 10 ml ashing aid [10% (w/v) Mg(NO3)2. 6H2O (Riedel-De Haenag, Seelze- Hannover, Germany) + 1% (w/v) MgO (E. Merck, Darmstadt, Germany) in deionized water] was added with continuous agitation. Then 5 mL HNO3 (40%, v/v) was added and evaporated to almost dryness on a hot plate at about 90-100°C. When the sample dried, the beakers were covered with a pre-washed watch glass and transferred to the muffle furnace2.
The following temperature program was adopted for proper ashing of the sample: 150°C for l hr, 200°C for 30 min, 250°C for 30 min, 300°C for 2 hrs, 400°C for l hr, and 450°C for 12-14 hrs. After cooling to room temperature 2 mL (10% v/v) HNO3 was added to the carbonaceous residue. The mixture was dried again on the hot plate to dryness and transferred to the furnace. The ash was subjected again to the following temperature program: 150°C for 1 hr and 30 min, 300°C for 30 min, and 450°C for 12- 14hrs. After cooling the white ash was moistened with a few drops of water, dissolved in 1-2 mL 6M HCI and filtered through a Millipore filter (0.45 µm) and finally made the proper volume with 6M HCl. Triplicate blanks and Standard Reference Materials (SRM) were-prepared following the same digestion procedure.
Microwave digestion of soil, vegetable, and crop samples in NIHS, Tokyo, Japan
Samples for digestion were weighed (0.2 gm to 0.5 gm of dry sample) in the Teflon vessel and added 2:1 v/v of nitric acid and hydrogen peroxide. The vessels were closed using the lid provided. For safety of the vessel, rupture membrane was inserted in the lid. Vessels were set in the turn table of the micro-wave digestion machine and the below settings were programmed (Table 7).
Table 7: Optimum parameters for sample digestion by microwave system
| Stages | 1 | 2 | 3 | 4 | 5 |
| Power(watt) | 80 | 80 | 80 | 0 | 0 |
| PSI | 70 | 120 | 170 | 20 | 20 |
| Time(min) | 20 | 20 | 20 | 20 | 20 |
| TAP(min) | 5 | 5 | 5 | 5 | 0000 |
Aftercoolingfor30minutes,the vesselswereopenedcarefully.Eachdigestedsolutionwastransferred quantitatively to a 10 mL volumetric flask and adjust to fixed volume with Milli-Q water.Finally, it was filtered through a Millipore membrane (0.45 µm) (CASL 45 2.5 CMD, membrane:Acetyl Cellulose)andkept in plastic container for analysis. The Standard Reference Materials(SRM)weredigestedunderthesamedigestionprocedure.
Preparation andextractionofcropandvegetablesamplesforarsenicspeciation( FDA lab, USA)
The rice and vegetable samples were grounded in an acid-washed glass mortar and pestle. A largeramount of each of the paddy sample was shipped; therefore, they were milled and sieved (0.5 mm) inamodelZM100ultra-centrifugalmill(Retsch,HaanGermany).PreparedsampleswerestoredinHDPEbottles atambienttemperaturepriortouse.
Sample (0.1-0.5gm) were mixed with 0.5-2 mL of 2M trifluoroaceticacid (TFA) and allowed to stand for 6hours at 100°C in either a 15 mL or a 60 mL capped HDPE centrifugetube. The TFA extract was allowedtocoolanddilutedtovolume(10-25 mL)withUltrapuredeionizedwater(DIW,Millipore,MAUSA).Extractswerefilteredthrougha 0.45µmNylonsyringefilterpriortoanalysisbyIC-ICP-MS.
Sample analysis
Flow injection- hydride generation-atomicabsorptionspectrometry(Fl-HG-AAS)(SOES Lab. )
The sample was injected into a carrier stream of 5M HCl by means of a six-port sample injectionvalve fittedwith a 50 µL sample loop. The injectedsample, togetherwith carriersolutionmetsubsequentlywithacontinuousstreamofsodiumtetrahydroborate.Mixingwithsodiumtetrahydroborategeneratedhydride,whichsubsequentlyenteredtheicewaterbathandthenthegas-liquid separator apparatus, which was cooled with ice-cold water. Thiscooling procedure and the design of the gas-liquid separator are more efficient than conventional FI-AAS and the possibility ofwater vapor entering the quartz cell is reduced to a great extent. Inside this apparatus a continuousflow of N2 carrier gas assists mixing and the reaction and subsequently carries hydride to the quartztube mounted in the air-acetylene flame for As measurement. Peak signals were recorded using acomputer linked to the atomic absorption spectrophotometer (AAS) that is capable of both peakheight and peak area measurement. The peak height signals were measured and the concentrationsof arsenic of the samples were measured/calculated against the standard curve. The experimentalconditionforFI-HG-AASsystemisgiven intheTable8.
Table8: Optimum-Parameters for arsenic determination by flow infection (FI) system
| Parameters | Perkin-Elmer(Model3100) | Varian(ModelSpectraAA-20) |
| LampCurrent | 400mA(EDLpowersupply) | 10mA(hollowcathode) |
| Wavelength | 193.7nm | 193.7nm |
| Slit | 0.7nm | 0.5nm |
| HClflowrate | 1.25mL/min | 1mL/min |
| HClconcentration | 5M | 5M |
| NaBH4flowrate | 2mL/min | 1.5mL/min |
| NaBH4concentration | 1.5%(w/v)in0.5%(w/v)NaOHsolution | 1.5%(w/v)in0.5%(w/v)NaOHsolution |
| Carriergas | Nitrogen | Nitrogen |
| Carriergasflowrate | 130mL/min | 50mL/min |
| Flame | Air-acetylene | Air-Acetylene |
Water Samples
Preserved water samples (in 1 mL HNO3 per liter of water) were analyzed by FI-HG-AAS againstarseniteandarsenatemixture(1:1)as thestandard.
Soil, vegetable ,andcropsamples
DigestedsampleswereanalyzedbyFl-HG-AASmethodagainstarsenateasthestandard.
Inductively CoupledPlasma-MassSpectrophotometry ( ICP-MS) (NIHSLab.,Japan)
ICP-MSAnalysis
ICP-MS is an element selective detector. Twenty microliters (20 µL) of the microwave acid digestedsample were injected into a carrier stream of Milli-Q water with a sample loop. The Chromatographicareas were measured, and the concentrations of elements were calculatedagainstthe individualelementstandardcurve.Theexperimentalconditionsof ICP-MSaregiveninTable6.
Ionchromatography-inductivelycoupledplasma-Massspectrophotometry (IC-ICP-MS) (Food& Drug Lab.,USA)
Figure 7showsthe chromatogramobtainedfora standardmixtureofAs(III),DMA,MMAandAs(V)inourexperimentalcondition(Table9).Eachofthearsenicspeciesis present at an arsenic concentration of 2 ng/mL. Data was collected for 10 minutes. The four arsenicspecies are baseline resolved in under 8.5 minutes; however, arsenobetaine (AsB) is not resolved fromAs(III) under these separation conditions.AsB is generallyfoundin fishand shellfishsamplesand isnotexpectedtobepresentinvegetableorricesamplescollectedfromarseniccontaminatedagriculturalfields.Theprecisionofpeakareasmeasuredoveraperiodof4hours(n=5)usingreplicate 25 µLinjectionsof a standardcontaining2 ng/mL eachofAs(III), DMA,MMAandAs(V)was 4.8%, 4.4%, 4.1%, and 9.0%,respectively.As estimate of the instrumentaldetectionlimit(IDL)for each ofthe arsenic specieswas calculatedbased on3 times,the standard deviation ofpeakareameasurementsforreplicate25 µl injectionsofa standardcontaining0.2ng As/mL eachofAs(III),DMA,MMAandAs(V). TheIDLswere 0.1, 0.1, 0.1and 0.2 ng/mL forAs(III),DMA,MMAandAs(V),respectively.
Table 9. IC-ICP-MS operational condition
| Column | Ananionexchangecolumn, HamiltonPRP-X100(4.6x150mm) |
| Mobile phase | 10mMNH4H2PO4,10mMNH4NO3adjustedtoapHof6.3withNH4OH |
| Flowrate | 1mL/min |
| Samplevolume | 20 µL |
| Detector | ICP-MS |
| Forward Power | 1350 w |
| Coolant Ar flow | 12 L/min |
| Auxiliary Ar flow | 1.0 L/min |
| Nebulizer flow | 0.8 L/min |
| Monitoring mass | m/z 75 |
| Sample rate | 0.5 Hz |
| Elution order of Arsenic species | As(III), DMA, MMA, As(V ) |
Sampleswere analyzedusing calibrationstandardsat 0.5,1, 2, 5 and10 ng/mL concentrations (insome cases a 20 ng/mL standardwas also used).Peakareaswere correctedfor anydriftassociatedwith the flow injection signal at the beginning of each chromatogram. The concentrations of severalsampleswerealsocheckedusingstandardaddition.
Spikes of each of the arsenic species were taken through the method and spike recoveries of 83%,88%, 100%, and 93% were obtained for As(III), As(V), MMA and DMA, respectively. However. itshould be noted that As(V) can be partially reduced during the extraction procedure.The As(V)recovery was calculated in spiked samples using the sum of the increase in the As(III) and As(V)concentrations. Because ofthis partial reduction,the methodis only capable ofprovidingtotalinorganic arsenic as the sum of the As(III) and As(V) concentrations. Standard NIST SRM 1568a RiceFlouralsoanalyzedbythesameprocedureandthesumofthe arsenicspeciesconcentrationsforSRM RiceFlour(0.27 µg/gm) comparedwellwiththecertifiedtotalarsenicvalue(0.29µg/gm).
Total arsenic in irrigation tube wells ,soil, vegetable,paddy samples were analyzed by usingFI-HG-AASafterdryashing(vegetable,rice,andhusk)andaciddigestion(soil)
Water samples used for cultivation had been collected from 10 locations and analyzed by FI-HGAAS method and their results are given in Table 10.Similarly, soil samples had
Table10:Analysisofarsenicand ironfor 10irrigationtube-wellusedin10fieldsforcultivation
| Tube wellNo. | August1998 | November1998 | May1999 | February2000 | April2000 | April2001 | ||||||
| As(µg/L) | Fe(µg/L) | As(µg/L) | Fe (µg/L) | As (µg/L) | Fe (µg/L) | As(µg/L) | Fe(µg/L) | As(µg/L) | Fe(µg/L) | |||
| F-TW1 | 700 | 4875 | - | - | 724 | 4833 | 789 | 5025 | 805 | 5358 | 827 | 5850 |
| F-TW2 | 560 | 5897 | 540 | 6792 | 579 | 6999 | 560 | 6852 | 570 | 6958 | 589 | 7600 |
| F-TW3 | 110 | 3325 | 103 | 3126 | 125 | 3602 | 135 | 3249 | 156 | 3927 | 145 | 3560 |
| F-TW4 | 460 | 7354 | - | - | 468 | 6862 | 455 | 7187 | 488 | 7771 | 475 | 7910 |
| F-TW5 | 355 | 5250 | - | - | 398 | 5027 | 452 | 4760 | 477 | 5180 | 496 | 5580 |
| F-TW6 | 200 | 4850 | 210 | 3951 | 215 | 4326 | - | - | - | - | 185 | 4180 |
| F-TW7 | 215 | 4425 | - | - | - | - | 228 | 5292 | 218 | 4720 | 238 | 4870 |
| F-TW8 | 220 | 4110 | 208 | 3680 | 215 | 3950 | 218 | 4420 | 233 | 4720 | 217 | 4900 |
| F-TW9 | 220 | 3860 | - | - | - | - | - | - | 240 | 4220 | - | - |
| F-TWl0 | 135 | 2562 | - | - | 140 | 2979 | 151 | 3200 | 195 | 3229 | 176 | 3140 |
Table 11: Analysis of arsenic in soil where arsenic contaminated groundwater was used for cultivation
Table 12: Distribution of arsenic concentration in different parts of the vegetable collected from 6 fields out of 10 irrigated with arsenic contaminated water
Table 13: Distribution of arsenic concentration in different parts of paddy plant collected from 3 selected location of Kolsur (N) in Deganga block, North 24-Parganas, West Bengal, India during monsoon period and rainwater was used for cultivation
Table 14: Distribution of arsenic concentration in different parts of paddy plant collected from 5 selected fields of Kolsur (N) village in Deganga block, North 24-Parganas, West Bengal, India during pre-monsoon period and cultivated with arsenic contaminated groundwater
Table 15: Analytical results of Standard Reference Matarial (SRM) by FI-HG-AAS
| Sample | Certified value | Found value |
| NIST,SRM1572(CitrusLeves) | 3.1± 0.3(µg/gm) | 3.5± 0.5(µg/gm) |
| NIES-2(PoundSediment) | 12.2±2(µg/gm) | 9.85 ±0.5(µg/gm) |
| ChinesRiverSediment81-101(of1981) | 56.0±10.0(µg/gm) | 53.79±2.0 (µg/gm) |
| NIST,SRM2709(SanJoaquinSoil) | 17.7±0.8(µg/gm) | 16.87±0.34(µg/gm) |
| NIST,SRM®1568a(RiceFlour) | 0.29 ±0.03(µg/gm) | 0.28±0.04(µg/gm) |
| NIST,SRM15708(SpinachLeaves) | 0.068±0,012(µg/gm) | 0.062±0.014(µg/gm) |
| NIST,SRM1573a(TomatoLeaves) | 0.112±0.004(µg/gm) | 0.100(µg/gm) |
Arsenic concentration in irrigation tube well and soil before and after a devastating flood
During September 2000 to October 2000 of our 10 experimental Fields were submerged with water due to a devastating flood. The analytical results are given in Table 16.
Table 16: Arsenic concentrationinirrigationtube wellandsoilbeforeandafteradevastatingflood
| TubewellNo./FieldNo. | Arsenicconcentrationinwater(µg/L) | Arsenicconcentrationinsoil(µg/L) | ||
| Beforeflood(April2000) | Afterflood(April2001) | Before flood(April2000) | Afterflood(April2001) | |
| FTW1/Fl | 805 | 827 | 34.15 | 18.76 |
| FTW2/F2 | 570 | 589 | 43.08 | 17.97 |
| FTW3/F3 | 156 | 145 | 17.46 | 11.23 |
| FTW4/F4 | 488 | 475 | 34.11 | 28.69 |
| FTW5/F5 | 477 | 496 | 31.95 | 24.83 |
| FTW6/F6 | - | 185 | 25.63 | 19.97 |
| FTW7/F7 | 218 | 238 | 25.54 | 22.35 |
| FTW8/F8 | 233 | 217 | 22.32 | 7.91 |
| FTW9/F9 | 240 | - | 23.67 | 8.32 |
| FTW10/FI0 | 195 | 176 | 23.41 | 18.62 |
been collectedfrom 10 fields where contaminatedunderground water was used for cultivation. The analyticalresults of those soil samples are given in Table 11.Vegetable and paddy samples (includingvarious parts) cultivated with arsenic contaminatedwater had been collected time to time fromselectedfields.TheiranalyticalresultsaregiveninTable12,13,&14,respectively.Analyticalresults ofStandardReferenceMaterial(SRM)digestedsimilarly&analyzedbyFI-HG-AASgiveninTable15.
Total arsenicandothermetalsandmetalloidsinsoil , vegetables,andpaddy(rice&husk)samplesbyusingICP-MSaftermicrowavedigestion.
Estimation of arsenic and other metals and metalloids in soil, vegetable, and paddy, (rice & husk)havebeencarriedoutbyICP-MSmethod.Totalarsenicandothermetalsandmetalloidsconcentrationsinsoil,rice(alsoinhusk),andvegetablearegiveninTable 17,18,and 19, respectively. Analytical results of SRM digested similarly and analyzed by ICP-MS giveninTable20.
Table17:Concentration(µg/gm)of 7elementsin9contaminatedsoilscollectedfromarseniccontaminatedfieldsof WestBengal-IndiaandBangladesh
| FieldNo. | Asinwater(µgrl) | Typeofsample | As | Mn | Cu | Hg | Pb | Ni | Zn |
| Fl | 805 | Soil | 34.15 | 732.9 | 58..44 | 1.13 | 67.36 | 72.29 | 80.38 |
| F2 | 570 | Soil | 43.08 | 508.20 | 49.07 | 1.13 | 52.87 | 53.76 | 105.00 |
| F3 | 156 | Soil | 17.46 | 388.33 | 38.25 | 1.36 | 39.67 | 40.48 | 58.53 |
| F4 | 488 | Soil | 34.11 | 538.68 | 54.65 | 1.20 | 52.38 | 53.71 | 70.08 |
| F6 | 215 | Soil | 25.63 | 514.93 | 49.16 | 1.26 | 57.12 | 61.44 | 68.54 |
| F7 | 218 | Soil | 25.54 | 457.46 | 46.34 | 1.47 | 40.33 | 51.12 | 45.62 |
| Fl0 | 195 | Soil | 23.41 | 415.47 | 42.60 | 1.61 | 43.87 | 44.59 | 52.12 |
| Bangladesh | 492 | Soil':I | 40.98 | 484.29 | 51.05 | 1.15 | 46.89 | 50.08 | - |
| Bangladesh | 525 | Soil' | 42.13 | 473.62 | 49.20 | 0.96 | 55.92 | 61.67 | 71.47 |
Table18:Concentration(µg/gm) of 7elementsinriceandhuskcollectedfromarseniccontaminatedagriculturalfieldsof WestBengal-IndiaandBangladesh
| FieldNo. | Arsenic inwater(µg/L) | Arsenicinsoil(µg/gm) | Sampletype | Elements | ||||||
| As | Se | Mn | Cu | Hg | Pb | Ni | ||||
| Bangladesh | 205 | 18.77 | Rice | 0.273 | 0.458 | 25.63 | 5.705 | 0.086 | 0.154 | 0.925 |
| Husk | 0.067 | 0.020 | 27.84 | 0.785 | 0.112 | 0.130 | 0.598 | |||
| F2 | 570 | 43.08 | Rice | 0.749 | 0.280 | 22.09 | 7.61 | 0.085 | 0.027 | 0.090 |
| Husk | 0.318 | 0.003 | 27.22 | 1.465 | 0.113 | 0.216 | 0.187 | |||
| F4 | 488 | 34.11 | Rice | 0.780 | 0.262 | 22.64 | 7.61 | 0.086 | 0.037 | 1.19 |
| Husk | 0.308 | BDL | 30.98 | 1.662 | 0.123 | 0.087 | 1.281 | |||
BDL:BelowDetectionLimit
Table 19: Concentration (µg/gm) of 7 elements in vegetable samples collected from arsenic contaminated agricultural fields of Bangladesh
| Field | Arsenicinwater(µg/L) | Type ofsample | Elements | ||||||
| As | Se | Mn | Cu | Hg | Pb | Ni | |||
| Bangladesh | 205 | Data*(Stempart) | 0.043 | 0.420 | 511.97 | 50.25 | 0.674 | 1.98 | 31.47 |
| Bangladesh | 205 | **Root part of an esculent edible plant | 0.729 | 0.255 | 113.35 | 22.32 | 0.513 | 0.236 | 4.21 |
*Akindofvegetable,wholeportion(stem+leaf)isusedforfoodandlocalname'Data'
**Akindofpopularvegetable,wholeportion(root+stem+leaf)isusedforfoodandlocalname 'Kachu'.
Table20:Analyticalresults of NISTStandardReferenceMaterial (SRM) byICP-MS
Arsenic species in paddy (rice+ husk), rice, husk, and vegetable by IC-ICP-MS after TFA (trifluoroacetic acid) extraction
The analytical results are given in Tables 21 and 22.
Table 21: Concentration of arsenic species (ng/gm) and percentage of inorganic arsenic and methylated arsenic in rice, husk, paddy (rice+ husk) & vegetable (dry) collected from arsenic contaminated fields in Kolsur (N) village of Deganga block, North 24-Parganas, West Bengal, India
Table 22: Concentration of arsenic species (ng/gm) and percentage of inorg-As and methylated arsenic in paddy (rice+ husk) and vegetable (dry) collected from arsenic contaminated fields in Datterhat village of Madaripur district, Bangladesh
Results & Discussion
Table 10 shows analysis of arsenic from August 1998 to April 2000 of 10 tube wells used in 10 fields for irrigation purpose. Although from the results of arsenic in tube wells it appears that in someof the tube wells there is increase of arsenic with time but this type of variation, we had experienced in many tube wells during our work in West Bengal-India and Bangladesh.
It has also been observed that arsenic concentration in same field varies locations to location (Table 23) and concentration of arsenic is higher at the surface than at any depth (Table 24 and Figure 2). Table 24 and Figure 2 indicate that arsenic concentration is higher at surface and at depth 18-inch and 36-inch the variation is minimum.
Table 23. Distribution of arsenic concentration (µg/gm) of soil samples collected from different location of the same arsenic contaminated fields during August 1998.
Table 24. Distribution of arsenic concentration (µg/ gm) in contaminated soil with depth
Figure 2: Distribution of arsenic concentration (µg/ gm) in soil with increasing depth (in inch.).
Table 16shows arsenic concentration in irrigation tube wells and soil measured in April 2000and again in April 2001 after flood. Our 21 months study on arsenic in soil, crop, and vegetable finished duringApril 2000.However, during September 2000 - October 2000 there was a devastating flood in WestBengal.MostofthepartsofNorth24-Parganasincludingour10experimental
fieldsweresubmerged in floodwater.During April 2001 we went to the fields and collected water and soilsamples from the same location of our experimentalfields. Table 16indicates that there isalmost no change of arsenic in irrigation tube well, but drastic change of arsenic in soil. Thus, itappears that arsenic from soil after flood washed away but six months was not sufficient for aquiferdilution.
Table 25shows arsenic concentration in rice & husk (a) cultivated with arsenic contaminatedunderground water &elevatedarsenic concentration in soil, (b) cultivated with rainwater & arsenicconcentrationinsoilislow, and(c)controlledcultivation:cultivatedbygroundwaterhaving arsenic<3 µg/Landsoilarsenicconcentration5.31-6.13µg/gm.FromtheTable25itappearsthathigher the arsenic concentration in irrigation water &soil, higher is the arsenic concentrationin rice &husk.In pre-monsoon cultivation paddy was grown in arsenic rich irrigated water with elevatedarsenic in soil. But in monsoon cultivation, contribution of arsenic from water for irrigation was notthere.So,alsoarsenicinsoilhasgonedownasrainwaterwashedawaysome arsenicfromsoil. It shows that the average arsenic concentration in contaminated soil, rice, and vegetable were 3.81, 3.62, and 5.66 times higher than the control samples, respectively.
Estimation of arsenic in different parts of the vegetable & paddy had also been carried out to knowthe distribution of arsenic in stem, leaf, and fruit for vegetable and shoot, rice, &husk for paddy.Analyticalresultsoffew are representedin Tables12-14. Table 13is the arsenic concentrationin paddy irrigated with rainwater (monsoon) and Table 14is for paddyirrigatedwitharseniccontaminatedgroundwater (pre-monsoon).
The overall observations from Tables 12-14are arsenic concentration invegetable and paddy increases when arsenic in soil is higher and when cultivated with arseniccontaminated groundwater.Also, for paddy arsenic concentration decreases shoot > seed (rice) >husk and in vegetables the distribution is leaf> stem >fruit.Although it is reported8that rootcontains maximum amount of arsenic, but we could not analyze root for paddy plant as we were notsure about adhered soil remove from root.Arsenic in different parts of paddy with increasingconcentration of arsenic in soil is given in Figures 3(pre-monsoon andhigher concentration of arsenic in soil) & Figure 4(monsoon andarsenicconcentrationinsoilislow)and that of vegetable given inFigure5.
Figure 3: Distribution of arsenic in different parts of paddy (pre-monsoon) with increasing arsenic concentration in soil.
Figure 4: Distribution of arsenic concentration in different parts of paddy (monsoon) with increasing arsenic concentration in soil.
Figure 5: Distribution of arsenic concentration in different parts of vegetable with increasing arsenic concentration in soil.
Arsenic analysis of few rice and vegetable samples were done from different laboratories. Results are given in Tables 26-28. FI-HG-AAS after Teflon bomb digestion was done from our laboratory; microwave digestion followed by ICP-MS was done from National Institute of Health Sciences (NIHS) laboratory, Tokyo, Japan & IC-ICP-MS for various species done from US Food and Drug Administration Laboratory, Forensic Chemistry Center, Cincinnati, USA. Results of IC-ICP-MS represents only sum of inorganic arsenic (In-As) + MMA + DMA. It is expected IC ICP-MS results will be low compared to FI-HG-AAS & ICP-MS results after digestion.
Table 26: Arsenic concentration in same rice and paddy (rice+ husk) samples measured by using FI-HG-AAS and IC-ICP-MS in different laboratories.
Table 27: Arsenic concentration in same rice and paddy (rice+ husk) samples (contaminated) measured by using FI-HG-AAS and IC-ICP-MS in different laboratories.
Table 28: Arsenic concentration in same vegetables samples measured by using FI-HG-AAS, ICP-MS, and IC-ICP-MS in different laboratories.
Total arsenic and other metal and metalloid in soil, vegetable, and paddy in some samples of West Bengal-India and Bangladesh
Along with arsenic in soil samples (n = 9), Mn, Cu, Hg, Pb, Ni & Zn were analyzed by ICP-MS after microwave digestion (Table 17). Our analysis of NIST soil sample (Table 20) by the same procedure is in well agreement. The regression analysis was carried out between arsenic and other metals. However, no significant positive or negative co-relation was observed between As &a
