Extended Essay

Is there a relationship between the arsenic concentration in rice and the origin of the rice grain?

Name: Adam Costa

I.B. Candidate Number: 000534-062

School: DeLand High School

Date: 12-12-13

Supervisor: Dr. Monroe

Word Count: 3,846

Abstract

Rice is grown under conditions that are conducive to the effortless absorption of water, and its dissolved contents, into the rice plant’s membranes. Eventually, the water and its contents reach the grain of the rice plant. Therefore, aqueous inorganic arsenic has the tendency to be readily absorbed into the rice plant’s roots and stem along with the water that it is dissolved in. This possibility leads to the questioning of there being a reasonable relationship between the arsenic concentration in rice grain and the origin of the rice grain. The previously mentioned potential for there to be a one-to-one correlation between the arsenic concentration found within rice grains and the rice grains’ location of origin leads to the plausible hypothesis that the aqueous inorganic arsenic in the irrigation waters for the rice crop will transcend the plants’ membranes, until the concentration of inorganic arsenic in the irrigation waters and in the plants’ membranes come to equilibrium. In the case of this investigation, the rice subspecies were altered between each experimental trial (independent variable). The quantity recorded during this investigation consists of the arsenic concentrations determined during this investigation’s experiment (dependent variable). These experimentally yielded values were compared with arsenic concentrations determined in professional field studies, with the intent of defining the relationship between the arsenic concentrations found within the rice grains and the arsenic concentrations found in the soil from where the rice grains originated from. The contrary to the proposed hypothesis was discovered, as displayed by the accrued results: high arsenic concentrations found within rice grains were associated with locations of origin that correlated with low arsenic concentrations and vice-versa.

Word Count: 271

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Table of Contents

Introduction................................................................................................................pgs. 2-3

Determination............................................................................................................pgs. 3-4

Research Question.....................................................................................................pg. 4

Hypothesis..................................................................................................................pgs. 4-5

Methodology..............................................................................................................pgs. 5-7

Calibration......................................................................................................pgs. 5-6

Experiment.....................................................................................................pgs. 6-7

Results and Analysis..................................................................................................pgs. 7-8

Arsenic Concentrations in Rice Grain...........................................................pg. 7

Arsenic Concentrations at the Locations of Origin of Rice Grains...............pgs. 7-8

Conclusion.................................................................................................................pgs. 8-9

Evaluation and Further Investigation.........................................................................pgs. 9-10

Bibliography..............................................................................................................pgs. 10-11

Appendix....................................................................................................................pgs. 12-14

Appendix I.....................................................................................................pg. 12

Appendix II....................................................................................................pg. 13

Appendix III...................................................................................................pg. 14

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Introduction

Rice (genus Oryza. O. sativa) is one of the most consumed, if not the most consumed, grain, nonetheless food product, in the world. For more than half of the world’s population rice is an ever growing and permanent stable, with more than 90% of the world’s rice being consumed in Asia. (4)(6) With such an enormous base of consumption, this grain has become increasingly subsided by major countries. India provides an excellent example of a nation that has built on the name of rice and has made it readily available to it poorest households.

With so much of the world relying on this grain, we call rice, the conditions and status of this most important consumable must be kept in check. Given this fact, the world’s health and safety organizations have taken measures to ensure the safe and secure growth, cultivation, and distribution of rice. Among one of the analytical techniques employed by these international health and safety organizations, and one that has surprised the world over, is the determination of arsenic in all variants of rice.

Arsenic is known as a potent carcinogenic element, so it would be no surprise that international health and safety organizations were to ensure that the world’s most consumed food stuff would be free from cancer causing substances, specifically arsenic. With the inevitable discovery of arsenic in rice, I say inevitable because of the conditions rice irrigation waters have been placed under (tin mining; fertilizers and insecticides; poor sanitation; and natural evolution of inorganic arsenic into water reserves, aquifers, and water tables.), came the increased coverage; analysis; and research into the origins, interactions, and concentrations of arsenic in rice.

These precursors led the determination of the final decision on how this research, experiment, and paper were to be composed. A decided topic and question that was reasoned to be pertinent, yet given limited coverage referring to heavy metals in rice and the risks associated with this was resolved to be an evaluation of the relation between polished white rice grains and their region (soil) of origin.

The method of determination of the concentrations of arsenic in rice samples boils down to Beer’s Law. This law, in its essence, states that the transmission of light through an object is dependent upon the absorption coefficient of an object or substance. The absorption coefficient is based upon the molar absorptivity of the substance and the molar concentration of the substance.

An understanding of whether the arsenic content in the rice grain is directly correlated to the arsenic content of its origin or not would allow for the comprehension of whether the arsenic content in rice irrigation water truly matters, in the sense of rice contamination by heavy metals. This knowledge would lead to an understanding of one of two possibilities. One such possibility would be that the arsenic content of the rice grain is not correlated to the arsenic content of the origin of the rice grain. In this case, rice species and genetic predispositions for arsenic uptake would be taken into consideration as a determinate of how much arsenic would be concentrated within a single grain of rice. The second of the two possibilities would be that the rice grain and

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origin arsenic concentrations would be of mirroring relation, and in this case, the origin of the rice would be considered when regarding the concentrations of arsenic contained within a grain of rice.

Determination

There are varying ways of determining the presence of arsenic in solutions, compounds, or substances, such as the liberation of arsenic by acid digestion and analysis by flame Atomic Absorption Spectroscopy, Silver Diethyldithiocarbamate Colorimetric analysis, Inductively Coupled Plasma-Mass Spectrometry, and Hydride Generation Atomic Absorption analysis. (10)(14)(17) In the case of this experiment, the Gutzeit reaction was chosen as the method of choice when it came to the determination and analysis of inorganic arsenic species. The reason for the decision to utilize the Gutzeit reaction for this experiment lies in how many iterations, tests, and evaluations it has undergone from its initial usage in 1836 to its contemporary usage. (13) Modern iterations of this reaction have become immensely more quantitative, accurate, and require more readily available equipment and reactants.

This reaction begins with the evolution of hydrogen gas in a solution of aqueous inorganic arsenic. In the case of this experiment, sodium borohyride and sulfamic acid were utilized for the evolution of hydrogen gas. Given sodium borohyride and sulfamic acid’s tendency to favor stronger bonds that transpose hydrogen, they are constituted along the lines of being strong acids, which is ideal for the evolution of hydrogen gas for this experiment. Then, the aqueous arsenious acid reacts with the evolved hydrogen gas to yield arsine gas. Following, the arsine gas reacts with mercuric bromide. The original reaction employed silver nitrate as the reagent that would react with the arsenuretted hydrogen, which led to this reaction becoming rather expensive to conduct. An alternative reagent soon replaced silver nitrate (mercuric bromide), which yields a colored compound ranging from bright yellow to black, depending on the concentration of arsenious acid.

Production of hydrogen from sodium borohydride and sulfamic acid:

NaBH4 (s) + H3NSO3 (s) + 3H2O (l) 4H2 (g) + B(OH)3 (aq) + NaH2NSO3 (aq)

Production of arsine gas from arsenious acid:

H3AsO3 (aq) + 3H2 (g) AsH3 (g)+ 3H2O

H3AsO4 (aq) + 4H2 (g) AsH3 (g) + 4H2O

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Production of yellow-through-black color:

HgBr2 (s) + AsH3 (g) H2As–HgBr (s) + HBr (g)

Research Question

Is there a relationship between the arsenic concentration in rice and the origin of the rice grain?

This question was formed through conducted research and professional consultation. Initial questions were composed with resource availability in mind. Further questions strove to investigate limitedly covered topics. Consequently, reactants and apparatuses that were not readily available and additionally had infeasible cost projections were acknowledged, and these questions were quickly omitted from consideration. Research question alternatives and thorough professional opinion were considered, resulting in the terminal research topic utilized for the basis of this investigation. Further research allowed for a narrowed and definitively worded research question with which could be sufficiently investigated; had international relevance; yet was sparsely covered, in the sense of direct experimental conduction.

Hypothesis

The outcome of this investigation is predicted to be found as a positive correlation between the concentration of arsenic found within the rice grains and the concentration of arsenic found at the location of the rice grains’ origin. With the understanding that rice plants are submerged as a condition of healthy growth and desirable grain yield, it can be concluded that the roots and stems of the submerged plants would absorb the water that submerges the plants, as a part of the plants’ method of producing food for their furthered growth and survival. Under the circumstances of this investigation, the irrigation waters for these rice plants would be laden with dissolved inorganic arsenic, and consequently, the plants would unintentionally take in the aqueous inorganic arsenic. Additionally, given that the inorganic arsenic would have been at a higher concentration within the irrigation water than the water within the plants, the inorganic arsenic would traverse the semi-permeable membranes of the plants through osmosis, thus bringing inorganic arsenic concentrations within and on the exterior of the plants to equilibrium, one-to-one ratio. The dissolved heavy metal compound would travel up the roots and stems of the plants and reach the plants’ grain (rice). The inorganic arsenic would enter the rice husks and starchy fleshes. At this stage, the arsenic would become surrounded and contained by the soft, sticky Amylopectin of the rice’s starchy flesh, thus remaining in the rice grain, until excited (boiled) out of the rice grain. With this understanding, it can be concluded that the inorganic arsenic concentrations within the plant, tantamount to that of the concentration of inorganic arsenic in the rice grain, would have a relative correspondence to the concentration of inorganic arsenic in the irrigation water from the rice grain’s place of origin.

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Methodology

Calibration

Sodium arsenate “salt” Na2HAsO4 * 7H2O was used as the compound by which the arsenator, provided by an arsenic testing kit, used for this experiment was calibrated. 312.01 g. of this salt is one mole of this salt, while 74.92 g. of 312.01 g. of this salt is one mole of arsenic in this compound. A 10 mM. solution was created by measuring 0.312 g. of the salt with an electric scale, accurate to the milligram, and adding the measured salt to a 100 mL. volumetric flask containing 100 mL. of distilled water. The resulting solution had a concentration of approximately 7.5 x105 μg L−1. of arsenic.

The solution of 7.5 x 105 μg L−1 . was diluted 15 times to 5.0 x 104μg L−1 . by taking 66.67 μL . of the 7.5 x 105 μg L−1 . solution and adding it to a 1 mL. flat-bottom centrifuge tube that contained 933.33 μL . of distilled water. 20, 40, 60, and 80 μL . of the 1 mL., 5.0 x 104 μg L−1 . stock solution were used to create four working calibration solutions with concentrations of 20, 40, 60, and 80 μg L−1 . of arsenic respectively. The 20, 40, 60, and 80 μL . of the stock solution were added to the 100 mL. sample flask provided by the test kit, which contained 50 mL. of distilled water before each individual addition of the calibration samples (Appendix I). The calibration proceeded by following the procedure provided by the test kit.

The hydrogen sulfide filter provided was placed into the hole at the bottom of the provided bung. Care was given in wiping the grasping tips of the provided stainless-steel forceps with a towel before usage. The red filter slide from the kit was filled with one piece of the red slide filter paper, while wearing latex gloves and using the stainless-steel forceps to position the filter paper onto the outline of the filter paper on the slide, to prevent the leakage of evolved sample gas. The slide was promptly slid into the top slot of the bung. The black filter slide was also filled with one piece of filter paper through the same method used with the red slide, but the filter paper used was particular to the black slide: the black slide filter paper, which was impregnated with a high concentration of mercuric bromide.

The arsenator was turned on and the black slide was slid into the slot of the arsenator, once the screen read, “insert slide.” Then, the flask filled with 50 mL. of the sample was filled with one sachet of the A1 powder provided. The black slide was then expeditiously transferred from the arsenator to the bottom slot of the bung, since the timer for the reaction began on the screen of the arsenator once the black slide was removed from the slot. Then, the A2 tablet provided was dropped into the sample flask as the bung sealed the opening of the flask and contained the reaction. The recommended wait time for this reaction to occur was 20 minutes.

After the passage of these 20 minutes, the bung was removed from the flask and the black slide was removed from the bottom slot of the bung and was placed into the slot of the arsenator where the filter paper was then analyzed by the arsenator. Moments later the arsenator gave a

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reading of the concentration of arsenic in the sample through U.V.-vis. spectroscopy. The wavelength emitted from the diode of the provided arsenator ranged from 290 nm. to 320 nm.. (16) The reaction product (H2As–HgBr) of this experiment has wavelength absorption values ranging from 230 nm. to 340 nm.. (11)

The 50 mL. flask containing the reacted sample was then emptied into a waste beaker, the filters from the slides were emptied into the plastic waste bags provided, one A1 powder sachet and one A2 tablet were set out, and the sample flask was cleaned and rinsed with distilled water in preparation for next test. The calibration samples were tested from the 20 μg L−1 . to 80 μg L−1 . , and a reliability curve was created from the data recorded (Appendix II) (Appendix III).

Experiment

Approximately 40 g. of each rice type, Jasmine, Texmati, and Basmati, were measured individually using an electric balance accurate to the milligram. Each rice sample was given its own 600 mL. beaker and was poured into it. 300 mL. of distilled water was then added to each beaker, using a 100 mL. graduated cylinder. A ring stand with one ring secured 13 cm. from the top and another ring covered with an iron wire mesh was secured 10 cm. below the first ring was positioned near a Bunsen burner fuel supply and was utilized for the placement of the previously mentioned 600 mL. beakers.

One of the three beakers was selected and placed on the wire mesh on the bottom ring of the ring stand, a watch glass was placed on the rim of the beaker, and a Bunsen burner was connected to the fuel supply near the ring stand and placed to the side of the stand. The fuel supply was turned on, the Bunsen burner was ignited using a striker, the intensity of the flame was adjusted to give a clean, blue flame, and the Bunsen burner was promptly placed underneath the beaker placed on the ring stand. The water was given 10 minutes to come to a boil, the rice was given 15 minutes to cook as well as 2 minutes to cool down, resulting in a total heating time of 27 minutes.

During the course of the heating, the rice was stirred twice using a glass stirring rod once 5 minutes into the 10 minute waiting period for the water to come to a boil and once 7 minutes and 30 seconds into the 15 minute rice cooking time. Upon removal of the glass stirring rod from the water after stirring, special attention was given to the removal of as much water from the stirring rod as possible by tapping the stirring rod on the sides of the beaker, to prevent the measured contents of the beaker from being removed from the beaker and skewing the results.

After the rice had finished the cooking, the Bunsen burner’s fuel supply was cut off and the rice was given 2 minutes to cool. Then, the watch glass was tilted over the beaker to return the evaporated water that condensed on the watch glass to the beaker. The water from the beaker was then drained into a 400 mL. beaker while trying to prevent sample rice from entering the 400 mL. beaker. The rice was disposed of in a plastic waste bag that was set to the side. 50 mL. of the extracted water was poured into a 100 mL. sample flask that the arsenic test kit provided, and the experiment proceeded by following the procedure provided by the kit. The provided

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procedure was previously mentioned and can be referenced in the methodology of the calibration for this experiment.

The boiled 300 mL. from all of the samples individually yielded approximately 150 mL. of test solution, which allowed for the test to be performed three times per rice sample. The test for the rice sample that was first tested was then completed two more times, and the other rice samples were tested in this same fashion until all of the tests were completed and all of the results were recorded.

Results and Analysis

Arsenic Concentrations in Rice Grain

Arsenic concentrations in the Jasmine rice grain were found to be the highest in comparison to the other two rice grain samples, at a mean value of 10.33 μg L−1 . with a 40.006 g .rice sample. The arsenic concentration in the Texmati rice grain was found to be an intermediate concentration, at a mean value of 9.33 μg L−1 . with a 40.005 g . rice sample. The arsenic concentration in the Basmati rice grain was found to be the lowest in comparison to the other two rice grain samples, at a mean value of 3.66 μg L−1 . with a 39.998 g .rice sample.

Arsenic Concentrations (μg L−1 .)

Texmati (40.005 g.) Basmati (39.998 g.) Jasmine (40.006 g.)1 11 4 112 11 4 123 6 3 8Mean 9.33 3.66 10.33

Figure 1: Illustrated arsenic concentrations from experimental trials of the three rice grain samples as well as the sample masses and mean values.

Arsenic Concentrations at the Locations of Origin of Rice Grains

The arsenic concentrations within the Evangeline aquifer in Texas were found to result in a mean value of 8.03 μg L−1.. (3) The Evangeline aquifer resides along the southeast coast of Texas, running along the coast’s entirety. (3) The location where Texmati rice is grown resides due east of Houston, Texas: Beaumont, Texas which is located on the southeastern border between Texas and Louisiana as well as the northeastern section of the Evangeline aquifer. (12) The arsenic concentrations within shallow wells from aquifers of the Buddhamonthon sub-district of the Nakhon Chaisi district, Nakhon Pathom province and lower Chao Phraya Basin were found to result in a mean value of 11mg L−1 . or 0.011 μg L−1. (7) The Nakhon Chaisi district resides due west of Bangkok; the lower Chao Phraya Basin resides within the Bangkok city limits (207 km. radius). (1) The primary location of Jasmine rice growth resides on the southeastern portion of

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the Chao Phraya river basin in the Chachoengsao province of Thailand’s central region: Nariang sub-district. (2) The arsenic concentrations within shallow aquifers and major canals in the district of Punjab, India were found to result in a mean value of 14.06 ppb . or μg L−1 .. (5)The Punjab district of India is the primary region of Basmati rice growth. (9)

Conclusion

Based upon the results recorded during the conduction of this investigation’s experiment and the values recorded during professional field studies, it can be concluded that the developed hypothesis for this investigation was incorrect. With regard to the results, the results should not be analyzed isolated from one another. The ratios between the experimental values and field study values should be formed and appropriately compared. The numerical arsenic concentrations found during the experiment of this investigation were determined under the intention of achieving concentrations that were discernible by the experimental apparatuses. Varying masses of rice as well as varying timespans of boiling would yield varying concentrations of arsenic, given that the solvent (water) remained a constant volume, thus an ideal sample mass and boiling timespan had to be determined. This ideal mass and timespan was established through experimentation with the objective of determining the sample mass and the timespan of boiling that would yield arsenic concentrations discernible by the experimental apparatuses, whereupon the ideal sample mass was found to be 40 grams with the ideal timespan resulting to be 27 minutes.

Consequently, the exact arsenic concentrations from the rice grain’s location of origin would not numerically coincide with the arsenic concentrations experimentally yielded. The previously mentioned issue with numerical values is the reasoning behind the usage of ratios as a means of analyzing the correlation between experimental and field arsenic concentrations. The ratio correlate between the experimental arsenic concentrations and the arsenic concentrations found at the rice grain’s regions of origin are as follows: 0.26 (Basmati/ Punjab, India), 1.16 (Texmati/ Beaumont, Texas), 939.09 (Jasmine/ Nakhon Pathom, Thailand). The previously mentioned ratios signify the relation with which the experimental and field values were related to one

another with respect to the rice grain’s region of origin (ex . BasmatiPunjab , India ). The Basmati

relation communicates Basmati rice as yielding a lesser amount of arsenic with relation to the grain’s region of origin. Intermediately, the relation between the Arsenic concentrations found within the Texmati rice grain and its location of origin correlated as being the ratio of most relation. Regarding the experimental ratio values of the Jasmine rice grain and its respective region of origin, it is seen that this relation expresses the most deviation between the experimentally yielded and field yielded values given that this ratio results in an excessively large number which ,based upon the method with which experimental and field values were related, is indicative of a vastly higher valued experimental yield with reference to the yielded field value. Undoubtedly, the arsenic-concentration ratio relations between the Basmati rice grain

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and its location of origin as well as the Jasmine rice grain and its location of origin have no association to one another, thus nullifying the composed hypothesis for this investigation.

Evaluation and Further Investigations

The results and conclusion of this experiment have spurred the possibility of various secondary questions. With the understanding that the rice grain of the same species (Aromatic) demonstrated no correlation between the arsenic contained by the rice grain and their location of origin, questions can arise regarding how the individual genetic composition of the rice grain’s subspecies could contribute to a predisposition for heavy metal absorption through predefined chemical compositions of the plants’ various limbs and yielded grain. Given that rice grows with shallow roots and thrives on surface water (canals) it would be suggested to solely utilize field values that referenced canals and rivers. Unfortunately, this investigation lacked devotion to field values exclusively referencing canal values on the basis that this information was not readily available, in comparison to the greater availability of values regarding shallow wells and aquifers. Whether particular rice grain species have a predilection to absorb one heavy metal over another, cobalt; zinc; or iron uptake preferred over arsenic due to the geometric orientation in space of certain chemical species or the charge of one chemical species over another, would be intriguing to question and determine, if further investigations were to be conducted.

Additionally and as a given, it would be beneficial to the conductors of furthered investigations on this topic to utilize more sensitive and less crude methods of heavy metal concentration quantification. The quantifying apparatuses for this conducted investigation served their purpose well but involved qualitative and more error prone methods of quantifying the determination of heavy metal concentrations, such as a chromatic scale of sample yields where experimentally yielded yellow through black color intensities would be evaluated with the sample yields, whereupon the sample yields had concentration values ascribed to them. The experimentally yielded yellow through black intensities would be given the comparatively intense sample yield’s concentration value.

Amid instances that involved experimentally yielded color intensities below the provided sample yields (¿10 μg L−1 .), the provided arsenator quantified arsenic concentrations accurate to the2.0 μg L−1. with an analytical variability of 3%. (8)(15) Given that the methods and apparatuses of quantification for this investigation were scantly accurate at lower values of concentration, with regard to the amount of accuracy that can be obtained with methods such as Atomic Absorption Spectroscopy, Silver Diethyldithiocarbamate Colorimetric analysis, and Hydride Generation Atomic Absorption analysis, it can be concluded that the values acquired during this investigation should be taken with great scrutiny and furthered investigation with more sensitive equipment would be of utmost pertinence and importance. Furthermore, the significance of the mass deviation of the rice samples used for this investigation should also be acknowledged. Given that this investigation involves quantities of miniscule proportion, it would be essential to

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determine how much of a significance a one or an eight milligram deviation has on the prevalence of yielded arsenic concentrations of micrograms.

Bibliography

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2. Chaimanuskul, Kitipong, Luepol Punnakanta, Wimon Sonchaem, Pisit Sukreeyapongse, and Rungjarat Hutacharoen. "A Practice Model for Sustainable Agriculture Assessment: A Case Study of the Sustainable Cultivation of Thai Hom Mali (Jasmine) Rice in Thailand." Environment and Natural Resources 9.3 (2011): 13. Faculty of Environment and Resource Studies, Mahidol Univeristy, Nakhon Pathom. Print. 3 Oct 2013.

3. Chowdhury, Ali H, Radu Boghici1, and Janie Hopkins. "Hydrochemistry, Salinity Distribution, and Trace Constituents: Implications for Salinity Sources, Geochemical Evolution, and Flow Systems Characterization, Gulf Coast Aquifer, Texas." (2006): 108. Print.

4. Fairhurst, T. H. and A. Dobermann. "Rice in the global food supply." World 5.7,502 (2002): 454-349.

5. Hundal, H. S., Kuldip Singh, and Dhanwinder Singh "Arsenic content in ground and canal waters of Punjab, North-West India." (2008): 397. Department of Soils, Punjab Agricultural University. Print. 22 Jul 2013.

6. Khush, Gurdev S. "Origin, Dispersal, Cultivation, and Variation of Rice." Khwer Academic Publishers 35. (1997): 25. Plant Breeding, Genetics and Biochemistry Division, International Rice Research Institute. Print. 3 Oct 2013.

7. Kohnhorst, Andrew. "Arsenic in Groundwater in Selected Countries in South and Southeast Asia: A Review." 28.7 (2005): 77. Food Science and Technology Program, Mahidol University International College. Print. 22 Jul 2013.

8. Kosmos, Walter. "The evaluation of the arsenator." West Bengal India and Bangladesh Arsenic Crisis (1998): n.pag. Department of Analytical Chemistry, Graz University, Austria. Web. 25 Oct 2013. <http://bicn.com/acic/resources/infobank/dch98-12conf/paper2-3.htm>.

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9. Mathauda, S.S, H.S. Mavi, B.S. Bhangoo, and B.K. Dhaliwal. "Impact of Projected Climate Change on Rice Production in Punjab (India)." International Society for Tropical Ecology. 41.1 (2000): 1. Print. 24 Jul. 2013.

10. Mekoli, Megan Louise, "Novel Biological, Forensic, and Historical Applications of Inductively Coupled Plasma-Mass Spectrometry" (2012): 34.Graduate Theses and Dissertations. Paper 12832.

11. Parkin, Sean, Mohan S. Bharara, and David A. Atwood. "Solution and Solid-State Study of Heteroleptic Hg(II)-Thiolates: Crystal Structures of [Hg4I4(SCH2CH2NH2)4] and [Hg4I8(SCH2CH2NH3)2] n ‚nH2O." 45. (2006): 2115. Department of Chemistry, UniVersity of Kentucky, Lexington, Kentucky 40506-0055. Database. 21 Oct 2013.

12. Smyth, Douglas A. and Henry E. Prescott, Jr. "Sugar Content and Activity of Sucrose Metabolism Enzymes in Milled Rice Grain." Plant Physiol 89. (1989): 893. General Foods Technical Center, Tarrytown, New York 10591. Print. 3 Oct 2013.

13. Stringer, W. J. "Colorimetric Determination of Trace Metals in Beer and Brewing Materials." Determination of Arsenic 60.8 (1954): 250-251. Print. 23 Jul 2013

14. Stratton, Garland and H. Collins Whitehead. "Colorimetric Determination of Arsenic in Water with Silver Diethyldithiocarbamate." Journal (American Water Works Association) 54.7 (1962): 861-864.

15. Swash, Peter. "Field Evaluation of the Wagtech Arsenator." (2003): n.pag. Royal School of Mines, Imperial College, London, UK. Web. 25 Oct 2013. <http://users.physics.harvard.edu/~wilson/arsenic/measurement/field-eval-wagtech-arsenator.html>.

16. Yang, Hongying, Sukang Zhu, and Ning Pan. "Studying the Mechanisms of Titanium Dioxide as Ultraviolet-Blocking Additive for Films and Fabrics by an Improved Scheme." (2003): 3202. Center of Physics of Fibrous Materials, Dong Hua University, Shanghai 200051, China 2Division of Textiles and Clothing, Biological and Agricultural Engineering Department, University of California, Davis, California 95616. Database. 21 Oct 2013.

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Appendix I

Stock Solution Calculations

Original Solution

0.312 g salt in 100 mL solution (10 mM. solution)

μg AsL

( ppb )=0.312 g salt0.100 L

x 1mol salt312 g salt

x 1mol As1 mol salt

x 74.92 g As1 mol As

x 106 μg As1 g As

=749,200 μg L−1 As 750,000 μg L−1 As=7.5 x105 μg L−1 As

As working calibration solutions – 20, 40, 60, 75 μg L−1

75 μL of solution added to 50 mL water →75 μg L−1

∴what is original conc . of As?

75 x10−6 L xC c=50 x10−3 L x 75 μg L−1

C c=50,000 μg L−1 As

Likewise ,60 μL of solutionadded ¿50 mL water → 60 μL x50,000 μg L−1

50 x103 =60 μg L−1

¿ ,40 μL of this solution added¿50 mLwater → 40 μL x50,000 μg L−1

50 x103 =40 μg L−1

¿ , 20μL of this solutionadded ¿50 mLwater → 20 μL x 50,000 μg L−1

50 x103 =20 μg L−1

So, have to dilute 750,000 μg L−1 (7.5 x105 ) to 50,000 μg L−1(5.0 x 104) (15x dilution)

Need to take 6.67 mL of 750,000 μg L−1and make up to 100 mL

6.67 mL x 750,000 μg L−1=100 mL x Cd

Cd=6.67 x750,000 μg L−1

100=50,025 μg L−1

750,000 μg L−1 xV c=50,000 μg L−1 x1mL

V= 50,000750,000

=0.066667 mL=66.67 μL (750,000 μg L−1 Solution )+933.33 μL ( Distilled Water )=1000 μL ( 50,000 μg L−1 As Solution)=1mL ( 50,000 μg L−1 As Solution)

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Appendix II

Arsenator Calibration Yields

Prepared Arsenic Concentrations (μg L−1) Measured Arsenic Concentrations (μg L−1)20 2340 4360 6780 83

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Appendix III

0 10 20 30 40 50 60 70 80 900

10

20

30

40

50

60

70

80

90

f(x) = 1.05 x + 1.2R² = 0.996655216054963

Reliability Curve

𝑃𝑟𝑒𝑝𝑎𝑟𝑒𝑑 𝐴𝑟𝑠𝑒𝑛𝑖𝑐 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛𝑠 ( (̂−1))𝜇𝑔𝐿

Mea

sure

d

𝐴𝑟𝑠𝑒𝑛𝑖𝑐

((̂−

1))

𝐶𝑜𝑛𝑐𝑒𝑛𝑡

𝑟𝑎𝑡𝑖𝑜𝑛𝜇

𝑔𝐿

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