Mitigation and Remedy of Groundwater Arsenic Menace in India

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Mitigation and Remedy of Groundwater Arsenic Menace in India : A Vision DocumentChapter -1Arsenic: Source, Occurrence and GeochemistryArsenic that has the symbol 'As', and atomic number 33, atomic weight 74.92 is oftenreferred to as a metal but, it is classified chemically as a nonmetal or metalloid belonging toGroup-15 of the periodic table. The most common oxidation states for arsenic are : -3(arsenides: usually alloy-like intermetallic compounds), +3 (arsenites (As(III)), and mostorganoarsenic compounds), and +5 (arsenates(As(V)): the most stable inorganic arsenicoxycompounds). Arsenic is always present as compounds with oxygen, chlorine, sulphur,carbon and hydrogen on one hand, and with lead, gold and iron on the other. It can exist ininorganic or organic form; inorganic arsenic is generally more toxic than organic arsenic.Inorganic arsenic occurs naturally in many kinds of rocks and it is most commonly found withsulfide ores as arsenopyrite. Inorganic arsenic compounds are known to be human carcinogens.Arsenic combined with carbon and hydrogen is classified as organic arsenic. Both inorganic andorganic compounds are typically white to colorless powders. Arsenic in element form isinsoluble in water. It is soluble in oxidized from.Arsenic is found in the natural environment in abundance in the Earth's crust and insmall quantities in rock, soil, water and air. The average concentration of arsenic in thecontinental crust is 1-2 mg/kg. The mean concentration of arsenic in igneous rocks ranges from1.5 to 3.0 mg/kg, whereas in sedimentary rocks it ranges from 1.7 to 400 mg/kg. About one thirdof the arsenic in the atmosphere comes from natural sources. Volcanic action is the mostimportant natural source of arsenic. The next most important natural source is thearsenic-containing vapor that is generated from solid or liquid forms of arsenic salts at lowtemperatures. The rest two third comes from man-made sources. Mining, metal smelting,burning of fossil fuels and coal-fired powder plants are the major industrial processes that contributearsenic contamination to air, water and soil. Elemental arsenic is producedcommercially from arsenic trioxide. Arsenic trioxide is a by-product of metal smeltingoperations. Environmental contamination also occurs from pesticides used in agriculture andfrom chemicals used for timber preservation. About 70% of the world production of arsenic isused in timber treatment, 22% in agricultural chemicals, and the remainder in glass,pharmaceuticals and metallic alloys. Thus, the sources of arsenic can be categorized as: (i)geological (geogenic), (ii) anthropogenic (human activities), and (iii) biological (biogenic). Figure-1.1 depicts a schematic diagram of major sources and routes of arsenic in soil and aquaticecosystem. Important arsenic bearing minerals are given in Table-1.1, in which, the mostcommon is Arsenopyrite (FeAsS).NIH & CGWB 1
Arsenic: Source, Occurrence and GeochemistryGeogenicGeothermal/Volcanic activitiesWeathering of rocks & mineralsPesticides, herbicidesAgricultureSeed treatmentCattle dipFertilizerTimber treatmentAsAnthropogenicIndustrialTanneryElectro plasticPaints and ChemicalsOthersSewageSmeltingPlantsBiogenicAgricultural organisms/ Micro‐aquatic biotaFigure 1.1: Major sources and routes of Arsenic in soils and aquatic ecosystem( Source : Donald L. Sparks, 2005)Table 1.1: Important Arsenic Bearing MineralsMineral Arsenic content (%)Arsenopyrite (FeAsS) 46Lollingite (FeAs 2 ) 73Orpiment 61Realger 70Native Arsenic 90 – 1002NIH & CGWB
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Mitigation and Remedy of Groundwate
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5.2.2 Co-precipitationMitigation an
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5.8 SummaryMitigation and Remedy of
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Mitigation and Remedy of Groundwater Arsenic Menace in India

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