Arsenic Hot Spots Detected in the State of Bihar
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Annual Conference 2007, Royal Geographical Society, London Session key: BSG-session 3 29-31 August, 2007 Paper-5 Arsenic contaminated aquifers: a study of the Ganga levee zones in Bihar, India A.K.Ghosh1. S.K..Singh2, Nupur Bose3, S. Chaudhary4 1 Department of Environment and Water Management, A.N.College, Patna 2 Department of Environment and Water Management, A.N.College, Patna 3 Department of Geography, A.N.College, Patna, India 4 Department of Botany, T.M.Bhagalpur University, Bhgalpur, India ABSTRACT- 'In Bihar Plains, ground water is the most important source of drinking and irrigation water. The purpose of this interdisciplinary study, undertaken along the levee of river Ganga in the Mid Ganga Plain, was to determine the existence and intensity of arsenic contamination in aquifers being tapped for direct and indirect ingestion of the properties of the region’s ground water, in the four districts of Bihar [India], i.e., Patna, Bhojpur, Vaishali and Bhagalpur. The methodology involved formulation of a protocol for arsenic detection in ground water, use of Field Test Kits for initial detection, obtaining GPS coordinates of arsenic hotspots for spatial analysis of the problem, and confirmatory testing of arsenic hot samples by U.V., and Atomic Absorption Spectrophotometry. Water samples of 28000 private and government owned hand pumps were tested. Many arsenic hotspots were detected in all the four districts, the coordinates of which were recorded by GPS. Arsenic contamination up to 1861 ppb. was found in the western district of Bhojpur, against the W.H.O. permissible limit of 10 ppb. The greatest frequency of contaminated hand pumps was noted in the eastern district of Bhagalpur. Sharp spatio- temporal variations of contamination levels were detected in this densely populated study belt. Introduction Arsenic is one of the less abundant metalloids forming the earth’s crust. Its important physico-chemical characteristic is that it is commonly concentrated in sulphide-bearing mineral deposits, pyrites and hydrous iron oxides1,2. Its presence in ground water sources is attributed to a number of natural and anthropogenic causes, based on its property of solubilizing in ground waters “depending on pH, redox conditions, and temperature and solution composition”3. Main sources of arsenic in aquifers include organic carbon or black shales, Holocene alluvial deposits, and volcanic sources4. Of particular relevance to this study, is the “strongly reducing, arsenic- rich aquifers”5 of the young alluvial sediments of the Mid Ganga Plains. Arsenic occurs widely in aquifers of deltaic sediments6, near zones of orogeny, and in deep sandy aquifer layers7 as fluvial deposits. It is introduced into the aquifer sediments in soluble state and gets adsorbed on iron-rich clastic grains and authigenic siderite concentrations. The adsorption process and its consequent desorption are stated to be controlled by microbial activity within the concerned aquifers8. Sediments containing 1 to 20 ppb. of arsenic can give rise to high dissolved arsenic of >50 ppb. by one or both of two possible causes – an increase of pH of over 8.5 or the onset of reductive iron dissolution3. Also, presence of solutes can also decrease or prevent the adsorbtion of arsenate and arsenite ions onto fine grained clays, like iron oxides8. Additional processes promoting high arsenic content in ground water are oxidation and dissolution of arsenian pyrite, Fe[As,S]2, and arsenopyrite [HN8], FeAsS9. Oxidation occurs either by infiltration of oxygenated ground waters10, or by lowering of ground water table into a stratigraphic zone of arsenic –rich sulphides11. There are two main theories as to how arsenic is released into the groundwater - Pyrite oxidation: In response to pumping, air or water with dissolved oxygen penetrates into the ground, leading to decomposition of the sulphide minerals and release of arsenic. Oxyhydroxide reduction: Arsenic was naturally transported in the river systems of Bangladesh adsorbed onto fine-grained iron or manganese oxyhydroxides. These were deposited in flood plains and buried in the sedimentary column. Due to the strongly reducing conditions which developed in the sediments and groundwater of certain parts of Bangladesh the arsenic was released into groundwater. The release mechanism is still hotly debated but the second theory is thought to be the more likely explanation. Our recent hydrochemical study of groundwater arsenic along transects from the foothill alluvium to the Indian Shield exposed in Mid Ganga Basin indicate that As concentrations are much higher in groundwater collected from the youngest alluvial terraces (~50% samples have 0.01 mg/L [WHO Maximum Contaminant Level] As, maximum 0.52 mg/L), than those associated with the shield (all 0.005 mg/L). Most (87%) of the As is present as As(III) 12. Arsenic toxicity Arsenic is highly toxic carcinogen (Category I) and also a mutagen / teratogen (harming foetus). Arsenic in ground water that is used for human consumption water, poses the greatest threat to public health13. Reliable data on exposure and health effects are rarely available, but it is clear that there are many countries in the world where arsenic in drinking water has been detected at concentrations greater than the WHO Guideline Value, 0.01 mg/L or the prevailing national standards. These include Argentina, Australia, Bangladesh, Chile, China, Hungary, Mexico, Peru, the United States of America and some countries in the South-East Asia Region. The arsenic crisis in Bangladesh has been described as one of the worst cases of mass poisoning in world history. Studies from West Bengal in India show that approximately 5 million persons are consuming groundwater containing arsenic exceeding 0.05 mg/L. Recent unconfirmed reports point to the presence of arsenic in Tamil Nadu and other states of India, implying industrial contamination of groundwater. In India, it is estimated that 220 000 of the 5 million exposed subjects are showing signs of arsenicosis. W.H.O.14 has published Guidelines for Drinking Water Quality in which a contemporary value for an acceptable maximum level of Arsenic was set at 10 ug/l/ for safe water. National standards range from 7 ug/l in Australia to 50 ug/l in Vietnam, Cambodia and Bangladesh15. Long-term oral exposure via drinking water can cause cancer of the skin16, lungs, urinary bladder, and kidneys. With long term exposure the first changes are usually seen in the skin pigments (indicator of arsenic poisoning), then hyperkeratosis. Symptoms of chronic arsenic poisoning can take five to 15 years to appear and are apparently influenced by nutrition and general health standards24. Increased risks of lung and bladder cancer and of skin lesions have been observed at arsenic concentrations of less than 0.05 mg / L of drinking water.. Statement of the problem- Naturally occurring Arsenic, as a water quality issue in South Asia, began to attract international attention in the early decade of the nineties, when widespread chronic arsenic poisoning cases became apparent in Bangladesh and later in West Bengal, India17,18. Arsenic pollution in groundwater in this part of the subcontinent is a contentious issue. Investigations into the causation of arsenic pollution require a multidisciplinary approach19. Later, the discovery of arseniferrous aquifers in Simaria-Ojhapatti village under Shahpur Block in Bhojpur, Bihar, located further upstream of the Bengal basin in 2003, raised apprehensions about the greater spatial spread of this dreaded contamination along the Ganga Valley. In 2002, School of Environmental Studies, Jadavpur University, detected arsenic levels higher than the Bengal contamination readings. This has made it urgent for further detection of Arsenic infestation in the surrounding aquifers near River Ganga, within Bihar20,21. The study area of this research incorporates Patna District, the justification being its close proximity to Bhojpur District. The two districts are separated by the River Sone which confluences with the Ganga on the northern boundaries of both Bhojpur and Patna. Based on the hypothesis of previous random water analysis about possibilities of contamination in newer fluvial deposits,22, the study area of levee region was confined to an approximate belt of 10 kms. along the southern bank of River Ganga in the districts of Patna, Bhojpur and Bhagalpur; and along the northern bank in Vaishali district, Methodology- This research team formulated the Protocol, duly approved by Govt. of Bihar, Govt. of U.P., and UNICEF, for detection of arsenic over large areas. This Protocol is specifically intended for use by all those involved with arsenic detection in hand pumps using field test kits. The methodology incorporated in the Protocol has the following five significant components- • All the public hand pumps of the study area were tested for Arsenic content through Field Test Kits by trained Staff. • Each public hand pump tested was marked, with a unique Identification Code at the time of testing. The 13-digit code was derived from the Census 2001. This information identified the State, District, block and village, and finally the serial number of the Hand pump. • Bihar Plains consist of sandy soils, where recent research has shown that presence of silica often masks the signal of arsenic from many chemicals11, thereby “creating a false optimum” of arsenic content lower than actually existing. Hence, 10% random verification of field test kit results was done through Atomic Absorption Spectroscopy. • All field test results above 40μg/l were retested using AAS / UV Spectrophotometer23. • Marking of hand pumps were done to inform the public of their status (safe/unsafe). The color codes applied were – Blue for FTK readings below 40 ppb.; yellow for FTK readings 40- 79 ppb.; and, Red for FTK readings of 80 ppb. and above. • There is an increasing need to map the level of arsenic concentration, trends of arsenic flow and temporal changes occurring in its concentration levels. Recording the locations of Arsenic-affected hand pumps, using Global Positioning System (GPS) units24, was done, followed by mapping of the arsenic occurrences.