arsenic pollution in west bengal.pdf
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Arsenic Pollution in West Bengal D. Elangovan1 & M. L. Chalakh2 1.1 Historically arsenic is known as a poison. It does not often present in its elemental state but is more common in sulfides and sulfosalts such as Arsenopyrite, Orpiment, Realgar, Lollingite and Tennantite. Due to abundance of these arsenic bearing ores and the rarity of native arsenic, it is not an important ore itself. Arsenic is used in industry as a wood preservatives and in paints, dyes, metals, soaps, insecticides and semi-conductors. Apart from its natural occurrence it is also released into the environment through burning fossil fuels, paper production, cement manufacturing and mining activities. 1.2 Arsenic (AS) exists in several forms, which vary in toxicity and occurrence.
2.
Extent of problem in West Bengal
In West Bengal, during 1980s, some cases of arsenical dermatosis in the districts of North 24 Parganas, South 24 Parganas, Nadia, Murshidabad and Burdwan were reported. By the end of December 2001, this problem spreads from few villages to 2065 villages of 75 blocks in 8 districts. About 10 % of the total population of the State is exposed to the above risk. It can be observed from the map below that there is increase in number of incidences with the time. The details of the extent of the problem (as on December 2001)in West Bengal are given below.
The metallic form of arsenic (0 valency) is not absorbed by the stomach and intestines and does not exert adverse effects. On the other hand, a volatile compound such as AsH3 is toxic, but is not present in water or food. Moreover, the primary organic forms (arsenobetanine and arsenocholine) found in fish and shellfish seem to have little or no toxicity. Arsenobetanine quickly passes out of the body through urine without being metabolized to other compounds. Arsenite (+3) and arsenate (+5) are the most prevalent toxic forms of inorganic arsenic that are found in drinking water. Arsenite As(+3) in reduced state in inorganic is a toxic pollutant in natural environment and is more soluble and mobile than the oxidised state of inorganic arsenic, arsenate As(+5). 1.3 Intake of drinking water having arsenic concentration beyond the permissible limit of 0.05 mg/ lit has deleterious effects on human health viz., cardiovascular (heart failure) problem, gastrointestinal (burning lips, painful swallowing, thirst, nausea, and severe abdominal colic), hematological effects (anemia and leucopoenia), hepatic effects, renal effects, neurological effects (headache, lethargy, mental confusion, hallucination, seizures and coma), dermal effects (skin disorder, hyperkeratosis), carcinogenic effects ( lung Carcinoma cancer) etc. 1 2
General Manager, HO, NABARD Assistant Manager, West Bengal RO, NABARD
Identified upto May 1993. Further identified upto September 1995. Further identified upto December 1995. Further identified upto December 2000. Further identified upto December 2001.
According to the studies so far made, the cause of arsenic pollution of ground water in West Bengal has been attributed to the hydrolithological phenomena. Sr. District No. 1 2 3 4 5 6 7 8
Malda Murshidabad Nadia North 24 Parganas South 24 Parganas Howrah Hooghly Bardhaman Total
No. of blocks affected
No. of villages
Population at the village
7 18 17 19 9 2 1 2 75
229 354 541 472 409 4 18 38 2065
696822 1343866 1743889 1884676 964431 107951 37678 101171 6970484
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3.
Source of arsenic in groundwater
3.1 The source of arsenic in groundwater can be traced out by establishing the relations between the river system (drainage pattern), the area from where the rivers brought sediments i.s. parent materials. In this regard Geological Survey of India and Central Ground Water Board have done commendable job and come out with certain findings. 3.2 The problem of groundwater pollution by arsenic is found in the interfluvial region of the BhagirathiHugli and the Jalangi-Ichamati rivers lying mostly in the eastern part of the Bhagirathi-Hugli river of West Bengal. The arsenic contamination in ground water beyond permissible limit of 0.05mg/l has been found within the shallow aquifer (20-60m below ground level). Apart from this area, other areas where higher incidence of Arsenic has been reported are four blocks (adjacent to the river Ganga) in Malda district, Purbasthali block of Bardhaman district and Balagarh block of Hugli district. 3.3 During the phases of deltaic sedimentation in the southeastern part of West Bengal, rest of the Bengal shelf was under the influence of fresh water sedimentation. The system of rivers responsible for this fresh water sedimentation could be the precursor of the Ganga, which might have been flowing into the Bengal plains through the Garo-Rajmahal gap. A number of rivers like the Damodar, the Rupnarayan etc. flowing in the Bengal plains in a southeasterly direction for a considerable distance turn sharply to the south in the southern part of West Bengal. Thus the present drainage pattern responsible for subrecent to recent sedimentation in West Bengal might have been caused due to 1) a regional southeasterly slope of the basin, caused to some extent, by movements on the hinge-zone located at the edge of the shelf and 2) an increasing rate of southerly tilt of the West Bengal part of the basin due to relatively greater rate of subsidence of the southern part of the hinge through the Tertiary and recent times. 3.4 The river system and its Sedimentation The affected area is a part of the Ganga Brahmaputra delta having succession of Quaternary sediments of varying thickness. The deltaic region of Bengal formed the seaward continuation of the Bengal basin, which is bounded on three sides west, north and northeast by pre-cambrian crystalline rocks and on the eastern side by tertiary hill ranges of the Assam-Burma arc. This erosional history of the rivers and their numerous tributaries undergoing changes in the position of their
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sources several times during the epoch valley alluviation. These changes left irregularities on the alluvial plain, which controlled hydrographic pattern and created environments in which the sediments were deposited. With the beginning of the Himalayan orogeny crustal down wrapping along the northern margin of the peninsula and south of the newly formed mountain ranges gave rise to a basin in the nature of a foredeep where concomitantly with the formation of the mountain range extensive sedimentation took place. By middle Tertiary times the South Bengal basin was mainly getting sediments from Eastern part of the Peninsula comprising the Chotanagpur and the Assam Plateau. In he Tertiary period the sediments brought down from Chotanagpur plateau including Rajmahal hill area by Ajoy-Damodar system of rivers played the most important role in filling up the western margin of the Bengal basin. By the end of the Mid-Tertiary period the major uplifts of the Chotanagpur Plateau were over and the later movements were of much reduced magnitude. As a result, the rate of sedimentation during the Tertiary period was considerably reduced. The formation of Garo-Rajmahal gap in the Pleistocene completely changed the picture of sedimentation in the Bengal basin. A tremendous rate of growth started in south Bengal as a result sediments of northern rivers getting deposited there. The source of sediments deposited within last 2000 years could be from northern Himalayan provinces, metamorphic terrain of the Chotanagpur plateau the meta-sedimentary rocks of Eastern Himalaya. In eastern Himalayan foothills, the existences of Arsenopyrite Veins were reported at the altitude 1200 m above mean sea level. The Tista, Torsa and other tributaries of the Brahmaputra river have cut across the Darjeeling Coalfields and could carry pyrites, arsenopyrites etc., from the exposed coal seams occurring all along the eastern Himalayan foothills. The basaltic rocks of Rajmahal area lying in the northwestern part of the delta might have also supplied sedimentary detritus. Again, all the easterly flowing river cutting across Raniganj and other coalfields might also be responsible for bringing arsenic minerals from the mine workings. The heavy mineral assemblages from sub-surface sediments of Habra sediments of Habra block, North 24 Paraganas district in light grey micaceous fine to medium sand are kyanite-garnet-staurolite-biotitetourmaline-Chlorite-Hornblende-Epidote and those in
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Reddish brown sand are staurolite-garnet-sillimaniteopaque tourmaline-kyanite-biotite-chloride-epidote. In both the cases the source materials denote highly metamorphosed rocks. XRD analysis of sediments also indicates major quantities of quartz and feldspar with illite and chlorite clay minerals. Arsenic was observed to have been deposited as adsorbed primary metal on sand grains of biotite and quartz with a few scattered grains of arsenopyrite. Both in Murshidabad and North 24 Paraganas district, concentration of arsenic in acid leachate (pH 2.0) and alkali leachate (pH 12) was highest in the clay followed by sandy clay and lowest in sand. A striking difference between the sediment samples of 24 Paraganas and that of Murshidabad district is that in the former alkali leachates are appreciably higher than in the acid leachates while in the later the acid leachates are higher than the alkali leachates. It has been confirmed from EPMA and that there is LAMMA study the presence of arsenic in Pyrite (Fe S2) in some samples of North 24 Paraganas district. The decomposition of arsenic rich pyrite results in the formation of Fe 3+ ion which act as catalyst for the further decomposition of pyrite. 4.
Aquifer characteristics
Groundwater with higher concentration of arsenic generally occurs within 20-80m depth zone, commonly known as shallow aquifers. The deeper aquifers are by and large free from arsenic, except at a few places where no perceptible clay layer separates the lower one from the upper aquifer. The aquifer characteristics of both shallow, deep, unconfined and confined aquifers are given below. District
Malda
Depth Range Transmissivity Storativity(s) of Aquifer in (m2/day) (T) meters 20-95
758-2976
26-75 70-118
4512.10 7255.0
Within 50 5-150
790-4000 5200
1.1x10-2 to -4.38x10-4
10-50
1000-3000
1.1x10-3 to -5.6x10-4
70-195
4500-8000
7.3x10-1 to -3.5x10-4
24 South Parganas
236-276
1725
1.5x10-3
Howrah
150-230
446-1872
20-60
3000-5000
Murshidabad Nadia 24 North Parganas
Hughly
3.89x10 -3
101x10 -3 to 4.6x10-3
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Causes of High incidence of Arsenic in Groundwater
5.1 Some of the research workers believe that leaching of arsenic in groundwater seems to have been influenced by the number of interacting factors. 5.2 During the eighties there was a remarkable change in the minor irrigation sector due to rapid growth in Agro-commercialisation. Cultivation of Summer Paddy (Boro) expanded in the seven districts of South Bengal with an unpredictable rate each year. The Boro cropping is almost dependent on the tubewell irrigation. Immediate manifestation of that agro practice was lowering of ground water level at alarming rate. 5.3 As discussed in preceding paragraphs, the ground water occurring mainly within the shallow zone (20-60m bgl) is characterized by high arsenic (>0.5 to 1 or above mg/l) and the principal source of arsenic is the arsenic sulphides minerals deposited alongwith clay, peat, with iron in the reducing environment. The lowering of groundwater at rapid rate during summer season causes aeration of aquifer oxidized the arsenic sulphides, makes it water soluble. It percolates from the subsoil into water table during monsoon. 5.4 However, the cause of arsenic contamination in groundwater is still a debatable topic. Hence, it is necessary to study extensively the groundwater reservoir condition, mode of recharge-discharge relationship, groundwater movement characteristics in time and space and to determine dissolved oxygen and oxidation reduction potential in groundwater to appreciate the cause of such arsenic concentration in groundwater. 6.
Efforts made by State Govt.
6.1 The Govt. of West Bengal constituted a Steering Committee (First Committee) in May 1988 to examine and investigate the Arsenic contamination of ground water in the districts having reports of such contamination. The Committee submitted its final report in 1991 with the following major recommendations;
Only the deep 3rd aquifer should be tapped for drinking water supply.
The water in new tube wells should be tested for Arsenic prior to commissioning.
The yield from the 3rd aquifer should be so regulated as to avoid large-scale vertical leakage of Arsenic-rich water from the Upper Zone.
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The Committee also recommended further studies:
6.3 Progress made so far
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To detect the spread of Arsenic contamination to newer areas
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Finding out appropriate Arsenic removal technology
Several methods have been developed to remove arsenic from groundwater by the Public Health and Engineering Department (PHED), Govt of West Bengal, All India Institute of Hygiene and Public Health, Tropical School of Medicines (S.T. M.), Calcutta and School of Environmental Studies, Jadhavpur University which are indicated as follows.
6.2 Another Committee was constituted in April 1992 as a follow up of recommendations of the Steering Committee with the following terms of reference; The recommendations in the report submitted in October 1994 are as follows: a)
Safe depth of aquifer for tube wells in five arsenic affected districts (except Malda).
b)
Treatment for ground water / utilization of surface source for Malda District.
c)
Development of domestic filters to be fitted in hand pump with safe sludge disposal arrangements.
d)
Development of large scale Arsenic Removal Plants with sludge disposal arrangement.
e)
Change of cropping pattern requiring less ground water for irrigation.
f)
Epidemiological, clinical and therapeutic studies.
g)
Study the effect of chronic arsenic toxicity in animals.
h)
Study the impact of arsenic rich ground water in food chain.
i)
Setting up of District and State Level Laboratories.
j)
Research on exact cause contamination of ground water.
k)
Monitoring of ground water quality at least four times in a year.
l)
Provide adequate fund and other supports for investigation of renal effects.
of
arsenic
6.3 The State Government collected information from different countries who had encountered problem of arsenic pollution and the remedial measures taken by them. Interaction was made with experts from U.S.A, U.K., Germany, and China etc. to obtain the appropriate technology. The Government of India has also been requested to come in touch with these countries and have the necessary feed back from them.
6.3.1 Arsenic Removal Plant (ARP) fitted directly with Hand Pump This has been developed by PHED, GoWB by using adsorption technique. These ARP are functioning under continuous flow system and it is attached with the hand pump. Field studies conducted in arsenic affected villages indicated satisfactory performance of these units. About 1000 such units at the end of 31st March 2002 had been installed by the PHED and Zilla Parishad, benefiting around 2,50,000 population in the arsenic affected districts viz., Murshidabad (702 units), Nadia (32 units), North 24 parganas (175 units), South 4 parganas (25 units), Malda (62 units) etc. 6.3.2 Arsenic Removal Plant for piped water supply scheme. There are three such plants constructed by the GoWB out of the State Funded Action Plan as on 31st March 2002 at Sujapur, Kaliachak block of Malda district, Dhaititha, Basirhat block of North 24 Parganas district and Gobardanga of North 24 Parganas district benefiting around 0.70 lakh population. At the Sujapur ARP, the content of arsenic and iron was reduced from 0.2 mg/lit 0.25 mg/lit to 0.02 mg/ lit 0.03 mg/lit and 1.7 mg/lit - 2 mg/lit to 0.2 mg/lit 0.25 mg/lit respectively after installation of ARP.
Sujapur Arsenic removal Plant
6.3.3
Clariflocculator
Surface Water Projects
Various surface water projects aiming to give safe drinking water are under construction viz., Surface
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Water Project in South 24 Parganas covering 2.658 million population of 8 blocks, 2 municipalities and 18 non municipal towns., Rural Supply Water Project in North 24 Parganas covering population of 7.50 lakh population of 4 blocks, Surface Water Project in Malda covering 8.17 lakh population etc. 6.3.4
Domestic Filters
Various types domestic filters have been developed by the AIH &PH, PHED. These filters are fitted with sand as well as candle. School of Environmental Studies, Jadhavpur University have also developed such filters fitted with specially manufactured candles. These candles are fitted with tablets of chemicals, which are disposable. 6.3.5
AMAL Arsenic Removal Units
Bengal Engineering College has developed Arsenic Removal units which were constructed using the conventional domestic candle filters. About 7 AMAL Arsenic Removal units were installed by the college in 3 affected villages in the district of 24 Parganas(N). 6.3.6 As per the estimates, as on 31 December 2001, about 45 million population had been benefited from the different arsenic mitigation schemes. 7.0 Suggested Role of NABARD 7.1 R&D Support Although the arsenic problem is about two decades old and we are deeply concerned with the arsenic contamination of drinking water, surveys and detailed studies are not yet conducted on the amount of the arsenic in irrigation water and consequent entry of the element through food into the bodies of humans and animals (through vegetables, foodgrains etc.). This aspect can be studied under R&D grant assistance. Similarly, cause of arsenic contamination of ground water can also be considered under R&D grant assistance to the Universities, NGO which are already working in this field. This assistance can also be provided to popularize the low cost arsenic removal devices prepared by PHED, GoWB, Jadhavpur University, Bengal Engineering College.
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7.2 RIDF Assistance Under RIDF-X, a drinking water project involving a project cost of Rs. 180 crore was sanctioned in the Murshidabad, Nadia and North 24 Parganas districts. The project will be benefiting approximately 30 lakh population for the design year 2027. Similar kinds of projects can be sanctioned in other affected districts. 7.3 Encouraging Surface Water schemes and Rain water harvesting The surface water schemes viz., Lift Irrigation Schemes etc., for irrigation and drinking water on location specific basis may be encouraged in the affected districts. In addition to this, Rain Water can be harvested by construction of water harvesting tank (Farm Pond) in the command of the farmers and can be utilized in the water stress period. The availability of water in the farmers field during water stressed period will definitely help to avoid crop loss and further, these structures can be used to generate additional income by taking pisciculture. This can be achieved by proper implementation of the recently announced Rain Water Harvesting Scheme for SC and ST Farmers. While preparing the banking plan, due care has already been taken while allocating targets to these districts. For a wider benefit there is need to announce separate scheme or to extend the present scheme to other farmers also. There is a need to popularize such scheme to minimize the stress over the Ground Water and further contamination of arsenic in groundwater can be arrested. Reference: 1.
High incidence of Arsenic in Ground water in West Bengal report published by CGWB, GoI, Faridabad (July 1999)
2.
Various articles available on websites.
3.
Material available on the website of Govt. of West Bengal, Deptt. of Public Health and Engineering Department (PHED) .
4.
Website of School of Environmental Studies, Jadhavpur University
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