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HEAVY METAL POLLUTION IN THE LOWER GANGETIC MANGROVE ECOSYSTEM

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The Gangetic delta, sustaining the Sundarbans mangrove forest at the apex of the Bay of Bengal is recognized as one of the most diversified and productive ecosystems in the Indian subcontinent. The deltaic lobe is unique for its wilderness, mangrove
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    (   C   )    E  m  e  r  a   l  d   G  r  o  u  p    P  u   b   l   i  s   h   i  n  g  CHAPTER 5HEAVY METAL POLLUTION INTHE LOWER GANGETICMANGROVE ECOSYSTEM Abhijit Mitra, Sufia Zaman andSubhra Bikash Bhattacharyya ABSTRACT The Gangetic delta, sustaining the Sundarbans mangrove forest at theapex of the Bay of Bengal is recognized as one of the most diversified and productive ecosystems in the Indian subcontinent. The deltaic lobe isunique for its wilderness, mangrove gene pool and tiger habitat.However, due to intense industrial activities in the upstream zone, and several anthropogenic factors, the aquatic phase in the western part of the deltaic complex is exposed to pollution from domestic sewage and industrial effluents leading to serious impacts on biota. The presence of Haldia port-cum-industrial complex in the upstream region of the lowerGangetic delta (adjacent to western sector of Indian Sundarbans) hasaccelerated the pollution problem to a much greater dimension. Theorganic and inorganic wastes released from industries and urban unitscontain substantial concentrations of heavy metals. The present articleaims to highlight the level of selective heavy metals (zinc, copper, and lead) in the water and muscle of a commercially important shellfish Water Insecurity: A Social DilemmaCommunity, Environment and Disaster Risk Management, Volume 13, 97  113Copyright r 2013 by Emerald Group Publishing LimitedAll rights of reproduction in any form reservedISSN: 2040-7262/doi:10.1108/S2040-7262(2013)0000013011 97    (   C   )    E  m  e  r  a   l  d   G  r  o  u  p    P  u   b   l   i  s   h   i  n  g  species (Penaeus monodon, commonly known as tiger prawn) collected  from two sectors (western and central) in the Indian Sundarbans. Heavymetals are accumulated in the prawn muscle in the following order   zinc > copper > lead     which is similar to the order in the ambient estuar-ine water. Significant spatial variations of heavy metal concentrations inestuarine water and prawn muscle were observed between the selected sectors, which reflect the adverse impact of intense industrialization,unplanned tourism, and rapid urbanization on the mangrove ecosystemand its biotic community, particularly in the western Indian Sundarbans. Keywords:  Heavy metal; tiger prawn; Indian Sundarbans;spatial variation; temporal variation HEAVY METAL POLLUTION IN MARINE ANDESTUARINE ENVIRONMENT: AN OVERVIEW Estuaries are important conveyor belts for transport of all categories of wastes from continents into the oceans, which has made the aquatic systemhighly insecure from the ecological point of view. The sea and more particu-larly the aquatic system (e.g., estuaries) are the ultimate repository of alltypes of industrial, agricultural, municipal, domestic, and nuclear wastes.Today heavy metal pollution is a vital issue in the domain of ecological inse-curity of water. The coastal zone receives a large amount of metal pollutantsfrom agricultural and industrial activity (Usero, Morillo, & Gracia, 2005).The highly dynamic nature of the marine and estuarine system allows forvery rapid assimilation of these materials by processes such as dilution, dis-persal, oxidation, degradation, or sequestration into sediments. However,the capacity for such assimilation is limited. Understanding the process of “absorption” by the oceans and estuaries and thereby determining their“assimilative capacities” has been the main challenge of research during thelast few decades. There is little doubt that significant successes have beenachieved in reducing the contamination of natural waters. Pollution byheavy metals is still a serious problem due to their toxicity and ability toaccumulate in the biota (Islam & Tanaka, 2004). There is a general concernabout the impact of metals in the aquatic environment (Grosell & Brix,2005). The contamination of the aquatic environment, however, has beenoccurring for centuries, but its extent has increased markedly in the last50 years due to technological developments and increased consumer use of  98 ABHIJIT MITRA ET AL.    (   C   )    E  m  e  r  a   l  d   G  r  o  u  p    P  u   b   l   i  s   h   i  n  g  materials containing these metals. Metals generally enter the aquaticenvironment through atmospheric deposition, erosion of geological matrixor due to anthropogenic activities caused by industrial effluents, domesticsewage, nuclear testing, and mining wastes (Reddy et al., 2007). From anenvironmental point of view, coastal zones can be considered as thegeographic space of interaction between terrestrial and marine ecosystemsthat is of great importance for the survival of a large variety of plants,animals, and marine species (Castro, Aguilera, Martinez, & Carrique,1999). Adverse anthropogenic effects on the coastal environment includeeutrophication, heavy metals, organic and microbial pollution, and oil spills(Boudouresque & Verlaque, 2002). The discharge of these wastes withoutadequate treatment often contaminate the estuarine water with heavymetals, many of which bioaccumulate in the tissues of resident organismslike fishes, oysters, crabs, shrimps, seaweeds, etc. In many parts of theworld, especially in coastal areas and on smaller islands, shellfish is a majorpart of food, which supplies all essential elements required for life processesin a balanced manner (Iyengar, 1991). In developing countries like India,the demand for protein is accelerating at a rapid rate. The annual per capitafish consumption in India is only 4 kg against the recommended 31 kg bythe Nutritional Advisory Committee on human nutrition (Santhanam,Ramanathan, & Jegatheesan, 1990). Aquaculture has become a peak indus-try in the present millennium, which involves seafood farming with shrimp,cuttlefish, squid, lobster, and such culinary delights are actually “cultivated”in water tanks under scientifically controlled conditions (Rajkhowa, 2005).Hence, estimation of heavy metal accumulation is of utmost importance inthis sector of biotic community. The standards for metal contaminants incrustacean tissue (under which tiger prawn comes) have been given byFranklin (1987) as 120 mg/kg, 400 mg/kg, and 4 mg/kg dry weight, respec-tively, for copper, zinc, and lead.Increased circulation of hazardous heavy metals in soil, water, and airhas raised considerable concern for environmental protection and humanhealth. The lower Gangetic delta is no exception to this usual trend. Therapid industrialization and urbanization of Kolkata, Howrah, and thenewly emerging Haldia complex in the maritime state of West Bengal hascaused considerable ecological imbalance in the adjacent coastal zone andmore particularly in Sundarban mangrove ecosystem (Mitra, 1998; Mitra & Choudhury, 1992). The Hooghly estuary    an extension of Ganga  Bhagirathi River system, situated on the western sector of the Gangeticdelta    receives drainage from these adjacent cities, which have sewage out-lets into the estuarine system of Indian Sundarbans. The chain of factories 99 Heavy Metal Pollution in the Lower Gangetic Mangrove Ecosystem    (   C   )    E  m  e  r  a   l  d   G  r  o  u  p    P  u   b   l   i  s   h   i  n  g  and industries situated on the western bank of the Hooghly estuary isa major cause of the gradual transformation of this beautiful ecotoneinto stinking cesspools of the megapolis. The lower part of the estuary hasmultifarious industries such as paper, textiles, chemicals, pharmaceuticals,plastic, shellac, food, leather, jute, tires, and cycle rims. These units arepoint sources of heavy metals in the estuarine water of mangrove-dominatedSundarbans in the lower Gangetic plain.Heavy metals such as copper, zinc, and lead are normal constituents of marine and estuarine environments, but when additional quantities areintroduced through industrial waste or sewage, they enter the biogeochem-ical cycle and pose negative impact on the biotic community. Due to thetoxic nature of certain heavy metals, these chemical constituents interferewith the ecology of a particular environment and on entering into the foodchain they cause potential health hazards, mainly to human beings. Reportson metal concentration in shrimps and crabs under natural conditions forcoastal waters of India are limited (Matkar, Ganpathy, & Pillai, 1981;Qasim et al., 1988; Zingde, Singbal, Moraes, & Reddy, 1976). Hence, it is important to investigate the levels of heavy metals in these organisms toassess whether the concentration is within the permissible level and will notpose any hazard to the consumers (Krishnamurti & Nair, 1999). It wasreported by several workers that the discharge of heavy metals into the seathrough rivers and streams results in the accumulation of pollutants in themarine environment especially within shrimps (Yusof, Mitra, Rahama, &Wood, 1994). Thus shellfish and shellfish products can be used for monitor-ing potential risk to humans because these are directly consumed by a largepopulation (Subramanian & Sukumar, 1998). Bioaccumulation patterns of metals in shellfish muscle can be utilized as effective indicators of environ-mental metal contamination (Atchinson, Murphy, Bishop, McIntosh, &Mayes, 1977; Larsson, Haux, & Sjobeck, 1985). However, different opinions also exist in context to use of shellfish as potential indicators of conservativepollutants. According to many researchers, some shellfishes by virtue of their mobile nature are not fair indicators of aquatic contamination, buttheir regular consumption by human beings makes it absolutely necessaryto monitor their different organs, particularly the muscle. In this article wepresent the heavy metal concentrations in the muscle of a commerciallyimportant shellfish species found abundantly in the estuarine water of lowerGangetic region, namely  Penaeus monodon , commonly known as tigerprawn. It is one of the costliest shellfish species and is sold for $10  15 perkilogram in the Indian market. The shrimp is also exported to the UnitedStates, France, the United Kingdom, and several European countries. The 100 ABHIJIT MITRA ET AL.    (   C   )    E  m  e  r  a   l  d   G  r  o  u  p    P  u   b   l   i  s   h   i  n  g  present study is therefore important not only from the safety point of viewof human health, but also from the quality point of view as this species hashigh export value and is therefore linked with the economy of the nation. DESCRIPTION OF THE STUDY SITE The River Ganga emerges from the glacier at Gangotri, about 7,010 mabove mean sea level in the Himalayas and flows down to the Bay of Bengal covering a distance of 2,525 km. In this length, Ganga passes along29 class-I cities (population over 100,000), 23 class-II cities (populationbetween 50,000 and 100,000) and 48 towns having less than 50,000 people.Stakeholders of several tiers are associated with this mighty river. About50% of the Indian population lives on the Ganga basin. Of total irrigatedarea in the country, 43% also falls within the Ganga basin and there areabout 100 urban settlements with a total population of about 120 million onits banks. Two sampling sites were selected each in and around the westernand central sectors of Indian Sundarbans (Fig. 1). This delta complex is situ-ated at the confluence of the River Ganga and the Bay of Bengal. Becauseof the presence of a rich gene pool, the Sundarbans has been declared as theBiosphere Reserve. The Reserve has an area of 9,630 sq. km and housessome 102 islands. The western sector of the deltaic lobe receives thesnowmelt water of mighty Himalayan glaciers after being regulated throughseveral barrages on the way. The central sector, on the other hand, isfully deprived of such supply due to heavy siltation and clogging of theBidyadhari channel in the late 15th century (Chaudhuri & Choudhury,1994). The western sector also receives waste and effluents of complex nat-ure from multifarious industries concentrated mainly in the upstream zone(Fig. 2). In this background four sampling stations (two each in western andcentral sectors) were selected (Table 1) to present the picture of selectiveheavy metals over a decade (2001  2012) in the estuarine water and muscleof tiger prawn. AQUATIC HEALTH: A TIME SERIES ANALYSIS The distribution of dissolved heavy metals exhibits the order of zinc > cop-per > lead both in the western and central Indian Sundarbans. The increasein urbanization and industrialization leads to an increase of discharges and, 101 Heavy Metal Pollution in the Lower Gangetic Mangrove Ecosystem
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