Hugli Research Articles

Shallow hydrostratigraphy in an arsenic affected region of Bengal Basin: Implication for targeting safe aquifers for drinking water supply

To delineate arsenic (As) safe aquifer(s) within shallow depth, the present study has investigated the shallow hydrostratigraphic framework over an area of 100km2 at Chakdaha Block of Nadia District, West Bengal. Drilling of 29 boreholes and subsequent hydrostratigraphic modeling has identified three types of aquifer within 50m below ground level (bgl). Aquifer-1 represents a thick paleochannel sequence, deposited parallel to the River Hooghly and Ichamati. Aquifer-2 is formed locally within the overbank deposits in the central floodplain area and its vertical extension is strictly limited to 25m bgl. Aquifer-3 is distributed underneath the overbank deposits and represents an interfluvial aquifer of the area. Aquifer-3 is of Pleistocene age (~70ka), while aquifer-1 and 2 represent the Holocene deposits (age <9.51ka), indicating that there was a major hiatus in the sediment deposition after depositing the aquifer-3. Over the area, aquifer-3 is markedly separated from the overlying Holocene deposits by successive upward sequences of brown and olive to pale blue impervious clay layers. The groundwater quality is very much similar in aquifer-1 and 2, where the concentration of As and Fe very commonly exceeds 10μg/L and 5mg/L, respectively. Based on similar sediment color, these two aquifers have jointly been designated as the gray sand aquifer (GSA), which constitutes 40% (1.84×109m3) of the total drilled volume (4.65×109m3). In aquifer-3, the concentration of As and Fe is very low, mostly <2μg/L and 1mg/L, respectively. This aquifer has been designated as the brown sand aquifer (BSA) according to color of the aquifer materials and represents 10% (4.8×108m3) of the total drilled volume. This study further documents that though the concentration of As is very low at BSA, the concentration of Mn often exceeds the drinking water guidelines.

Assessment of water quality index using cluster analysis and artificial neural network modeling: a case study of the Hooghly River basin, West Bengal, India

River Hooghly, considered as an important tributary of the River Ganga, has been affected by indiscriminate discharging of polluted and untreated sewage sludge and industrial waste into the waterways. The assessment of water quality for natural river waters was done using a water quality index (WQI), developed by DELPHI and the Council of Ministers of the Environment methods. These two methods reflect the quality of the water measured with respect to its pollution level. Multivariate statistical techniques, such as cluster analysis, were applied to the data-set on water quality of the Hooghly River (India) which was generated during the years 2002–2008 controlling at eight different sites for five parameters. The relationships among the stations are highlighted by cluster analysis to characterize the WQI. The study represents a computer-simulated artificial neural network model for the evaluation of the relationship between the different parameters of water bodies collected at different stations along Hooghly River responsible for water quality measurement. Finally, both the water quality methods (CCME and DELPHI) were statistically compared by the coefficient of determination (R2), root mean square error, and absolute average deviation based on the validation data-set.

Seasonal variations in species composition, abundance, biomass and production rate of tintinnids (Ciliata: Protozoa) along the Hooghly (Ganges) River Estuary, India: a multivariate approach

The study is the first documentation of seasonal variations in species composition, abundance and diversity of tintinnid (Ciliata: Protozoa), in relation to water quality parameters along the stretch of the Hooghly (Ganges) River Estuary (HRE), eastern coastal part of India. A total of 26 species (22 agglomerated and 4 non-agglomerated) belonging to 8 genera has been identified from 8 study sites where Tintinnopsis (17 species) represented the most dominant genera, contributing up to 65 % of total tintinnid community followed by Tintinnidium (2 species), Leprotintinnus (2 species) and Dadayiella, Favella, Metacylis, Eutintinnus and Helicostomella (each with solitary species). The maximum (1,666 ind. l(-1)) and minimum (62 ind. l(-1)) abundance of tintinnids was recorded during post-monsoon and monsoon, respectively. A distinct seasonal dynamics in terms of biomass (0.005-2.465 μg C l(-1)) and daily production rate (0.04-3.13 μg C l(-1) day(-1)) was also noticed, accounting highest value during pre-monsoon. Chlorophyll a and nitrate were found to be potential causative factors for the seasonal variations of tintinnids as revealed by a stepwise multiple regression model. The result of ANOVA showed a significant variation between species abundance and months (F = 2.36, P ≤ 0.05). k-dominance curves were plotted to determine the comparison of tintinnid dominance between the investigated stations. Based on a principal component analysis (PCA), three main groups were delineated with tintinnid ciliates and environmental parameters. The changes in lorica morphology in terms of temperature and salinity, recorded for three dominant species, provided information on the ecological characteristics of the species assemblage in this estuarine system.

Dactylogyrids (Monogenoidea: Polyonchoinea) parasitising the gills of snappers (Perciformes: Lutjanidae): Species of Euryhaliotrema Kritsky &amp; Boeger, 2002 from the golden snapper Lutjanus johnii (Bloch) off northern Australia, with a redescription of Euryhaliotrema johni (Tripathi, 1959) and descriptions of two new species

Three species of Euryhaliotrema Kritsky & Boeger, 2002 (Monogenoidea: Dactylogyridae) were collected from the gills of four golden snapper Lutjanus johnii (Bloch) (Lutjanidae) from the marine and brackish waters off Darwin, Northern Territory, Australia. Type-specimens of Ancyrocephalus johni Tripathi, 1959 apparently have not survived and the possibility existed that the species was based on specimens representing more than one species. Euryhaliotrema johni (Tripathi, 1959) (sensu Young, 1968) was redescribed and determined to most likely represent A. johni, originally described from the River Hooghly, Diamond Harbour, India. Two new species were described. Euryhaliotrema longibaculoides n. sp. was most similar to Euryhaliotrema longibaculum (Zhukov, 1976) Kritsky & Boeger, 2002 from Lutjanus spp. from the western Atlantic Ocean. It differed from E. longibaculum by having a male copulatory organ (MCO) with an elongate comparatively delicate shaft and a bulbous base (MCO U- or J-shaped with funnel-shaped base in E. longibaculum). Based on the comparative morphology of the haptoral sclerites, Euryhaliotrema lisae n. sp. was most similar to Euryhaliotrema cryptophallus Kritsky & Yang, 2012 from the gills of the mangrove red snapper Lutjanus argentimaculatus (Forsskål) from the South China Sea. Euryhaliotrema lisae differed from E. cryptophallus by having a copulatory complex with an obvious weakly sclerotised J-shaped MCO (MCO cryptic, delicate, and with a shaft comprising about one counterclockwise ring in E. cryptophallus).

Influence of the River Ganga on the Urban Process in Kolkata Metropolitan Area

From the dawn of human civilization, rivers have been playing a significant role for the development of human settlement worldwide. The Kolkata Metropolitan Area (KMA) is no exception to this. It is located on the bank of river Hugli, the distributory of river Ganga at its lower course in India. In the medieval and early modern period it was the most important riverine trade route in eastern India when market based economy was started to develop. In the later phase Kolkata (erstwhile Calcutta) port and adjoining town was established. Afterwards, this port town expanded rapidly to become the metropolitan city of Kolkata, which was the national capital of British India till 1911and became the main center of economic, cultural and political activities in the country. Following the partition and independence of India, a phenomenal change in the population distribution took place as a result of huge refugee influx from erstwhile East Pakistan, now Bangladesh. At that time river Hugli acted as a major barrier of migration flow between the eastern and western districts of KMA. Even today, effects of such immigration are reflected through population pressure differential on both the banks within KMA. Apart from that, the land use and morphology of this metropolis is also profoundly affected by the existence of river Hugli. The current study is an attempt to explore these all round influences of river Hugli on KMA.

Seasonal Dynamics of Surface Micro Phytoplankton Assemblages in an Understudied Tropical Estuarine Station Along the Bhagirathi–Hooghly Estuary, India

Near shore surface water (0.5 m) of an estuarine station along eastern Indian coast was studied for the first time to understand the seasonal composition, distribution and assemblage patterns of micro phytoplankton in relation to different environmental variables. Regular samplings at bi weekly intervals for micro phytoplankton and water samples were carried out for a period of 2 years (July 2007–June 2009). Implementation of multivariate procedures like principal component analysis and multi dimensional scaling allowed us to enumerate the regulatory role of environmental variables in seasonal micro phytoplankton succession. The habitat water was slightly alkaline with variations in salinity from 4 to 17 psu. 25 micro phytoplankton taxa were recorded during the study period, with green algal dominance in summer and diatom dominance in winter. Seasonal changes in abundance and the diversity of micro phytoplankton population differed significantly, showing maximum diversity in autumn and minimum in winter. Species richness ranged from 7 to 16 with low inter annual variations. The study area represented a habitat where nutrients were optimally present with low micro phytoplankton cell counts. Distinct seasonal succession pattern was prevalent in the study area where nutrient concentrations, temperature and salinity played deterministic roles in regulating seasonal micro phytoplankton assemblages.

High genotoxicity of shipyard contaminants on Allium cepa and calf thymus DNA

Water pollution is a major environmental problem worldwide. In particular, shipyards are contaminating waters with iron, lead and copper filings, paints, petrochemical products and solvents. There are only a few reports on the genotoxicity of shipyard contaminants. Here, we study genotoxic effects of surface water from five sites of Hooghly River in West Bengal, India, along the banks of which many shipbuilding and scrap industries are located. Genotoxicity was measured by the detection of micronuclei in Allium cepa and other chromosomal aberrations, as well as damage to genomic DNA of calf thymus. Results show that A. cepa roots treated with contaminated water induced morphological distortions, formation of micronuclei and various types of chromosomal aberrations. The mitotic index was lower than 50 % in the treated samples. The breakage of calf thymus DNA was time-dependent with acute damage of 100 % for overnight incubation as evidenced by agarose gel electrophoresis. We conclude that the workers of local shipbuilding and scrap industries, the residents of nearby areas and the aquatic biodiversity are vulnerable to contaminated waters.

Influence of hydrologic and anthropogenic factors on the abundance variability of enteropathogens in the Ganges estuary, a cholera endemic region

This study deals with the influence of water physico-chemical properties, tides, rainfall and fecal pollution on the abundance of enteropathogens in a main distributary of the Ganges, in the endemic cholera belt of West Bengal. Between January and June 2011, water and sediments were sampled from two sites of the Hooghly River by Kolkata and Diamond Harbour. Counts of cultivable Vibrio (CVC, from~102 to~105CFU/L) and total bacteria (TBC, from~105 to~109CFU/L) increased with water temperature (17°C to 37°C). A combination of variations in tidal height, salinity and turbidity had a distinct influence on CVC, TBC and coliform counts. At Diamond Harbour, a salinity increase from 0.6 to 7.9 was accompanied by a 1000-fold amplification of initial CVC~102CFU/L, whereas higher prevalence of coliforms in Kolkata was related to greater disposal of untreated sewage into the river. Turbidity-dependent variation of CVC was noteworthy, particularly at Diamond Harbour, where CVC in intertidal surface sediments showed an analogous trend as in surface waters, suggesting bentho-pelagic coupling of Vibrio dynamics. Besides the influence of salinity variation with tidal cycles, sediment re-suspension from tidal flats can play a role on Vibrio abundance in aquatic ecosystems.

Cunning Strategy for Upstream Water Piracy and Remedial Measures

Abstract India has been pirating 60% of the Bangladesh Gangetic ecosystem's water since 1975 after construction of a feeder canal by the Farakka Barrage in the name of maintaining the navigability of the Calcutta Port located at the mouth of the Hooghly River. As a consequence, massive ecocide has unfolded in Bangladesh. India's forced piracy and Bangladesh's compelled consent to piracy, for a meager discharge, have continued for the past forty years. This study focuses on Calcutta Port's navigability source, navigability loss and past maintenance, India's water crisis, and India's use of the looted water resources. Sources of information included electronic and print media, site visitations, expert interviews, fieldwork, travel accounts, research institutions, and government offices. The study finds Calcutta Port's brisk use during the British period, Calcutta Port's Ganges discharge-independent establishment, India's development of other ports in post-independent India, the storage of the Hooghly's wate...

Reconstructing the sedimentation history of the Bengal Delta Plain by means of geochemical and stable isotopic data

The purpose of this study is to examine the sedimentation history of the central floodplain area of the Bengal Delta Plain in West Bengal, India. Sediments from two boreholes were analyzed regarding lithology, geochemistry and the stable isotopic composition of embedded organic matter. Different lithofacies were distinguished that reflect frequent changes in the prevailing sedimentary depositional environment of the study area. The lowest facies comprises poorly sorted fluvial sediments composed of fine gravel to clay pointing at high transport energy and intense relocation processes. This facies is considered to belong to an early Holocene lowstand systems tract that followed the last glacial maximum. Fine to medium sands above it mark a gradual change towards a transgressive systems tract. Upwards increasing proportions of silt and the stable isotopic composition of embedded organic matter both indicate a gradual change from fluvial channel infill sediments towards more estuarine and marine influenced deposits. Youngest sediments are composed of clayey and silty overbank deposits of the Hooghly River that have formed a vast low-relief delta-floodplain. Close to the surface, small concretions of secondary Mn-oxides and Fe-(oxyhydr)oxides occur and mark the fluctuation range of the unsaturated zone. These concretions are accompanied by relatively high contents of trace elements such as Zn, Ni, Cu, and As. To sum up, the outcomes of this study provide new insights into the complex sedimentation history of the barely investigated central floodplain area of West Bengal.

Bioluminescent bioreporter for assessment of arsenic contamination in water samples of India

In the present study the most efficient R-factor controlling the ars operon was selected after screening of 39 Escherichia coli isolates by minimum inhibitory concentration test (MIC) studies from water samples of different geographical locations of India. Among all, strain isolated from Hooghly River (West Bengal) was found to have maximum tolerance towards arsenic and was further used for the development of bioreporter bacteria. Cloning of the ars regulatory element along with operator-promotor and luxCDABE from Photobacteria into expression vector has been accomplished by following recombinant DNA protocols. The bioreporter sensor system developed in this study can measure the estimated range of 0.74-60 mu g of As/L and is both specific and selective for sensing bioavailable As. The constructed bacterial biosensor was further used for the determination of arsenic ion concentration in different environmental samples of India.

Levels and chemical speciation of arsenic in representative biota and sediments of a tropical mangrove wetland, India

The general concern for arsenic in the marine environment is associated with its wide distribution and potential toxicity. In the present work, concentrations and chemical speciation of arsenic were characterized in sediments and representative biota from the Indian Sundarban, the largest continuous mangrove tract formed at the mouth of the Hugli (Ganges) River estuary, northeastern part of the Bay of Bengal. Analyzed organisms included both shellfish (Macoma birmanica, Sanguinolaria acuminata and Meretrix meretrix) and finfish (Liza parsia, Liza tade, Harpodon nehereus and Eleutheronema tetradactylum). Arsenic concentrations in sediments did not exceed 4 μg g(-1) dry weight with the contribution of inorganic molecules (arsenate and arsenite) ranging from 61.7 to 81.3%. Total As (TAs) concentrations varied from less than 2 to 16 μg g(-1) in tissues of bivalves; the more elevated As accumulation was observed in gills and the mantle probably due to ion exchange properties of the mucous layer covering these organs, whereas adductor muscle and the podium showed limited values. Distribution of various arsenic compounds followed a quite similar trend in bivalve tissues; arsenobetaine (AsB) was the most dominant form followed by compounds such as dimethylarsinate (DMA), trimethyl arsine-oxide (TMAO), tetramethyl arsonium (TETRA) and arsenocholine (AsC), while inorganic arsenic (IAs) represented a minor constituent (0.2 to 6.9%). Among the fish, detritivorous/herbivorous species (L. parsia and L. tade) exhibited TAs concentrations of 10.8 and 9.71 μg g(-1) dry wt with a prevalence of AsB (52-67%) and TETRA (26-35%); higher concentrations of TAs were measured in the two carnivorous species (20.62 and 19.67 μg g(-1) dry wt, in H. nehereus and E. tetradactylum respectively) mostly as AsB (63.3-72.3%) and AsC (17.5-28.6%). The obtained results can be considered as baseline levels for arsenic in the investigated area, confirming the predominance of organoarsenicals in marine organisms compared to more toxic inorganic compounds. Considering the ecological importance of this ecosystem and the increasing anthropogenic impact, the distribution of arsenic through the food chain should be continuously monitored, using organisms of different feeding guilds as indicators.

Influence of Physicochemical Parameters on the Abundance of Coliform Bacteria in an Industrial Site of the Hooghly River, India

Industrial effluents from jute, paper, pulp mills and sewage from households are regularly discharged into the Hooghly River. It generates a potential risk for both humans and animals of the area concerned. In the present study, water quality of the Hooghly River passing by the site of a growing township (Naihati, North 24 Parganas, West Bengal, India) was assessed throughout the year 2010 on the basis of the data collected on the physicochemical and microbiological parameters. The water samples collected on each month revealed the presence of higher amount of coliform bacteria, Streptococcus sp. and Escherichia coli, than the standard limit. Different physicochemical parameters like chemical oxygen demand, biological oxygen demand, dissolved oxygen (DO), total suspended solids, total dissolved solids (TDS), total hardness, alkalinity, chlorinity, nitrate and nitrite of the water at the sampling sites were found to be considerably higher than the levels standardized by WHO (2006). It was found that the relative abundance of Streptococcus and E. coli was influenced by two independent variables (water quality parameters), namely, DO and TDS. The abundance of coliform bacteria in the water sample warrants the adoption of proper measures to reduce the pollution level at the point source on way of scientific disposal of industrial effluents.

Short- and long-term temporal variations in salinity and the oxygen, carbon and hydrogen isotopic compositions of the Hooghly Estuary water, India

The Hooghly River estuary provides a unique experimental site to understand the effect of monsoonal river discharge on freshwater and seawater mixing. Water samples collected bi-weekly for a duration of 17months were analyzed for salinity, δ18O, δ13CDIC, as well as δD to investigate the differential mixing of freshwater and seawater. The differences in salinity and δ18O of samples collected during low and high tides on the same day are strongly correlated suggesting a well mixed water column at our sampling site. Low salinity and depleted δ18O during monsoon is consistent with increased river discharge as well as high rainfall. We identified different slopes in a δ18O versus salinity plot for the estuary water samples collected during monsoon and non-monsoon seasons. This is driven by composition of the freshwater source which is dominated by rainwater during monsoon and rivers during non-monsoon months. Selected δD analyses of samples indicate that groundwater contributes significantly to the Hooghly Estuary during low rainfall times of the year. δ13CDIC measured in the water recorded low values towards the end of monsoon indicating low productivity (i.e. increased organic respiration) while progressively increasing δ13CDIC values from October till January as well as during some of the pre-monsoon months can be explained by increasing productivity. Very low δ13CDIC (~−20‰) suggests involvement of carbon derived from anaerobic oxidation of organics and/or methane with potential contribution from increased anthropogenic water supply. An estimate of seawater incursion into the Hooghly Estuary at different times of the year is obtained by using salinity data in a two-component mixing model. Presence of seawater was found maximum (31–37%) during February till July and lowest (less than or equal to 6%) from September till November. We notice a temporal offset between Ganges River discharge farther upstream at Farakka and salinity variation at the Hooghly Estuary. We believe that this time lag is a result of the physical distance between Farakka and Kakdweep (our sampling location) and put constraints on the travel time of river water during early monsoon.

Environmental hazards and community responses in Sagar Island, India

Sagar Island is situated at the estuary of the river Hugli and prone to several environmental hazards. Erosion, cyclones, tidal surges and floods are the four major environmental hazards occurring continuously in this Island. In this paper an attempt has been made to analyse the perception of several occupational groups of the Island about the adverse effects of the four major environmental hazards. The study has examined in detail how different occupational groups perceive the environmental hazards from their respective occupational standpoints. An amalgamation of the diverse perceptions of various occupational groups and their active involvement in various stages of hazards management is suggested to protect the Island from devastating effects of environmental hazards.

A megacity in a changing climate: the case of Kolkata

Projections by the Intergovernmental Panel on Climate Change suggest that there will be an increase in the frequency and intensity of climate extremes in the 21st century. Kolkata, a megacity in India, has been singled out as one of the urban centers vulnerable to climate risks. Modest flooding during monsoons at high tide in the Hooghly River is a recurring hazard in Kolkata. More intense rainfall, riverine flooding, sea level rise, and coastal storm surges in a changing climate can lead to widespread and severe flooding and bring the city to a standstill for several days. Using rainfall data, high and low emissions scenarios, and sea level rise of 27 cm by 2050, this paper assesses the vulnerability of Kolkata to increasingly intense precipitation events for return periods of 30, 50, and 100 years. It makes location-specific inundation depth and duration projections using hydrological, hydraulic, and urban storm models with geographic overlays. High resolution spatial analysis provides a roadmap for designing adaptation schemes to minimize the impacts of climate change. The modeling results show that de-silting of the main sewers would reduce vulnerable population estimates by at least 5 %.

Mercury Concentration in Sediment Cores from Sundarban Mangrove Wetland, India

The work presents an extended database (n = 123) of total mercury (THg) in fine-grained sediment fraction (<63 μm) of core samples in 10 sampling stations of the Sundarban mangrove wetland, India, formed at the estuarine realm of the Hugli (Ganga) River. Results revealed a wide range of spatial, seasonal, and intertidal flat variations of THg (7.3 to 93.3 ng/g) with a definite enhancement level at the lower stretch of the estuary, which has extreme mangrove vegetation. An overall enrichment of THg in surface/subsurface layers of the core is tentatively explained by remobilization and resuspension of the metal from deeper sediments (36–40 cm). A strong positive correlation was observed between the Hg and clay fraction content of the sediments, while correlations of Hg with organic carbon was poor. Based on the index of geoaccumulation (Igeo), enrichment factor (EF), and anthropogenic factor (AF) values, it is suggested that the sediments of Sundarban were found to be less polluted with respect to total mercury. The data reported are a useful baseline for THg in Sundarban and would be of importance in future sediment quality studies.

Cross-Dressing the Rose: Sly Allegory in Sea of Poppies

Names continually slip their moorings in the watery world of Sea of Poppies. Deeti, the first of the main characters we meet, experiences rebirth on the Ganges and takes as an alias her unused given name, Aditi, eventually inscribed by a tone-deaf colonial official as Aditty. Born on the River Hooghly, Paulette is dubbed Putli (“doll”) by her Bengali ayah, Puggli by the English family that takes her in as an orphaned adolescent, then Pugli (“mad”) by herself as she ventures seaward in disguise. Zachary Reid departs Baltimore as son of a freedwoman and as a “black” carpenter on the schooner Ibis and arrives in Calcutta as the second mate; passing as white, he is designated Malum Zikri by the “lascar” crew. Time and again Amitav Ghosh’s story probes the power and the limits of naming, drawing unstable borders for race, caste, language, humans, plants, and animals while acknowledging both the hope and the violence of alienation. Ostensibly a historical novel set on the eve of Britain’s opium wars with China, Sea of Poppies works to expose the ruthless, inexorable destruction wrought by the opium trade in India, the degradations of “coolie” indentured servitude and its links to American slavery, and, by implication, the ironic relationship of this history to the political discourse of “freedom” and “free trade” today. My focus here will be the relation of all this to the novel’s postcolonial allegorical method, which I take to have a double valence. While the characters’ movements allegorize the relation between power and the disposition of goods/bodies, thus tracking the pattern of history and the vantage from which it will be written, the lability of names invokes the very premise of allegory itself, and signals the impossibility of power to totalize. Repeating differently, names slip the hold of official identification, setting up a pattern that comments upon the differential structure of allegory as famously described by Paul de Man: “it remains necessary, if there is to be allegory, that the allegorical sign refer to another sign that precedes it. The meaning constituted by the allegorical sign can then consist only in the repetition . . . of a previous sign with which it can never coincide.” Postcolonial authors

Historic Buildings at Chitpur in Kolkata: Problems and Prospects Through Urban Conservation and Planning

Kolkata (historically Calcutta) is a linear city that has grown along the eastern bank of the river Hugli (also spelled Hooghly, and traditionally called the Ganges, in the West Bengal State of India. It served as the capital city of British India from 1773–1910. The British developed colonial architecture mostly in the central business district and the residential area designated for them. In the Chitpur area of north Kolkata, the Indians constructed buildings following European styles, but modifying parts according to their own social customs, individual choices and dictation – thus introducing a new style which was termed “Bengal Baroque” by some and generally called the “indigenous style”. Other old buildings also follow certain architectural typology and bear the history of eminent personalities of the society, thus constituting an overall cultural setting. However, many old buildings are in bad physical condition and have legal litigation. Meanwhile, tremendous real estate development and uncontrolled traffic circulation within this historic district are destroying the buildings, the historic cultural patina and the essence of the place. An urban design and planning solution is to be sought which would encompass the conservation of historic and old buildings and elements of the area as well as control over development for cultural compatibility and environmental sustainability.

Geochemical fractionation of trace elements in sediments of Hugli River (Ganges) and Sundarban wetland (West Bengal, India)

A sequential extraction procedure was carried out to determinate the concentrations of 11 elements (Al, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in different geochemical phases of sediments collected along the Hugli (Ganges) River Estuary and in the Sundarban mangrove wetland, eastern coastal part of India. The chemical speciation of elements was determined using the three-step sequential extraction procedure described by the European Community Bureau of Reference. Total metal concentration was determined using a microwave-assisted acid digestion procedure. Metal concentrations were near the background level except for As for which a moderate pollution can be hypothesized. The mobility order of the metals was: Cd > Mn > Cu > Zn > As > Co > Pb > Ni > Fe > Cr > Al. The highest percentage of Cd (>60%) was found in the most labile phase. Residual fraction was prevailing for Fe, Cr and Al, while Pb was mainly associated with the reducible fraction. Data were compared with Sediment Quality Guidelines to estimate the relationship between element concentrations and adverse biological effects on benthic community, finding the possibility of some toxic effects due to the presence of As in the entire studied area and Cd, only in Calcutta.