Mousumi Chatterjee

A comparison of sediment quality guidelines for toxicity assessment in the Sunderban wetlands (Bay of Bengal, India).

The aim of this paper was to obtain the first screening ecotoxicological risk evaluation in the Sunderban wetlands, the largest prograding delta in the estuarine phase of the River Ganges. The characterization of exposure was conducted by means of an extensive survey of several persistent organic pollutants (PAHs, PCBs, DDTs, PBDEs, HCHs, HCB) measured in seven core sediments from the Sunderban wetlands, obtaining a dataset with more than 2200 analyses. The pollutant effects were assessed by the use of three different sediment quality guidelines (SQGs) previously developed in the literature to evaluate toxicity induced in sediment-dwelling organisms. The three different approaches chosen for risk assessment of the Sunderban were the consensus SQGs obtained by TEC (threshold effect concentration), PEC (probable effect concentration) and EEC (extreme effect concentration), the threshold/probable effect level (TEL/PEL) approach and, finally, the ERL-ERM guidelines, including the m-ERM-Q (mean ERM quotient). The evaluation of the toxicity induced by a mixture of the target pollutants indicated the importance of gamma-HCH contamination in the Sunderban sediments despite the very low concentrations measured in core sediments. A different sensitivity for toxicity assessment due to quality guidelines was obtained, as the consensus SQGs based on TEC were less conservative and protective than the TEL and ERL approaches, while the use of m-ERM-Q seems to be the most powerful tool to predict the toxicity related to a contaminant mixture.

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.

Distribution and Ecosystem Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Core Sediments of Sundarban Mangrove Wetland, India

The origin and distribution of 19 priority pollutant polycyclic aromatic hydrocarbons (PAHs) in core sediments (<63 μm) from the Sundarban mangrove wetland, northeastern part of Bay of Bengal, India, were investigated by gas-chromatography/mass spectrometry (GC/MS). Sedimentary organic carbon and textural properties were also analyzed in order to assess the role of geochemistry on PAH distribution. ∑19PAHs concentration in sediments showed wide variations from 9.4–4222.8 ng/g dry weight, with an overall increase of the high molecular PAHs in the deeper depth profiles. Fluoranthene, chrysene, and pyrene were the most abundant hydrocarbons in sediments and it can be explained by active inputs of soil materials due to frequent strong rainfalls in this tropical climatic zone. A rather exceptional prevalence of high molecular weight PAHs was substantiated: nearly 80% of ∑19PAHs include fluoranthene (18–20%), chrysene (14–16%), and pyrene (10–11%). Carcinogenic compounds were present in moderately high (DBA, BkF, BbF) or negligible and low concentrations (BaP, InP) in a majority of cases. The PAH diagnostic ratios indicated that the PAHs in sediment cores were of pyrolytic origin, and that atmospheric deposition and land runoff may serve as the important pathways for PAHs input to the sediments. The total PAH levels were expressed as the benzo (a) pyrene toxicity equivalents (TEQcarc) making this compound a potential marker for PAH pollution. The baseline data can be used for regular ecological monitoring, considering the industrial and agricultural growth around this important estuarine environment. The results indicated that the PAHs in sediments of Sundarban wetland resulted in low to moderate ecosystem risk.

Congener profiles of polychlorinated biphenyls in core sediments of Sunderban mangrove wetland (N.E. India) and their ecotoxicological significance

The paper presents the first comprehensive survey of congener profiles of polychlorinated biphenyls (PCBs) in core sediment samples (<63 μm particle size) covering seven sites in Sunderban mangrove Wetland, north-eastern part of the Bay of Bengal. Results pointed out a non-homogenous contamination of the wetland with Σ23PCB values ranging from 0.5 to 26.9 ng g-1 dry weight, reflecting very low to moderate contamination closely in conformity to other Asian coastal environment. The general decreasing order of the dominant congeners to the total load was: CB138 > 153 > 149 > 101, indicating the predominance of hexa-chlorinated congeners. The spatial distribution revealed significant differences in concentration related to local urbanization with industrial and land-based sources. No uniform temporal trend on PCB levels was recorded probably due to particular hydrological characteristics of the wetland and/or non-homogenous inputs from point sources. Strong positive correlations between the seven dominant congeners suggest their common sources and similar environmental behaviors. These results were also used for a risk assessment evaluation in the Sunderban wetland, showing that the present PCB levels were exceeding in few cases the lower limit of sediment quality guidelines of Environmental Protection Agency and Canadian Council of Ministers of the Environment.

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.

Persistent Organic Pollutants (POPs) in Sediments and Biota in Coastal Environments of India

Persistent organic pollutants (POPs) are semivolatile organic compounds of special concern because of their toxicity, persistence, long-range transport and bioaccumulation potential. They are present in the marine environment, notably in coastal areas affected by municipal sewage, agricultural and aquaculture effluents, industry and shipping traffic. The 7,555 km-length coastal region of India is the most vulnerable zone facing frequent geohazards, e.g. tsunami and flooding. It is contaminated from direct discharge of wastes from the densely populated coastal areas, runoff of fertilizers, dumping by vessels, oil spills, deforestation and ill-planned river basin developments. This chapter summarizes the knowlegde on residues of 5 classes of persistent organic pollutants (POPs) such as dichlorodiphenyltrichloroethane and its metabolites (DDTs), hexachlorocyclohexane and its isomers (HCHs), polycyclic aromatic hydrocarbon and its congeners (PAHs), polychorinated biphenyl and its congeners (PCBs) and polybrominated diphenyl ether and its congeners (PBDEs) in the sediments and in selective biota: bivalve mollusks, fishes and marine mammals. Their potential ecotoxicological impacts on biota have also been assessed based on the sediment quality guidelines (SQG) specified by USEPA (The incidence and severity of sediment contamination in surface waters of the United States, vol 1, National sediment quality survey. EPA 823-R-97-006, Washington, DC, 1997a: Environmental protection agency, National Sediment Quality Survey, App D, Washington DC, 1997b) and by Canadian Council of Ministers of the Environment (CCME, Canadian quality guidelines for the protection of aquatic life-summary tables. Available from. http://www.ccme.ca/assets/pdf/sed summary_table.pdf, 2002).