SEGH Articles

# The Indian Sundarban Mangrove wetland: an ecological perspective

01 February 2012
Dr Sarkar has carried out research on the changes in the ecological and pollution status of the Indian Sundarban mangrove wetlands, as a result of intense anthropological pressures affecting the biotic and abiotic compartments of this fragile ecosystem.

Dr Santosh Sarkar is a professor at the Department of Marine Science, University of Calcutta in India. Over the past 30 years he has carried out research on the changes in the ecological and pollution status of the Sundarban mangrove wetland, as a result of intense anthropological pressures affecting the biotic and abiotic compartments of this fragile ecosystem.

The Indian Sundarban is located in North East India, in close proximity to Kolkatta. It is the largest delta in the estuarine phase of the river Ganges, and is situated in the low-lying, meso-macrotidal, humid and tropical belt at the estuarine phase of the Ganges River and Bay of Bengal. The Sundarban hosts the world's largest mangrove forest together with associated flora and fauna.

There have been remarkable ecological changes due to multiple human activities. such as; excavation of sand from the sand dunes, dredging and intensive boating, deforestation, collection of prawn seed, immersion of idols in the river etc., thus affecting sediment and water quality as well as biodiversity.

Dr Sarkar has quantified the adverse impacts due to collection of tiger prawn seeds for aquacultural farms and molluscan shells for poultry feed and edible lime. Indiscriminate exploitation of these resources leads to a heavy reduction of the species concerned and other associated marine communities. The impacts of biodiversity loss and their after-effects on the ecobalance of the coastal system have become a matter of great concern to ecologists to maintain security and sustainability.

Collection of  tiger prawn seed (Penaeus monodon) from Sundarban coastal regions

Dr Sarkar first worked on the occurrence, distribution and sources of several persistent organic pollutants (POPs) (PAHs, PCBs, DDTs, PBDEs, HCHs, HCB) measured in  sediments from the Sundarban wetlands, obtaining a dataset with more than 2000 analyses. The POPs belong to a group of pollutants that are semivolatile, toxic and  bioaccumulative in nature and resist photolytic, chemical and biological degradation. The concentration of four isomers of  HCH exhibit a heterogenic distribution. Among the isomers and metabolites of HCH, DDT and PCB, alpha-HCH, pp ′-DDT and PCB 101, PCB 118,  PCB 153 and PCB 138  were found to be dominant. High ratios of metabolites of DDT to ∑ DDTs reveal recent use of DDT in this coastal environment. PBDE, an important group of brominated flame retardants (BFR), showed moderate to low contamination closely in uniformity to other Asian aquatic environments. The PAH diagnostic ratios indicated that the PAHs in sediment were of pyrolytic origin, contaminated by local vehicle combustion, biomass burning and domestic an industrial coal combustion.

Dr Sarkar performed the first screening ecotoxicological risk evaluation of the persistent organic pollutants (POPs) in the Sundarban wetland. 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 Sundarban were: (1) the consensus SQGs obtained by TEC (threshold effect concentration); (2) PEC (probable effect concentration; and (3) 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 gama-HCH contamination in the Sundarban sediments despite the very low concentrations measured in 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.

Collaborative research work with Michael Watts of the British Geological Survey, provided initial findings for arsenic speciation in four soft-bottom benthic polychaetes (Perenereis cultifera, Ganganereis sootai, Lumbrinereis notocirrata and Dendronereis arborifera) along with host sediments from the Sundarban mangrove wetland.  Arsenic concentrations in polychaete body tissues varied greatly, suggesting species-specific characteristics and inherent peculiarities in arsenic metabolism. Arsenic was generally present in polychaetes as arsenate (AsV) or arsenite (AsIII) (30 to 53 % as inorganic As) and dimethylarsinic acid (DMAV; <1 to 25 %). Arsenobetaine (AB; <16%), and PO4-arsenoriboside (8 to 48%) were also detected as minor constituents, whilst monomethylarsonic acid (MAV) was not detected in any of the polychaetes. The highest total As (14.7 mg kg-1 dry wt) was observed in the polychaete D. arborifera collected from the vicinity of a sewage outfall in which the majority of As was present as an uncharacterized compound (10.3 mg kg-1 dry wt) eluted prior to AB. Host sediments ranged from 2.5 to 10.4 mg kg-1 total As. This work supports the importance of speciation analysis of As, because of the ubiquitous occurrence of this metalloid in the environment, and its variable toxicity depending on chemical form. Follow up work is being carried out on further samples collected with the support of Royal Society funding.  This will enable consideration of a range of polychaete species in terms of diverse habitat and food preferences to assess the arsenic uptake pathways and to determine the influence of ecological factors on total As concentrations and species proportion in this wetland ecosystem.

Gradually a full picture of the growing impact of human activity on the pristine environment of the Sundarban mangrove wetlands is being developed.  This is gradually being achieved through multiple international collaborations and will provide vital information for the planning and use of land and waterways in the wetlands.

Professor Santosh Sarkar, Department of Marine Science, University of Kolkatta, Indiasarkar.santosh@gmail.com

References

Biogeochemistry of mercury and methylmercury in sediment cores from Sundarban mangrove wetland, India - a UNESCO World Heritage Site - Mousumi Chatterjee, João Canário, Santosh Kumar Sarkar, Vasco Branco, Nallamuthu Godhantaraman, Bhaskar Deb Bhattacharya, Asokkumar Bhattacharya  - Environmental Monitoring and Assessment, Springer. DOI:10.1007/s10661-011-2336-8 2011. http://www.springerlink.com/content/v16047jhk2027416/

Quantification and source identification of polycyclic aromatic hydrocarbons in core sediments from Sundarban Mangrove Wetland, India  - C. Domínguez; S. K. Sarkar, A Bhattacharya, M Chatterjee, B D Bhattacharya, E Jover,  J Albaigés, J M Bayona, Md. A Alam and K K Satpathy. Archives of Environmental Contamination and Toxicology, Springer Publishers, 59(1): 49 - 61, 2010.           http://www.springerlink.com/content/l32803q28210256t/

Metal concentrations in water and sediments from tourist beaches of   Acapulco, Mexico  - M.P. Jonathan, P.D. Roy, N. Thangadurai, S. Srinivasalu, P.F. Rodríguez Espinosa, S.K.Sarkar, C. Lakshumanan, M. Navarrete-López and N.P. Muñoz-Sevilla - Marine Pollution Bulletin, Springer, 62, 845-850, 2011. http://www.sciencedirect.com/science/article/pii/S0025326X11001135

Baseline of organotin contamination in sediments of Sunderban mangrove wetland and adjacent coastal regions, India - P . Anderson, S K Sarkar, B D Bhattacharya, M Chatterjee, K K Satpathy, T Peshkur and B Antizar-Ladislao. - Ecotoxicology,Springer, 20 (8), 1975-1983, 2011. DOI 10.1007/s10646-011-0739-5. http://www.springerlink.com/content/52j87u2658171821/

Keep up to date

## 34th SEGH International Conference: Geochemistry for Sustainable Development

Victoria Falls, Zambia

02 July 2018

## SubmitContent

Members can keep in touch with their colleagues through short news and events articles of interest to the SEGH community.

## Science in theNews

Latest on-line papers from the SEGH journal: Environmental Geochemistry and Health

• Fertilizer usage and cadmium in soils, crops and food 2018-06-23

### Abstract

Phosphate fertilizers were first implicated by Schroeder and Balassa (Science 140(3568):819–820, 1963) for increasing the Cd concentration in cultivated soils and crops. This suggestion has become a part of the accepted paradigm on soil toxicity. Consequently, stringent fertilizer control programs to monitor Cd have been launched. Attempts to link Cd toxicity and fertilizers to chronic diseases, sometimes with good evidence, but mostly on less certain data are frequent. A re-assessment of this “accepted” paradigm is timely, given the larger body of data available today. The data show that both the input and output of Cd per hectare from fertilizers are negligibly small compared to the total amount of Cd/hectare usually present in the soil itself. Calculations based on current agricultural practices are used to show that it will take centuries to double the ambient soil Cd level, even after neglecting leaching and other removal effects. The concern of long-term agriculture should be the depletion of available phosphate fertilizers, rather than the negligible contamination of the soil by trace metals from fertilizer inputs. This conclusion is confirmed by showing that the claimed correlations between fertilizer input and Cd accumulation in crops are not robust. Alternative scenarios that explain the data are presented. Thus, soil acidulation on fertilizer loading and the effect of Mg, Zn and F ions contained in fertilizers are considered using recent $$\hbox {Cd}^{2+}$$ , $$\hbox {Mg}^{2+}$$ and $$\hbox {F}^-$$ ion-association theories. The protective role of ions like Zn, Se, Fe is emphasized, and the question of Cd toxicity in the presence of other ions is considered. These help to clarify difficulties in the standard point of view. This analysis does not modify the accepted views on Cd contamination by airborne delivery, smoking, and industrial activity, or algal blooms caused by phosphates.

• Effects of conversion of mangroves into gei wai ponds on accumulation, speciation and risk of heavy metals in intertidal sediments 2018-06-23

### Abstract

Mangroves are often converted into gei wai ponds for aquaculture, but how such conversion affects the accumulation and behavior of heavy metals in sediments is not clear. The present study aims to quantify the concentration and speciation of heavy metals in sediments in different habitats, including gei wai pond, mangrove marsh dominated by Avicennia marina and bare mudflat, in a mangrove nature reserve in South China. The results showed that gei wai pond acidified the sediment and reduced its electronic conductivity and total organic carbon (TOC) when compared to A. marina marsh and mudflat. The concentrations of Cd, Cu, Zn and Pb at all sediment depths in gei wai pond were lower than the other habitats, indicating gei wai pond reduced the fertility and the ability to retain heavy metals in sediment. Gei wai pond sediment also had a lower heavy metal pollution problem according to multiple evaluation methods, including potential ecological risk coefficient, potential ecological risk index, geo-accumulation index, mean PEL quotients, pollution load index, mean ERM quotients and total toxic unit. Heavy metal speciation analysis showed that gei wai pond increased the transfer of the immobilized fraction of Cd and Cr to the mobilized one. According to the acid-volatile sulfide (AVS) and simultaneously extracted metals (SEM) analysis, the conversion of mangroves into gei wai pond reduced values of ([SEM] − [AVS])/f oc , and the role of TOC in alleviating heavy metal toxicity in sediment. This study demonstrated the conversion of mangrove marsh into gei wai pond not only reduced the ecological purification capacity on heavy metal contamination, but also enhanced the transfer of heavy metals from gei wai pond sediment to nearby habitats.

• Cytotoxicity induced by the mixture components of nickel and poly aromatic hydrocarbons 2018-06-22

### Abstract

Although particulate matter (PM) is composed of various chemicals, investigations regarding the toxicity that results from mixing the substances in PM are insufficient. In this study, the effects of low levels of three PAHs (benz[a]anthracene, benzo[a]pyrene, and dibenz[a,h]anthracene) on Ni toxicity were investigated to assess the combined effect of Ni–PAHs on the environment. We compared the difference in cell mortality and total glutathione (tGSH) reduction between single Ni and Ni–PAHs co-exposure using A549 (human alveolar carcinoma). In addition, we measured the change in Ni solubility in chloroform that was triggered by PAHs to confirm the existence of cation–π interactions between Ni and PAHs. In the single Ni exposure, the dose–response curve of cell mortality and tGSH reduction were very similar, indicating that cell death was mediated by the oxidative stress. However, 10 μM PAHs induced a depleted tGSH reduction compared to single Ni without a change in cell mortality. The solubility of Ni in chloroform was greatly enhanced by the addition of benz[a]anthracene, which demonstrates the cation–π interactions between Ni and PAHs. Ni–PAH complexes can change the toxicity mechanisms of Ni from oxidative stress to others due to the reduction of Ni2+ bioavailability and the accumulation of Ni–PAH complexes on cell membranes. The abundant PAHs contained in PM have strong potential to interact with metals, which can affect the toxicity of the metal. Therefore, the mixture toxicity and interactions between diverse metals and PAHs in PM should be investigated in the future.