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Is the Indian Sundarban and adjacent regions polluted by mercury? A case study and cross sectional view

05 June 2014
The Indian Sundarban and its adjacent regions are experiencing huge population loads in terms of domestic and industrial effluents from upstream highly urbanized Calcutta and surroundings

 

The Indian Sundarban comprises 40% of the largest delta formed at the confluence of Bay of Bengal by sedimentation of River Ganges and its tributaries. The region is a unique ecosystem type comprised of mangrove wetlands, tidal creeks, lowlands and mudflats. The main occupation of the coastal population is mainly farming and fishing with some others. The Indian Sundarban and its adjacent regions are experiencing huge population loads in terms of domestic and industrial effluents from upstream highly urbanized Calcutta and surroundings. The region is comparatively less explored in terms of ecological and toxicological health hazards. During the last two decades a number of studies have revealed the pollution status of this important region confirming that the region is getting contaminated by a number of pollutants. These include heavy metals, persistent organic pollutants, organotins in biotic and abiotic compartments of the ecosystem.


Mercury is among the toxic heavy metals considered as one of the priority pollutants by international agencies. Mercury has the ability to enter the food chain in the form of organo-mercury (methyl, ethyl) and biomagnify in higher trophic levels. So human corresponding to the higher trophic positions depended on fish meal for protein and Omega-3 fatty acids are at higher risk from mercury. After the incidence of Minamata, Japan raising concerns on the health impacts of mercury on biota and human beings from fish consumption on global scale. There is very little known about the mercury contamination and human exposure in Indian Sundarban which houses about 172 species of fishes and majority of the population depends fish as a major protein source. With this objective a collaborative research work was undertaken with the Centre for Environmental Geochemistry at the British Geological Survey, funded by the Commonwealth Scholarship Commission UK, to perform a case study of mercury pollution in abiotic (sediment) and biotic matrices of Indian Sundarban and adjacent regions.

The samples were collected based on the standard protocols and availability of the biota. The HgT was measured using The Total mercury analyzer (TMA, Milestone). As expected, the sediment was lowest in HgT concentration (0.008 µg g-1 to 0.056 µg g-1). The trend of HgT accumulation in biota was polychaete>fish>bivalve mollusks. Since mercury (in the form of methylmercury) bioaccumulates along the food chain, it was expected that fish would have highest values of HgT among the biota because of its higher trophic position. However, in this study trophic position was not proved to be the key factor to control HgT accumulation. Also the habitat preference (e.g., deposit feeders) could be an important factor for determining the HgT concentration in biota. However, among fishes, carnivorous species tend to accumulate high HgT than that of others. Also the diet (i.e., proportion of feed like polychaetes as food) and exposure time to mercury are important factors controlling HgT concentration. The study revealed that the HgT concentration was lower compared to other studies in the world. Although the overall concentration is low due to a number of operational factors, the highest concentration in biota (polychaete) revealed above the prescribed values, indicating further extensive studies (2014).

A cross-sectional study to ascertain the human exposure of HgT was done by Chatterjee et al., (in press). In this study the authors performed a survey and analysis on the local coastal residents (Sagar Island, Sundarban, India), majority of whom are fisherfolks. The study mainly focused on the human exposure of HgT (via hair biomarker analysis) in terms of fish intake (via dietary survey). In this study, fishes showed low mercury values (0.01-0.11 µg g-1 dry weight) while hair mercury ranged from 0.25- 1.23 µg g-1 dry weight. Hair mercury concentration was highly correlated with the fish consumption frequencies. We didn’t find any influence of age, gender and occupation on the mercury levels. The concentration of HgT in scalp hair revealed baseline information on mercury exposure of fisherfolk population in Indian Sundarban. We need further study considering more participants of different socio-economic groups and diet patterns to comment on the human exposure status of mercury in this region.

Dr. Chatterjee is now a Research Associate in Divecha Centre for Climate Change, Indian Institute of Science, Bangalore, India.

Dr. Mousumi Chatterjee, (maussim@gmail.com) former CSIR research associate in Department of Marine Science, University of Calcutta, India

References

Chatterjee M, Sklenars L, Chenery S R, Watts M J, Marriott A L, Rakshit D, Sarkar S K. (2014). Assessment of Total Mercury (HgT) in Sediments and Biota of Indian Sundarban Wetland and Adjacent Coastal Regions, Environment and Natural Resources Research, 4, 2, 50-64. http://www.ccsenet.org/journal/index.php/enrr/article/view/31996

Kwokal, Z., Sarkar, S. K., Fransiškovic-Bilinski, S. W., Bilinski, H., Bhattacharya, A., Bhattacharya, B. D., & Chatterjee, M. (2012). Mercury concentration in sediment cores from Sundarban mangrove wetland, India, Soil and Sediment Contamination An International Journal, 21(4), 525-544. http://dx.doi.org/10.1080/15320383.2012.664185

Antizar-Ladislao,B., Sarkar, S, K., Anderson, P., Peshkur, T., Bhattacharya, B.D., Chatterjee, M., Satpathy, K. K. (2011). Baseline of butyltin contamination in sediments of Sundarban mangrove wetland and adjacent coastal regions, India. Ecotoxicology 20:1975–1983. DOI 10.1007/s10646-011-0739.

Chatterjee, M., Canario, J., Sarkar, S. K., Branco, V., Bhattacharya, A., & Satpathy, K. K. (2009). Mercury enrichments in core sediments in Hugli–Matla–Bidyadhari estuarine complex, north-eastern part of the Bay of Bengal and their ecotoxicological significance. Environmental Geology, 57, 1125-1134. http://dx.doi.org/10.1007/s00254-008-1404-z

Chatterjee, M., Silva-Filho, E. V., Sarkar, S. K., Sella, S. M., Bhattacharya, A., & Satpathy, K. K. (2007). Distribution and possible source of trace elements in the sediment cores of a tropical macrotidal estuary and their ecotoxicological significance. Environment International, 33, 346-356. http://dx.doi.org/10.1016/j.envint.2006.11.013

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