Importance of the Geochemistry of Nearshore Sediments in the Realm of Heavy Metal Pollution Assessment

Estuarine and nearshore sediments are derived from multiple sources, such as rivers, flocculants generated through interaction of river water and groundwater with the seawater, diagenetic remobilization/re-suspension of sediments, landward transport of marine sediments and atmospheric deposition. Hence, estuarine sedi-ments are much complicated in their chemistry because of the dynamics and chem-ical processes involved in their formation combined with anthropogenic inputs. It is generally assumed that different types of materials including anthropogenic contam-inants transported from rivers are deposited in the ocean. However, such materials are either removed, modified, re-suspended and often remobilized in the nearshore envi-ronment before transporting to the open ocean or high seas. Owing to better infras-tructural facilities available on the world’s coasts, large cities developed around this region. Hence, the nearshore environments are increasingly polluted particularly after the industrial revolution. The nearshore environment is a fertile zone with abundant supply of nutrients and micro-nutrients like trace elements, which facilitates increase of primary productivity and connected fishery resource. In this study, an overview is provided to understand the ultimate fate of chemical components that are transported from rivers to the marine environment through estuaries, deltas and coastal regions to the marine environment around the Indian subcontinent. This study shows that the east coast of India is fairly pristine with regard to heavy metal pollution in the deltaic sediments when compared to the west coast of India because of the huge discharge of sediment and water from the Himalayan and Peninsular rivers of India. The sediments of the west coast have higher concentrations of Cd, Pb, Zn, Cu and Cr due to human activity. Specifically, Cd and to some extent Zn are higher in most of the reported studies, suggesting the impact of human activity. In addition, there is a need to understand chemical processes operating in the sub-surface environment in the coastal zone, such as coastal groundwater and seawater interactions. In order to attain sustainable development, it is suggested to delineate the zone of effluent discharge point from the river-estuarine system to avoid the return of contaminants back into the estuarine zone. Therefore, it is very important to understand the estu-arine geochemical processes and terrigenous matter together with the anthropogenic impacts for attaining sustainable development in the coastal zone.