Wide exposure of persistent organic pollutants (PoPs) in natural waters and sediments of the densely populated Western Bengal basin, India

Abstract

Drinking water stress in South Asia is now widely known as a global paradigm. Extensive geogenic groundwater pollution is known in this area for a long time, specifically in the densely populated (~40 million) Western Bengal basin (WBB) of the state of West Bengal, India. Though anthropogenic-sourced groundwater pollution has been long suspected, it has been only sporadically reported thus far. The present study provides one of the first documentation of widespread existence and distribution of persistent organic pollutants [PoPs, e.g. pesticide (2014-2016) and polycyclic aromatic hydrocarbons (PAHs) (2015)] in the Ganges river (32 locations) water and groundwater (235 locations) of the WBB. All locations were found to have at least one of the 40 detected pesticides [predominated by Atrazine (0.95-3.93 μg/L) and Malathion (150-9330 μg/L)], their derivatives [e.g. Malaoxon (410-1420 μg/L)] and/or 16 PAHs [e.g. Naphthalene (4.9-10.6 μg/L), Phenanthrene (3.32-6.61 μg/L)]. Atrazine and Malathion were found to have concentrations up to 46 times higher than the permissible limits. Similar to pesticides in water, most of the sediment samples investigated obtain Malathion (56-200 μg/kg), malaoxon (>900 μg/kg). Sediment samples collected from 10-20 cm to 20-30 cm depth showed total PAHs concentration of 2.02 and 1.95 μg/kg respectively. While herbicides were found to be more common in agricultural areas, insecticides and PAHs dominate in urban areas, suggesting land-use to be an important controlling factor. An estimated 53% of urban and 44% of rural residents (~20 million total residents, including those in cosmopolitan areas of Kolkata) are potentially exposed to PoPs pollution in drinking water, in addition to much ill-famed geogenic, groundwater arsenic pollution exposure known from this area.

Keywords: Groundwater; Land-use; River water; Sediment; Western Bengal basin.