Health risk assessment and spatial variations of dissolved heavy metals and metalloids in a tropical river basin system

摘要

River water is too much vulnerable to pollution as it is exposed to a large number of pollutants through natural and anthropogenic activities. Mahananda River is an important river in West Bengal and Bangladesh without having prominent research information about its water quality and pollution status and is likely to be under the threat of pollution by practical experience. The study was conducted to identify the dissolved heavy metals and metalloids in the water and their concentrations; to analyse metal(loid) pollution status through Nemerow index (Pn) and heavy metal pollution index (HPI); to evaluate the non-carcinogenic human health hazards by hazard index (HI) and to anticipate the incremental lifetime cancer risk (ILCR) by index analysis. For this purpose 54 samples were collected from 27 sampling stations in pre-monsoon and post-monsoon seasons. Eleven metal(loid) s (Mn, Cr, Fe, Cu, Zn, Ni, Co, As, Cd, Pb and Hg) were tested and identified with concentrations considerably below from their regulatory standards indicating safe for drinking purpose. Pearson's correlation analysis and principal component analysis (PCA) reveal the sources of these metal(loid)s as both geogenic and anthropogenic. HPI and HEI analysis permit the water as suitable for use but Pn index designates one sampling station as heavily polluted and a few stations as slightly polluted in pre-monsoon. HIAdult analysis reveals that seven sampling stations in pre-monsoon and two sampling stations in post-monsoon exceeded the limiting value (HI <= 1) of hazards. HIChild values were found greater than one (> 1) at six sampling stations in the pre-monsoon season. ILCR analysis predicts that 15 sampling stations (55.55%) in pre-monsoon and six sampling stations in post-monsoon have crossed the cancer risk limiting value (ILCR > 1.0x10(-4)). As the study area does not possess any heavy industries, the metal(loid) pollution occurs mainly from heavily populated municipal zones like Siliguri, Barsoi and Malda town. The pre-monsoon values of different indices are greater than the post-monsoon ones because of the low quantity of water available and flow rate that increase the concentrations of metal(loid)s in river water. Moreover, some pollutants are washed out with heavy water during monsoon season. These municipalities need sustainable management planning.