Incidence of heavy metals and river restoration assessment of a major South Asian transboundary river.

Heavy metal contamination of river water has become a major issue affecting environmental and human health worldwide. This study makes an effort to observe the heavy metal incidence of River Brahmaputra, India, and its river restoration assessment for 2 years, 2017-2018 and 2018-2019. River Brahmaputra is the second longest and a major transboundary river of the South Asian region, which transcends the political boundaries of China, India and Bangladesh. The Pearson correlation analysis was used to analyse the interrelationships between physico-chemical parameters (which was also analysed during our study) and heavy metals. Heavy metal pollution index and multivariate analyses such as hierarchical cluster analysis and principal component analysis were used to establish our scientific observations. An assessment involving people's willingness to pay for river restoration was also done. Arsenic (As), lead (Pb), antimony (Sb), nickel (Ni), chromium (Cr), mercury (Hg) and cadmium (Cd) were monitored in three stations, namely, Dibrugarh Town (Tinkunia Ghat), Guwahati City (Bharalumukh) and Dhubri Town (Jahajghat), for the periods 2017-2018 and 2018-2019. The overall mean concentration was in the order Hg > Ni > Cr > Pb > Cd > As > Sb. Heavy metal pollution index was found in the order station 2 (344) > station 3 (320) > station 1 (317). Results clearly indicate the presence of heavy metal pollution in the Brahmaputra river, with very high levels in Guwahati City. Concentrations of Ni, Cr, Hg and Cd were found to be very high while As presence was marginally high. Concentration of Pb and Sb were nearly the prescribed World Health Organization and Bureau of Indian Standards limits. Multivariate analyses suggest that the heavy metal pollution is linked to similar sources in all the sampled sites. Further, the river restoration assessment revealed that citizens are willing to pay an average of INR 22.6 (USD 0.30) for restoring the water quality. Therefore, given the high levels of heavy metal contamination witnessed in the Brahmaputra river and citizens willingness to contribute towards restoring its water quality, the need for an appropriate river restoration strategy and water policy is strongly felt as an outcome of this study.