Heavy metals contamination, potential pathways and risks along the Indus Drainage System of Pakistan

Riverine water exposed to heavy metals (HMs) pollution is a major concern in the world because of its serious effects on ecosystem and human health. This study assessed the pollution status, sources, diffusion and potential risks of Mn, Co, Cu, Zn, Cr, Ni, Cd, Hg and Pb for the first time along the entire Indus Drainage System of Pakistan. The concentrations of nine HMs in the riverine water ranged from 5.05-101.59 μg/L with a mean value of 41.51 μg/L. The overall metals quantification along the drainage was significantly high (27% of the total) in River Chenab followed by River Indus (26%) > Soan (20%) > Ravi (19%) > Kabul (5%) > Swat (3%). The potential sources of contamination were identified to be the surrounding geogenic activities, industrial/municipal wastewater discharges, agricultural and surface runoffs by using multivariate statistics including metals correlation analysis, hierarchical cluster analysis and principal component analysis. The average mass flux of ∑HMs in the entire drainage was approximately 10.24 tons/year, to which the River Indus contributed 84% of the total, Chenab 11%, Ravi 3%, Kabul 1%, and Soan 1% with more prevalence of biological essential (Zn&Mn) and non-essential (Ni&Cr) metals. In terms of ecological risk, the riverine water metals contamination (1.59 to 57.06) was within the risk threshold (ERI < 110), while the risks of ∑carcinogenic metals for exposed children and adults along the basin were significantly influenced between acceptable to high cancer risk by Cd, Co, Ni, Cr and Pb.