Hydrochemical characteristics, trace element sources, and health risk assessment of surface waters in the Amu Darya Basin of Uzbekistan, arid Central Asia

Thorough knowledge of hydrochemical characteristics and trace element concentrations in surface waters is crucial for protection of this resource, especially in arid regions. Uzbekistan lies in central, arid Central Asia, and is experiencing severe water scarcity as a consequence of warming climate and accelerated human impacts. Fifty-five surface water samples were collected from the Amu Darya Basin of Uzbekistan (ADBU) and measured for relevant variables, to determine hydrochemical characteristics and evaluate water quality. River water samples from the middle reach and Amu Darya Delta (ADD) were dominantly HCO3-Ca and SO4-Ca·Mg types, respectively, whereas water samples collected near the former shoreline and sewage outlets in the ADD were predominantly Cl-Ca·Mg and Cl-Na types, consistent with the distribution of sites that display high concentrations of trace elements and are seriously affected by human activities. Principal component analysis indicated that Pb and Cd in surface waters of the ADBU had industrial origins. Local agricultural activities are thought to have contributed to the concentrations of NO3, Zn, Ni, Hg, and Mn, through pesticide and fertilizer applications, and concentrations of Cu, Cr, As, and Co are controlled by mixed natural and anthropogenic sources. Water quality and health risk assessments indicated that unsuitable drinking waters are distributed mainly near the former shoreline and sewage outlets in the ADD, making human health risks in these areas high.