Hydrogeochemical characterization and ecological risk screening of heavy metals in the Bagmati River, Kathmandu Valley, Nepal.

Abstract

The key characteristics of physicochemical parameters, their possible sources, and the extent of potential ecological risks posed by heavy metals in the core urban area of the Bagmati River, Kathmandu Valley, Nepal, were studied through the proxy screening of the river water in dry season. Heavy metals were analyzed by flame atomic absorption spectrometer. The concentrations of NO₃^-, PO₄^3-, NH₃, Cl^-, and heavy metals demonstrate the influence of anthropogenic activities in the river. The significant positive loadings of K⁺, NH₃, NO₃^-, and moderate loading of Na⁺ in a principal component reflect the influence of agricultural runoff and fertilizers. Gibbs diagram suggests the dominance of rock-water interaction in the river. United States Salinity Laboratory diagram, Kelly's ratio, and permeability index indicate that the river water is not suitable for irrigation. The mean pollution load index of 2.08 depicts that the river is contaminated by heavy metals based on their background natural concentration. The mean potential ecological risk index (E_rⁱ) of Cd is 49.39, indicating the existence of moderate ecological risk in the river. The order of E_rⁱ is Cd > Fe > Zn > Cr.