Occurrence, source identification and potential risk evaluation of heavy metals in sediments of the Hunza River and its tributaries, Gilgit-Baltistan

The present study examined heavy metals concentrations in sediments of the Hunza River and its tributaries, Gilgit-Baltistan, Pakistan. For this purpose, surface sediments were sampled from the Hunza River and its tributaries along with the three main geological units i.e. Wakhan Block (upstream), Karakoram Block (midstream) and Kohistan Block (downstream). Heavy metals concentrations in each sample were analyzed using the atomic absorption spectrometry (AAnalyst 700, PerkinElmer, USA). Results showed the highest mean concentration for iron (Fe, 44400 mg/kg) and the lowest was observed for cadmium (Cd, 0.62 mg/kg). Heavy metals concentration showed an increasing trend in sediments with the downward flow and resulted in higher values along the Kohistan Block (downstream) and lowest in the Wakhan Block (upstream). Determined heavy metals concentration were evaluated for the pollution quantification factors. The values of contamination factor (CF) and pollution load index (PLI) showed heavy metals contaminations in the sediment of the Hunza River and its tributaries. The highest (175) values of ecological risk index (ERI) were observed for Cd and classified at a moderate-risk level to the aquatic ecosystem. Statistical analyses revealed that natural denudation of bedrock and mineralized zone led to heavy metal contamination in sediments of the Hunza River and its tributaries with lesser input from anthropogenic activities. (C) 2020 Elsevier B.V. All rights reserved.