Dominant geochemical reactions and hazardous metal contamination status in the Kabul’s aquifers, Afghanistan

Abstract

Water is an essential resource for all people, particularly those who live in arid areas, such as Kabul city, Afghanistan. In last decade, development of academic communities and contribution from international organizations have provided opportunities for researchers to address the environmental issues, including problems related to drinking water in Kabul city. Although most of these researches focused on the capital, due to shortage of financial support for water quality studies as well as security concerns, there are in fact very limited publications in that area of interest. Based on an extensive literature search and comprehensive review, four major processes have been identified as controlling factors for water quality in the studied area, which include mineral weathering, redox-sensitive processes, role of adsorption/desorption, and effects of NO3 influx. Among these factors, the most important one was the redox-sensitive processes that have considerable impacts on the chemical composition of water reserves in the Kabul area. Even though there are significant inputs of domestic sewage that released protons into the aquifers, the presence of carbonates with a great buffering capacity has prevented the dissolution of most pH-sensitive minerals; in most cases, these minerals contain hazardous metals. In terms of metal contamination in the Kabul Basin, three metals have displayed elevated levels above the World Health Organization guidelines: uranium, arsenic, and nickel. Based on the literature review, the origin of these toxic metals has revealed, and the associated weathering reactions are presented.