A comprehensive review on current status, mechanism, and possible sources of arsenic contamination in groundwater: a global perspective with prominence of Pakistan scenario.

Arsenic(As)-mediated contamination of groundwater resources in different parts of the world is a consequence of natural or anthropogenic sources, leading to adverse effects on the environment and human health. Millions of people from different countries are unfortunately consuming groundwater contaminated with alarming levels of As. Exposure to the high concentration of As for an extended period of time can cause devastating effects on human health such as skin lesions, cardiac disorders, discolouration and cancer. Until 2018, about 11 districts of Sindh and Punjab provinces in Pakistan had been found with As contamination in groundwater beyond the national defined permissible level, i.e. 50 µg/L. Tharparkar and Hyderabad (in Sindh province) along Indus river and Lahore and Kasur (in Punjab province) are well-known hotspots sites of natural geogenic As contamination in groundwater. Higher levels of Sulfates (SO), Chloride (Cl) and Carbonate (CO) along with the elevated values of electrical conductivity and basic pH, as well as augmented presence of "As V" species, were all an indication of oxidizing condition in groundwater, and these oxidizing conditions are identified as the primary mechanism of As contamination into aquifers of Pakistan via oxidative dissolution. The main aim of this review is to summarize and discuss the current contamination status of As in groundwater water globally with a special focus on Pakistan scenario, isotopic evidence to track sources of groundwater recharge and its effects on As contamination in groundwater with various redox conditions prevailing in Pakistan. In addition, public health consequences of As contamination and mitigation strategies for As removal from water resources have been also highlighted. In this review, the data were extracted from various cutting edge studies published in national and international journals.