Increased atmospheric thallium threats to populated areas: A mini review

Air pollutants combined with Hg, Cd, Cr, Pb, etc. in many global populated areas were studied comprehensively, while our understanding towards thallium (Tl), an extremely toxic heavy metal, remains very limited. Further, the knowledge on atmospheric emissions, distribution, and the hidden risks associated with Tl is of great scarcity. Hence, this work aims to review recent data on significant sources of ambient Tl resulting from industrial activities, including Pb/Zn/Cu/Fe sulfide ore smelting, steel-making, coal burning, and cement production that involves the use of Tl-bearing wastes. Through the examination of Tl emissions and transfer pathways in the atmosphere, it is found that Tl is present at lower than ng/m³ in aerosols and air particulates but can increase to much higher levels even at 1000 μg/m³ in atmospheric fine particulate matters near the mining and smelting industrialized zones located near populated areas. This study highlights the importance of creating a comprehensive emission inventory for Tl, particularly in developing countries where this data is currently lacking. The time has come to develop a precise national emission inventory for Tl in order to prevent and mitigate the risks associated with ambient exposure to this element. This review offers novel insights for the scientific community and policy-makers in establishing effective control and management strategies to curb hidden Tl hazards derived from industrial activities.