louds drifting across the lofty heights of the Himalayas are carrying toxic heavy metals, putting mountain communities and downstream populations at risk, according to new research from the Indian Institute of Technology Mandi and European partners.
Scientists collected “cloud water” samples near the Kangchenjunga massif at elevations above 4,000 m. Analysis showed concentrations of lead (Pb), arsenic (As), cadmium (Cd), nickel (Ni) and mercury (Hg) up to five times higher than World Health Organization guidelines for safe drinking water. Levels peaked during the pre-monsoon and post-monsoon periods, coinciding with intense crop residue burning and dust-laden winds from the Indo-Gangetic Plain.
“We were astonished to find such high metal loadings in what seems like pristine mountain air,” said Prof. Kiran Sharma, an atmospheric chemist at IIT Mandi and co-author of the study. “The Himalayas are acting like a giant filter—capturing pollutants emitted hundreds of kilometers away.”
Heavy metals emitted by coal‐fired power plants, industrial complexes and vehicle traffic in South Asia, China and Southeast Asia hitch a ride on seasonal winds. When these polluted air masses are forced upward by the region’s steep terrain, cooler temperatures condense contaminants into cloud droplets. Over time, glaciers and snowfields accumulate the toxic residues.