Long-Range Transboundary Transport of Iodine-129 from South Asia to the Southern Tibetan Plateau Revealed by Moss and Lichen

Level and transport regime of radioactive pollutants are scarcely understood at the remote high-altitude Tibetan Plateau (TP), which is the well-known third pole. Radioactive 129I is a major fission product, highly volatile, spreads globally and is, therefore, a perfect tracer of human nuclear contamination. Atmospheric levels of 129I were investigated by mosses and lichens from the southern Tibetan Plateau (STP). 129I levels of (203 ± 274) × 106 atoms/g and (175 ± 142) × 10–10 for 129I/127I atomic ratios were first presented in the STP, considerably greater than the prenuclear level, but 2–4 orders of magnitude lower than the areas surrounding Indian and European nuclear fuel reprocessing plants (NFRPs). 129I discharge history in combination with the wind field analysis indicates that Indian NFRPs are the primary sources of 129I in the STP, and the Indian summer monsoon played a crucial interactive role in transporting airborne radioactive pollutants from South Asia to the STP interior. The spatial distribution of 129I and 127I in lichens distributed across Mt. Galongla reveals that the Yarlung Zangbo Grand Canyon serves as a key transport channel. The findings provide a deep understanding of the origins and long-distance trans-boundary transport of both 129I and other volatile airborne radioactive pollutants to the STP.