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.