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 I-129 is a major fission product, highly volatile, spreads globally and is, therefore, a perfect tracer of human nuclear contamination. Atmospheric levels of I-129 were investigated by mosses and lichens from the southern Tibetan Plateau (STP). I-129 levels of (203 +/- 274) x 10(6) atoms/g and (175 +/- 142) x 10(-10) for I-129/I-127 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). I-129 discharge history in combination with the wind field analysis indicates that Indian NFRPs are the primary sources of I-129 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 I-129 and I-127 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 I-129 and other volatile airborne radioactive pollutants to the STP.