137Cs and natural radionuclides in Antarctic soil-vegetation systems on King George Island: Contrasting patterns in penguin-influenced and reference habitats.

Fallout radionuclides are useful tracers of contaminant retention and redistribution in polar soil-vegetation systems. This study examined activities of 137Cs, 40K, total 210Pb, 226Ra, and 228Ac, together with δ15N and δ13C, in soil, penguin guano, lichens, mosses, and vascular plants collected during four campaigns over two austral spring-summer periods on King George Island. Relatively high 137Cs activities were observed in soil and Deschampsia antarctica in the penguin-influenced area, whereas Usnea antarctica showed low 137Cs activity in both areas. Fresh penguin guano contained low 137Cs activity (∼1 Bq kg-1 d.w.) and was not a direct high-activity source at sampling. D. antarctica showed consistently higher 137Cs activity in the penguin-influenced area than at the reference site across matched campaigns, together with a higher median soil-to-vegetation transfer factor, providing the clearest site-related 137Cs contrast among the analysed vegetation groups. U. antarctica showed the highest total 210Pb activity, while 7Be was detected in three lichen samples, a pattern compatible with atmospheric particle interception. Lower δ15N in U. antarctica was consistent with weaker ornithogenic nitrogen influence. Together, the contrasting radionuclide profiles indicated a stronger substrate-associated 137Cs signal in D. antarctica, whereas the U. antarctica profile was more compatible with atmospheric particle interception.