Mercury in Antarctic vegetation as an indicator of uptake routes and bioavailable forms

Mercury (Hg) is a global contaminant of concern due to its persistence, toxicity, and capacity for long-range transport. This study investigated the Hg concentration, chemical speciation, and δ¹³C/δ¹⁵N stable isotope signatures in Antarctic coastal flora, comprising lichens, mosses, vascular plants, and algal mats (Prasiola crispa) to evaluate the relative importance of atmospheric, edaphic, and biogenic inputs in Hg accumulation. Samples were collected from King George Island during the austral summer of 2018/19. Lichens showed the highest Hg concentration (median THg = 116.6 ng g⁻¹) and an elevated MeHg fraction (17 %), reflecting long-term atmospheric accumulation. Mosses contained substantially lower Hg concentration (median 31.8 ng g⁻¹; MeHg = 8 %), consistent with predominantly atmospheric inputs. Vascular plants exhibited only trace Hg concentration (median 22.8 ng g⁻¹; MeHg = 2 %), with multiple lines of evidence suggesting a major contribution of soil-derived inputs under ornithogenic influence. P. crispa mats showed intermediate THg concentration (median 39.7 ng g⁻¹; MeHg = 6 %) and strong δ¹⁵N enrichment, suggesting exposure to guano-derived nutrients and being consistent with hydrological transport of predominantly inorganic Hg. These patterns reveal distinct Hg exposure pathways among Antarctic vegetation and highlight their value as sentinels of atmospheric and biogenic Hg inputs. The findings enhance understanding of Hg dynamics in polar terrestrial ecosystems and underscore the need for future studies integrating Hg isotopes and targeted microbial methylation markers (e.g., hgcA/hgcAB), together with direct hydrological measurements (e.g., runoff and soil-water Hg), to better resolve sources, transport and potential transformation pathways.