The Return of Natural Lead to the Northeast Atlantic Ocean Captured by Brown Algae

Lead (Pb) is a highly toxic pollutant with serious ecological implications. This study investigates 30-year trends (1990-2021) in Pb concentrations and isotopic signatures (²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁶Pb) in the brown algae Fucus spp. from the Northeast Atlantic Ocean (n = 446). Pb concentrations showed only modest, non-significant 21.9% decline. In contrast, isotopic data revealed a clear shift from anthropogenic to natural sources. Bayesian mixing models (MixSIAR) supported this trend, indicating an increase in natural contributions, rising from 4.7% in 1990 to 61.5% in 2021, mirroring reductions in coal combustion (from 48.4% to 6.3%) and petrol-related sources (from 46.9% to 32.2%). This divergence between concentrations and isotopic trends likely reflects a substantial increase in sediment-derived Pb (189.3% in 2021 compared to 13-49% during 1990-2007), as well as enhanced bioavailability driven by environmental changes such as ocean acidification. Elevated Pb levels were found in inner estuarine zones dominated by Fucus ceranoides, but no latitudinal pattern or isotopic differences among species were observed. Overall, the findings highlight the complex dynamics of Pb in coastal ecosystems and the limitations of relying solely on concentration data to assess pollution trends. Isotope analyses have proven essential for source attribution, revealing a progressive shift toward natural Pb sources and supporting the effectiveness of regulatory measures such as the global phase-out of leaded gasoline. However, the study underscores that increased Pb bioavailability, driven by acidification and other global environmental changes, may offset the benefits of reduced emissions. Finally, this work provides a valuable isotopic baseline for a region where such data remain scarce, supporting future environmental monitoring and source-tracing efforts.