In the current scenario of global change, heavy metal pollution is of major concern because of its associated toxic effects and the persistence of these pollutants in the environment. This study is the first to evaluate the changes in heavy metal concentrations worldwide in brown algae over the last 90 years (>15,700 data across the globe reported from 1933 to 2020). The study findings revealed significant decreases in the concentrations of Cd, Co, Cr, Cu, Fe, Hg, Mn, Pb and Zn of around 60-84% (ca. 2% annual) in brown algae tissues. The decreases were consistent across the different families considered (Dictyotaceae, Fucaceae, Laminariaceae, Sargassaceae and Others), and began between 1970 and 1990. In addition, strong relationships between these trends and pH, SST and heat content were detected. Although the observed metal declines could be partially explained by these strong correlations, or by adaptions in the algae, other evidences suggest an actual reduction in metal concentrations in oceans because of the implementation of environmental policies. In any case, this study shows a reduction in metal concentrations in brown algae over the last 50 years, which is important in itself, as brown algae form the basis of many marine food webs and are therefore potential distributors of pollutants.

Marine pollution from potentially toxic elements (PTEs) threatens coastal ecosystems, making long-term assessments essential. This study analyzes trends in Al, Cr, Fe, Ni, Cu, Zn, As, Cd, and Hg using 446 samples of Fucus ceranoides, F. spiralis, and F. vesiculosus collected between 1990 and 2021 at 173 coastal sites in NW Spain. A consistent resampling approach revealed significant declines in most anthropogenic PTEs, including Cu (-84.7%), Cr (-84.6%), Hg (-49.6%), and Cd (-36.7%) over time. In contrast, arsenic increased by 36.1%, but the underlying causes remain unclear, with potential factors including changes in sediment inputs, bioavailability, or emerging sources such as groundwater discharges. Higher PTE levels were detected in inner estuarine areas, but no consistent latitudinal patterns emerged. Overall, the results suggest effective mitigation of coastal pollution, with reduced bioavailable PTEs entering the food web via Fucus spp. However, rising As levels and complex contamination dynamics underscore the need for continued monitoring. This study offers the most comprehensive standardized assessment of long-term PTE trends in brown algae to date, providing valuable insights for environmental policy and coastal management.

With the aim of further standardizing biomonitoring techniques with aquatic mosses, the relationship between the velocity of water flow and cadmium (Cd) accumulation in transplants of the moss Fontinalis antipyretica was investigated. For this purpose, moss transplants were exposed in a controlled aquatic environment to different concentrations of Cd (0, 4, 16 and 36 ng g⁻¹) and different water velocities (10, 30, 50, 70 and 90 cm s⁻¹). The Cd concentrations in the moss transplants mainly depended on the Cd concentration in the water, but a small fraction of the variance was explained by water velocity. The Cd concentrations in moss were standardized to remove the effect of the concentration in the water so all the data could be analyzed together. The regression model for the standardized concentrations explained 23% of the variance in Cd accumulation in F. antipyretica and water velocity proved to be a significant predictor of Cd accumulation.

Brown macroalgae are widely used as biomonitors of marine pollution, but their Potentially Toxic Element (PTE) composition has never been assessed through compositional data analysis (CoDA). This study presents the first comprehensive application of CoDA to characterize PTE patterns in brown algae worldwide. Across more than 1320 records, Zn consistently dominated tissue compositions (73.8 %), followed by Cu and Ni, while Pb and Cd contributed modestly and showed higher variability. Multivariate analyses revealed structured gradients in elemental composition, with taxonomic identity, particularly species, emerging as the strongest predictor of PTE profiles (R² = 33.9 %). Nevertheless, substantial heterogeneity remained across studies, underscoring the influence of local environmental conditions and methodological differences. This highlights the need for standardized protocols to improve comparability in long-term biomonitoring. Extended profiling of Fucus spp. revealed a pattern dominated by Fe (44.9 %) and Al (36.0 %), with Zn (8.78 %) and As (7.23 %) as secondary contributors, and trace levels of Cu, Ni, Cr, Cd, Pb, and Hg. Significant shifts in Fucus spp. compositional profiles were detected over three decades (1990-2021), with recent samples showing a marked increase in Al, and declines in Cu, Ni, and Cr, suggesting changes in particulate deposition and PTE availability. Compositional analysis proved effective in identifying outlier samples from contaminated sites. Altogether, our results demonstrate that PTE profiles in brown algae are not random but taxonomically structured, reflecting species-specific physiological capacities for PTE regulation as well as differences in habitat and ecological niche. Combining absolute and compositional approaches improves the sensitivity, robustness, and ecological relevance of biomonitoring and bioremediation assessments.

Mercury is a globally distributed pollutant with significant ecological impacts. Terrestrial mosses have been widely used as Hg biomonitors, however, the mechanisms governing Hg accumulation, retention and release in these organisms remain poorly understood. This knowledge gap hinders our ability to predict the ecotoxicological effects of Hg on mosses and to accurately interpret the results of biomonitoring. This study investigates the deposition pathways, sources, and molecular mechanisms driving Hg accumulation in Pseudoscleropodium purum integrating isotopic, chemical and molecular analyses. Our results showed that gaseous elemental Hg (Hg0) was the primary deposition pathway. Hg stable isotopes and chemical evidence failed to link Hg levels in mosses to local sources such as forest fires and coal combustion, or AMDEs, suggesting that long-range atmospheric transport was the prevailing source. Odd mass independent fractionation of Hg isotopes (e.g., Δ199Hg) revealed post-depositional photochemical reduction, leading to re-emission of Hg. Molecular analyses indicated that Hg accumulation in mosses is associated with an increase in amide groups and a concurrent decrease in carbonyl groups within the extracellular space¡. The reverse process, amide hydrolysis, would lead to the release of previously bound Hg. Our study provides new mechanistics insights into Hg loading and release in mosses, showing that functional groups in the cell wall and plasma membrane may act as barriers to cytosolic entry, likely mitigating toxicity. These findings challenge the assumption that mosses are reliable accumulative biomonitors, demonstrating instead that Hg content reflects a dynamic balance between deposition and photoreductive losses.