Three Decades of Change in Potentially Toxic Elements in Brown Algae in the Northeast Atlantic Ocean

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 <i>Fucus ceranoides</i>, <i>F. spiralis</i>, and <i>F. vesiculosus</i> 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 <i>Fucus</i> 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.