Potentially toxic elements in multi-stressor marine environments: bioaccumulation, ecosystem impacts, and human...

Potentially toxic elements pollution in marine environments is intensifying under anthropogenic activities and climate-driven changes, yet the interactive effects of multiple stressors on metal bioaccumulation, ecosystem health, and human risk remain inadequately synthesized. This review aims to quantitatively integrate multi-stressor interactions involving ocean warming, acidification, and eutrophication with potentially toxic elements dynamics across coastal, estuarine, and open ocean systems. Following PRISMA guidelines, 154 peer-reviewed studies from 652 screened records were synthesized to establish a comprehensive, evidence-based framework for predictive risk assessment. This review indicates that multi-stressor conditions fundamentally alter speciation and bioavailability of mercury (Hg), cadmium (Cd), lead (Pb), arsenic (As), and chromium (Cr), producing synergistic and other non-additive effects that amplify biomagnification. Methylmercury (MeHg) exhibits the strongest trophic magnification, with factors reaching 11.1 in polar shelf ecosystems, while cadmium and lead show biodilution yet elevated tissue burdens in benthic organisms under combined warming and acidification. Arsenic speciation shifts toward more toxic inorganic forms under acidification, and chromium bioavailability increases with pH-dependent redox changes. Sublethal effects, including reproductive impairment, oxidative stress, and metabolic disruption, cascade to population declines and impaired ecosystem functions, with early life stages exhibiting up to 40% greater sensitivity under combined exposures. Human health risk assessments reveal that seafood-consuming populations face elevated risks, with hazard quotients for mercury exceeding one in high-consumption groups, lifetime cancer risks from arsenic and cadmium surpassing safe thresholds, and lead and chromium contributing to cardiovascular and renal toxicities. These findings suggest that current regulatory thresholds, which overlook interactive effects and additive toxicities, systematically underestimate cumulative threats in a changing ocean, necessitating urgent adoption of integrated, climate-aware frameworks aligned with international instruments such as the Minamata Convention on Mercury to protect marine ecosystems and human health.