Unveiling the hidden ecological risks of emerging entangled with legacy pollutants within coastal-marine interfaces

Coastal-marine interfaces (CMIs) serve as critical biogeochemical transition zones, where terrestrial and oceanic systems intersect, and legacy and emerging contaminants frequently interact through sorption/desorption, precipitation/dissolution, and redox-mediated processes. However, the mechanisms by which these interactions perturb elemental cycling remain fragmented. This study conducts a comprehensive bibliometric synthesis of more than 5,000 peer-reviewed studies, integrating co-citation networks, keyword co-occurrence analysis, and spatial hotspot mapping, with a focused assessment of China's heavily contaminated coastal aquifers. The present analysis reveals that the co-transport and transformation of legacy and emerging contaminants in CMIs are jointly governed by hydrodynamic forcing, mineral surface reactivity, and redox gradients. Competitive interactions at Fe/Mn (hydr)oxide surfaces can enhance the mobility of trace metals such as Pb2+ and Cd2+. Microplastics function as reactive vectors that facilitate metal transport, while antibiotics disrupt key microbial guilds, particularly denitrifiers, thereby altering the cycling of carbon, nitrogen, phosphorus, and silicon. Moreover, redox transitions driven by submarine groundwater discharge (SGD), as freshwater mixes with saline porewater, induce reductive dissolution of Fe(III) oxides, mobilizing arsenic and amplifying nitrate fluxes to coastal waters. Three priority knowledge gaps are highlighted: (1) the interfacial processes linking microbes, organic matter, and minerals that control cross-media contaminant transfer; (2) the quantitative contribution of SGD to marine elemental budgets and the associated in situ geochemical transformations within subterranean estuaries; and (3) the feedback between climate change and multi-contaminant stress on coupled biogeochemical cycles. This review establishes a process-oriented framework for future research integrating biogeochemical and ecological dimensions in anthropogenically pressured CMIs.