Contrast antibiotic activities from muddy and sandy coasts and their potential controls.

Muddy and sandy coastlines account for approximately 45% of the world's ice-free coastlines, facing significant ecological risks from antibiotic pollution due to overuse. This study elucidates how fundamental differences in sediment composition govern the distinct transport and fate of antibiotics in these contrasting coastal systems. Muddy coasts primarily consisted of fine-grained sediments with higher water contents, whereas sandy coasts are characterized by coarse-grained sand and gravel with better water permeability. Porewater acts as a bridge between overlying water and sediment, playing a crucial role in contaminant transport. This study compared the antibiotic pollution patterns and revealed the regulatory mechanisms of coastal sediment on the antibiotic source - sink processes. Results showed that antibiotic concentrations in the porewater of mangroves (18.4-182 ng/L) were significantly higher than those (13.3-30.4 ng/L) in sandy beaches. However, higher proportions of tetracyclines in sandy sediment porewater than muddy sediment porewater were found. Spatially, the lowest antibiotic concentrations within the mangrove ecosystem occurred in natural areas. Source analysis indicated that antibiotics in mangroves were predominantly derived from localized sewage and wastewater, whereas in sandy beaches, they were primarily attributed to non-point sources via rainfall runoff and tidal forcing. Our findings revealed that sediment properties govern the spatial distribution and ecological risks of antibiotics in coastal zones. The contrasting retention capacities of muddy and sandy coasts dictate divergent ecological risk patterns. An accurate assessment of the environmental risks posed by antibiotics must account for their specific behavior in water-sediment systems. Consequently, management for muddy coasts should emphasize source control, while for sandy coasts, priority should be given to intercepting transport pathways.