Trophic magnification of antibiotics in a coral reef food web from the South China Sea: Bioaccumulation, source apportionment, and human health risks.

Antibiotic contamination in coral reef ecosystems remains poorly understood, particularly regarding its sources, transfer through the food chain, and ecological and dietary risks. This study examined 33 antibiotics in seawater, sediments, suspended particulate matter (SPM), and marine organisms from Qingshui Bay, a tropical coral reef-associated coastal system in southern Hainan Island, China. Twenty-five antibiotics were detected in seawater, while 22 were found in sediments and SPM. Average concentrations were 41.6 ng/L in seawater, 24.2 ng/g dw in sediments, and 38.83 ng/g dw in SPM. Quinolones were the dominant antibiotic class, accounting for 71.2%, 84.1%, and 78.4% of the total in each matrix. Spatial analysis showed slightly higher contamination near the reef and shore than offshore, indicating land-based and aquaculture inputs. Source analysis using principal component analysis (PCA) and positive matrix factorization (PMF) identified aquaculture, livestock, and domestic wastewater as major sources. In marine organisms, 28 antibiotics were detected, averaging 87.6 ng/g dw, with fish and cephalopods exhibiting relatively higher residue levels and bioaccumulation factors than crustaceans and mollusks. Ciprofloxacin and norfloxacin showed strong bioaccumulation potential; six antibiotics demonstrated trophic magnification (trophic magnification factors > 1). Ecological risk assessment indicated low overall risks, with only norfloxacin and sulfadiazine presenting minor concerns in seawater. Dietary risk assessment suggests minimal impact on human health through seafood consumption. This is the first multi-matrix study evaluating antibiotic presence, sources, bioaccumulation, trophic transfer, and risk in a southern Hainan coral reef ecosystem, providing essential baseline data for pollution management.