Survey of pharmaceutical contamination and antimicrobial activity in seawater along Tokyo Bay

To clarify the extent of seawater pollution by human waste in Tokyo Bay, pharmaceutical concentrations were analyzed using LC-MS/MS, and antimicrobial activity was assayed using the disk diffusion method. Four pharmaceuticals, diphenhydramine, clarithromycin, carbamazepine, and bezafibrate, were detected in Tokyo Bay seawater. Their concentrations were low near the bay mouth and increased toward the Tokyo waterfront. At Kasai Marine Park, a registered wetland under the Ramsar Convention for the protection of wild bird habitats located along the Tokyo waterfront, the maximum concentration of clarithromycin (72.4 ng/L) exceeded the predicted no-effect concentration (69 ng/L), indicating potential ecological risks. Meanwhile, at Odaiba Marine Park, a beach used for bathing and water sports, also situated along the Tokyo waterfront, the mean concentrations of the four pharmaceuticals in seawater were higher than those at Kasai Marine Park; however, none were considered to pose a risk to human health. Furthermore, antimicrobial activity was detected in seawater extracts collected from both parks. This activity cannot be explained solely by clarithromycin, the most frequently prescribed antibiotic, suggesting the involvement of multiple antimicrobial substances. To prevent adverse ecological effects of pharmaceutical contamination in seawater, it is necessary not only to decompose pharmaceuticals in sewage treatment plants but also to refrain from using unnecessary pharmaceuticals and to dispose of them through sewer systems.