Nationwide monitoring of selected antibiotics: Distribution and sources of sulfonamides, trimethoprim, and macrolides in Japanese rivers

We report the results of a nationwide survey of commonly used human and veterinary antibiotics (7 sulfonamides, trimethoprim, and 4 macrolides) in 37 Japanese rivers. Concentrations of the sum of the 12 target antibiotics ranged from undetectable to 626 ng/L, with a median of 7.3 ng/L for the 37 rivers. Antibiotics concentrations were higher in urban rivers than in rural rivers and were correlated with those of molecular markers of sewage (crotamiton and carbamazepine). Macrolides were dominant over sulfonamides in urban rivers. Sulfonamides, especially sulfamethazine (used in animals), were dominant in a few rivers in whose catchment animal husbandry is active. However, these signals of veterinary antibiotics were overwhelmed by those of human antibiotics in lower reaches of most rivers. The analysis of the antibiotics in all 88 samples showed that the target antibiotics in Japanese rivers are derived mainly from urban sewage, even though larger amounts of antibiotics are used in livestock. Most of the livestock waste-derived antibiotics are unlikely to be readily discharged to surface waters.