Predicting mass loadings of sulfamonomethoxine, sulfamethoxazole, and lincomycin discharged into surface waters in Japanese river catchments

Abstract

Japanese strategies for the management of livestock waste suggest effluent discharge from livestock farms as major pathways of entry of veterinary antibiotics into surface waters. To aid control of their sources, we developed a model for predicting annual loads of antibiotics discharged into surface waters as effluent from livestock farms, sewage treatment plants, and households, using population, usage, excretion, removal, and fraction of livestock waste treated as wastewater. To verify the model, we monitored three antibiotics which are much used for livestock in Japan and are stable during river transport—i.e., sulfamonomethoxine (SMM), sulfamethoxazole (SMX), and lincomycin (LCM)—over one year in the Oyodo River, which has the most active swine farming area in Japan in its catchment. Concentrations and mass flows of SMM and SMX showed a sharp peak in winter, and those of LCM were also higher in winter than in summer in the river. Annual mass flows observed in the river and reported in three other Japanese rivers were within a range of ½ to 2 times the model estimates. Effluent from swine farms contributed largely to mass flows of SMM and LCM in the rivers, while human wastewater from sewage treatment plants and households contributed partly to substantially to those of SMX. Estimated contributions of surface runoff from agricultural land to the annual mass flows in the rivers were < 1%, in agreement with the prediction made by limiting sources to effluent. Although other locations and antibiotics should be studied in the future, this first attempt at modeling the load of veterinary antibiotics discharged from livestock farms provides a new perspective on how to reduce movement of these compounds into surface waters in catchments where wastewater treatment is or could be used in managing livestock waste. • A model of veterinary antibiotics in effluents was developed. • Observed riverine flux of SMM, SMX, and LCM increased in winter in a river. • The model estimates agreed well with annual mass flows of the antibiotics in rivers. • Effluent from swine farms was the largest source of the antibiotics. • Agricultural land was a negligible source of the antibiotics.