Black Carbon Facilitated Transport of Lincomycin, Oxytetracycline, and Sulfamethoxazole in Saturated Sand.

Increasing concentrations of antibiotics in agroecosystems contributes to proliferation of antibiotic resistant bacteria, which is becoming a global threat to human health and food safety. Black carbon (BC), a carbonaceous geosorbent with strong sorption capability to antibiotics, has great potential to sequester antibiotics and thereby reduce their environmental transport, if added into soils. Nonetheless, BC may also facilitate the transport of antibiotics when BC particles are mobile in soils, especially for BC colloids that have greater antibiotics sorption ability and environmental mobility as compared with bulk-sized particles. A better understanding of facilitated transport of antibiotics by BC colloids in soils is essential to develop antibiotics mitigation strategy. In this study, we conducted column breakthrough experiments to investigate the effects of ionic strength on subsurface transport of antibiotics (i.e., lincomycin, oxytetracycline, and sulfamethoxazole) through saturated quartz sand in the absence and presence of BC colloids. The breakthrough curve results showed that in the absence of BC colloids, lincomycin transport increased with increasing ionic strength, whereas there was no effect of ionic strength on the transport of sulfamethoxazole and oxytetracycline. Under ionic strength of 0.1 to 10 mM, approximately 100% of injected sulfamethoxazole passed through the column, and 100% of injected oxytetracycline was retained in the column. In the presence of BC colloids, about 90% of lincomycin, oxytetracycline, and sulfamethoxazole were sorbed by BC colloids and co-transported through the column. The colloid-facilitated transport of lincomycin, oxytetracyclin, and sulfamethoxazole decreased with increasing ionic strength due to enhanced deposition of BC colloids under higher ionic strength. Our results clearly showed that the facilitated transport of antibiotics by BC colloids would enhance the transport and mobility of antibiotics in the environment.