Assessment of soil to mitigate antibiotics in the environment due to release of wastewater treatment plant effluent

With low levels of human antibiotics in the environment due to release of wastewater treatment plant (WWTP) effluent, concern is rising about impacts on human health and antibiotic resistance development. Furthermore, WWTP effluent may be released into waterways used as drinking water sources. The aim of this study was to analyze three antibiotics important to human health (sulfamethoxazole, ofloxacin, and trimethoprim) in soil and groundwater at a long-term wastewater reuse system that spray irrigates effluent. Soil samples were collected (i) at a site that had not received irrigation for 7 mo (approximate background concentrations), and then at the same site after (ii) one irrigation event and (iii) 10 wk of irrigation. Water samples were collected three times per year to capture seasonal variability. Sulfamethoxazole was typically at the highest concentrations in effluent (22 ± 3.7 mg L ^-1 ) with ofloxacin and trimethoprim at 2.2 ± 0.6 and 1.0 ± 0.02 mg L ^-1 , respectively. In the soil, ofloxacin had the highest background concentrations (650 ± 204 ng kg-1), whereas concentrations of sulfamethoxazole were highest after continuous effluent irrigation (730 ± 360 ng kg ^-1 ). Trimethoprim was only quantified in soil after 10 wk of effluent irrigation (190 ± 71 ng kg ^-1 ). Groundwater concentrations were typically <25 ng L ^-1 with high concentrations of 660 ± 20 and 67 ± 7.0 ng L ^-1 for sulfamethoxazole and ofloxacin, respectively. Given that antibiotics interacted with the soil profile and groundwater concentrations were frequently about 1000-fold lower than effluent, soil may be an adequate tertiary treatment for WWTP effluent leading to improved water quality and protection of human health.