The Fate of Three Human Antibiotics in Agroecosystems Due to the Reuse of Wastewater Treatment Plant Effluent.

With diminishing water supplies, the reuse of wastewater treatment plant (WWTP) effluent to irrigate agricultural lands is occurring more frequently. Emerging contaminants, such as antibiotics, are typically found in the effluent that is released into the environment due to limited removal during WWTP processes. In particular, concern has arisen about the environmental fate of antibiotics and the possible impacts on microbial communities, especially antibiotic resistance in soil bacteria. This study examined the fate of three human antibiotic compounds in the environment when WWTP effluent was spray irrigated year round on agricultural land. Sulfamethoxazole, trimethoprim, and ofloxacin were quantified in WWTP influent and effluent, soil, groundwater, and wheat plants (Triticum aestivum). The three antibiotic compounds were typically present in WWTP influent and effluent throughout the year with concentrations varying by season and population density (2 - 22,000 ng/L). These antibiotic compounds were also found in groundwater throughout the year with concentrations that ranged from 0.5 to 300 ng/L. Typically, sulfamethoxazole was the antibiotic compound present in water samples at the highest frequency and concentration. In wheat plants, only ofloxacin and sulfamethoxazole were found in the grain at concentrations of 2,300 ± 900 ng/kg and 640 ± 340 ng/kg, respectively. Antibiotic concentrations were also detected and quantified in soil down to a depth of approximately 80 cm with ofloxacin appearing to be the most persistent compound (ng/kg range). Overall, these findings indicate that spray irrigation of agricultural lands with WWTP effluent leads to the occurrence of antibiotic compounds in various compartments of the environment. The presence of these compounds could have unknown ecological impacts, such as alterations in microbial communities and antibiotic resistance in soil bacteria. Additional research is necessary to determine the full implications to environmental health when WWTP effluent is reused for the purpose of irrigation.