Chemical fate and partitioning behavior of antibiotics in the aquatic environment: a review

Antibiotics in the aquatic environment is a major problem because of the emergence of antibiotic resistance.The long‐term ecological impact on the aquatic environment is unknown. Many sources allow entry of antibiotics intothe environment, including wastewater‐treatment plants (WWTPs), agricultural runoff, hospital effluent, and landfill leachate.Concentrations of antibiotics in the aquatic environment vary significantly; studies have shown fluoroquinolones, tetracycline,macrolides, sulfonamides, and penicillins to reach 2900, 1500, 9700, 21 400, and 1600 ng L–1 in wastewater effluent samples,respectively. However, concentrations are highly variable between different countries and depend on several factors includingseasonal variation, prescription, and WWTP operating procedures. Likewise, the reported concentrations that causeenvironmental effects vary greatly between antibiotics, even within the same class; however, this predicted concentration forthe antibiotics considered was frequently <1000 ngL–1, indicating that when discharged into the environment along withtreated effluent, these antibiotics have a potentially detrimental effect on the environment. Antibiotics are generally quitehydrophilic in nature; however, they can ionize in the aquatic environment to form charged structures, such as cations,zwitterions, and anions. Certain classes, particularly fluoroquinolones and tetracyclines, can adsorb onto solid matrices,including soils, sediment, and sludge, making it difficult to fully understand their chemical fate in the aquatic environment.The adsorption coefficient (Kd) varies between different classes of antibiotics, with tetracyclines and fluoroquinolonesshowing the highest Kd values. The Kd values for fluoroquinolones, tetracyclines, macrolides, and sulfonamides have beenreported as 54 600, 7600, 130, and 1.37 L kg–1, respectively. Factors such as pH of the environment, solid matrix (sediment/soil sludge), and ionic strength can influence the Kd; therefore, several values exist in literature for the same compound.