Use, fate and ecological risks of antibiotics applied in tilapia cage farming in Thailand

• First study assessing the risks of antibiotics applied in freshwater tilapia cages.
• Ten antibiotics were reported to be used by tilapia cage farmers in two Thai rivers.
• Peak oxytetracycline and enrofloxacin concentrations were in the order of μg/L.
• Antibiotic concentrations in river sediments next to cages were up to several mg/kg.
• Antibiotics are not posing a short-term risk for pelagic aquatic organisms.

The use, environmental fate and ecological risks of antibiotics applied in tilapia cage farming were investigated in the Tha Chin and Mun rivers in Thailand. Information on antibiotic use was collected through interviewing 29 farmers, and the concentrations of the most commonly used antibiotics, oxytetracycline (OTC) and enrofloxacin (ENR), were monitored in river water and sediment samples. Moreover, we assessed the toxicity of OTC and ENR on tropical freshwater invertebrates and performed a risk assessment for aquatic ecosystems. All interviewed tilapia farmers reported to routinely use antibiotics. Peak water concentrations for OTC and ENR were 49 and 1.6 μg/L, respectively. Antibiotics were most frequently detected in sediments with concentrations up to 6908 μg/kg d.w. for OTC, and 2339 μg/kg d.w. for ENR. The results of this study indicate insignificant short-term risks for primary producers and invertebrates, but suggest that the studied aquaculture farms constitute an important source of antibiotic pollution.

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