Abstract
The Mekong Delta in Vietnam has seen a rapid development and intensification of aquaculture in the last decades, with a corresponding widespread use of antibiotics. This study provides information on current antibiotic use in freshwater aquaculture, as well as on resulting antibiotic concentrations in the aquatic environment of the Mekong Delta. Two major production steps, fish hatcheries and mature fish cultivation, were surveyed (50 fish farm interviews) for antibiotic use. Different water sources, including surface water, groundwater and piped water (164 water samples) were systematically screened for antibiotic residues. To better understand antibiotic fate under tropical conditions, the dissipation behavior of selected antibiotics in the aquatic environment was investigated for the first time in mesocosm experiments. None of the investigated antibiotics were detected in groundwater and piped water samples. Surface water, which is still often used for drinking and domestic purposes by local populations, contained median concentrations of 21 ng L-1 sulfamethoxazole (SMX), 4 ng L-1 sulfadiazine (SDZ), 17 ng L-1 trimethoprim (TRIM), and 12 ng L-1 enrofloxacin (ENRO). These concentrations were lower than the predicted no effect concentrations (PNECs) and minimum inhibitory concentrations (MICs), suggesting limited antibiotic-related risk to aquatic ecosystems in the monitored systems. The dissipation half-lives of the studied antibiotics ranged from <1 to 44 days, depending on the availability of sunlight and sediment. Among the studied antibiotics TRIM was the most persistent in water systems. TRIM was not susceptible to photodegradation, while the dissipation of ENRO and SDZ was influenced by photolysis. The recorded dissipation models gave good predictions of the occurrence and concentrations of TRIM, ENRO and SDZ in surface water. In summary, the currently measured concentrations of the investigated antibiotics are unlikely to cause immediate risks to the aquatic environment, yet the persistence of these antibiotics is of concern and might lead to chronic exposure of aquatic organisms as well as humans.
Highlights
Vietnam, followed by Indonesia, Bangladesh, Thailand, Myanmar and the Philippines, was the number one producer of aquaculture products in Southeast Asia in 2010
Local fish farmers’ knowledge of the properties or dosage of used antibiotics was not optimal; antibiotics have been used for prophylaxes, without worker protection and without exact knowledge about the required dosage
The questionnaires revealed that applications mainly consisted of sulfonamides, jointly with TRIM, tetracyclines, fluorquinolones (ENRO), and penicillins
Summary
Vietnam, followed by Indonesia, Bangladesh, Thailand, Myanmar and the Philippines, was the number one producer of aquaculture products in Southeast Asia in 2010. The lower Mekong Delta (Vietnam) contributed 57% of this output in 2011 [2]. The economic benefit of aquaculture production is affected by disease outbreaks caused by bacterial infection, viruses or parasites. Chemical and biological products, antibiotics, have been applied to aquaculture ponds to prevent and treat diseases and to promote growth. It was estimated that about 0.15 kg of medicine containing antibiotics was used for each ton of fish produced [3]. In the absence of treatment facilities, antibiotics are likely to reach the water system, causing water pollution and probably contributing to the development of resistant strains of bacteria (e.g., [5,6])
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