Comparing the Environmental Fate of Typical Antibiotics Sulfamethoxazole and Enrofloxacin in Aquaculture Using a Multi-media Environmental Fugacity Model

The antibiotics sulfamethoxazole and enrofloxacin are commonly used in aquaculture in China, but their fates within the culture environment of tilapia are unclear. Based on the "Guidelines for the use of fishery drugs" (NY 5071-2002) and the "Code for the use of enrofloxacin in aquaculture" (SC/T 1083-2007), the distributions of these two drugs within the tilapia culture environment were studied through field culture experiments. The multi-medium environmental fugacity model was used to simulate the behavior and fate of the drugs. The predicted proportional distributions of sulfamethoxazole in the aquaculture water, fish body and sediment were 92.10%, 7.28% and 0.60%, respectively, and for enrofloxacin the proportions were 64.10%, 35.50% and 0.44%, respectively. While the actual measured proportional distributions of sulfamethoxazole in the culture water and fish were 74.87% and 2.66% (muscle 1.03%, liver 1.10%, intestinal content 0.53%), respectively. For enrofloxacin, the fish body accounted for 36.29% (muscle 33.35%, liver 1.62%, intestinal content 1.32%) of the distribution, but enrofloxacin was not detected in either the culture water or sediment samples. The times for sulfamethoxazole levels to decrease to their initial values in the culture water, muscle, liver and intestinal tract(2.5±0.9) ng·mL^-1 in water, (2.7±0.1) ng·g^-1 in muscle, (37.0±9.3) ng·g^-1 in liver, and (21.5±5.4) ng·g^-1 in intestine were 32.5, 36.0, 13.1 and 20.4 d respectively. For enrofloxacin, the corresponding elimination times were 5.7 d and 10.3 d for liver and intestine, respectivelyliver (4.5±0.3) ng·g^-1, intestinal tract (31.7±2.7) ng·g^-1, but complete elimination did not occur in muscleinitial value of muscle (8.1±2.0) ng·g^-1; residual concentration, (55.7±4.9) ng·g^-1. It is suggested that the withdrawal periods for sulfamethoxazole and enrofloxacin should not be less than 36 d and 20 d, respectively. These data will be valuable for the protection of the ecological environment of fishery and to ensure the quality and safety of tilapia aquacultural products.