Acute Toxicity, Bioaccumulation, and Bioreduction of Two Antibiotics, Norfloxacin and Ofloxacin, in the Snail Bellamya aeruginosa

Fluoroquinolones (FQs) present in water environments pose threats to aquatic organisms. The concentration of FQs adsorbed onto sediments is generally higher than that in water. Here, we studied the toxicities of two FQ antibiotics, norfloxacin (NOR) and ofloxacin (OFL), on the snail Bellamya aeruginosa, an adaptable benthic animal. For this, we performed acute toxicity experiments on young snails and sub-chronic exposure experiments on adult snails by exposure to the FQs for 1–28 days. The 96 h median effective concentrations showed that NOR toxicity was higher than OFL toxicity, although both NOR and OFL were low-toxicity substances (EC50 > 100 mg L−1). Four concentrations were used in the sub-chronic exposure experiments. Results of the measurement of bioconcentration factors (BCF) showed that OFL accumulation was higher than NOR accumulation in snail tissues. During the depuration period (28–49 days), at low concentrations (2 and 20 μg L−1), both FQs required at least 7 days to reach the maximum residue limit (50 μg kg−1). Conversely, at high concentrations (200 and 2000 μg L−1), 14 days (NOR) and 21 days (OFL) were required. Our results could facilitate management of the environmental risks of antibiotics and conservation of aquatic animals.