Single chemical and mixture effects of three veterinary antibiotics on freshwater invertebrate test species
摘要
The widespread use of veterinary pharmaceuticals in animal husbandry has raised growing concerns about detrimental effects to non-target organisms. In this study we examined the acute and chronic effects of three veterinary antibiotics (erythromycin, tylosin and sulfamethazine) in single, binary and tertiary mixtures to two species of cladocerans, Daphnia magna and Ceriodaphnia dubia, and to larvae of the midge, Chironomus dilutus. Acute median lethal concentrations (48-h LC50) ranged from 87 mg/L (sulfamethazine) to 566 mg/L (tylosin) for D. magna and 77 mg/L (sulfamethazine) to 444 mg/L (tylosin) for C. dubia. For the midge, 96-h LC50 values for each of the chemicals alone was 256 mg/L for erythromycin and > 1000 mg/L for tylosin and sulfamethazine. The 10-day EC50 values for D. magna reproduction ranged from 5.7 mg/L (sulfamethazine) to 193 mg/L (tylosin), while for C. dubia these values ranged from 2.4 mg/L (sulfamethazine) to 321 mg/L (tylosin). Effects on growth and survival of C. dilutus in 10-day bioassays were only observed for erythromycin and sulfamethazine, with EC50 values all greater than 200 mg/L. No chronic effects were observed for midges exposed to tylosin at concentrations up to 500 mg/L. Combining the antibiotics in mixture generally reduced their acute and chronic LC and EC50 values. The lowest EC50 value generated was 1 mg/L sulfamethazine for C. dubia reproduction in a 7-day bioassay with sulfamethazine and tylosin in combination. Still, toxic unit calculations indicated predominantly additive interactions between the three antibiotics. Overall, the effects concentrations generated were well above reported water concentrations, indicating these chemicals may present a low level of risk to the aquatic organisms assessed in this study.