Chronic toxicity of the veterinary antibiotic florfenicol to Daphnia magna assessed at two temperatures

• Florfenicol (FLO) effect to freshwater organisms was investigated at 20 and 25 °C.
• FLO caused chronic effects on Daphnia magna with higher toxicity at 25 °C.
• FLO decreased the somatic growth and the reproductive output of D. magna.
• FLO also decreased the population growth rate.

The hypothesis that temperature variation is able to modify the chronic toxicity of the antibiotic florfenicol (FLO) to Daphnia magna was tested in the present study. Twenty-one day laboratory bioassays were carried out at 20 and 25 °C. FLO concentrations and its potential decay during the assays were checked by spectrophotometry. At 20 °C, FLO significantly reduced the D. magna somatic growth (≥1.6 mg/L) and impaired its reproduction (EC20 = 6.9 mg/L; EC50 = 7.6 mg/L), with the population growth rate becoming negative at 12.6 mg/L. At 25 °C, the EC values were lower (1.7 and 1.9 mg/L, respectively) than at 20 °C, as well as the lowest exposure concentration causing a negative population growth rate (3.1 mg/L). These results clearly indicate that temperature raise from 20 to 25 °C was able to modify the FLO toxicity. Therefore, more studies on the combined effects of temperature changes and environmental contaminants are needed to improve the basis for ecological risk assessment, environmental and human safety.