Effects of enrofloxacin, ciprofloxacin, and trimethoprim on two generations of Daphnia magna

•Transgenerational toxicity of enrofloxacin in Daphnia magna.•Acclimatisation to trimethoprim toxicity in the second generation of Daphnia magna.•High reproductive toxicity of enrofloxacin in Daphnia magna.•Low toxicity ratio (acute/chronic) of fluoroquinolones.

Multigenerational tests on Daphnia magna were performed exposing two subsequent generation to enrofloxacin (EFX) and its metabolite ciprofloxacin (CPX), and to trimethoprim (TMP). Mortality rate of 100% and 50% was detected in F0 at concentrations of ≥13 mg L−1 (EFX) and 50 mg L−1 (TMP), respectively. In F1 with respect to F0, both for growth and reproduction, a worsening trend of the response with EFX, a similar response with CPX and an attenuating trend with TMP was observed. Furthermore, the lowest EC20 for reproduction inhibition (1.3 mg L−1) was calculated for F1 exposed to EFX. However, other experimentations, longer and more complex, are necessary in order to confirm that EFX is more hazardous to daphnids than CPX and TMP. EC50 measured for the three assayed antibacterials were in the 6.5–37 mg L−1 range therefore environmental unrealistic, except in case of exceptional contaminations that may occur in relation to poorly controlled wastewaters from pharmaceutical factories or excessive use of prophylactic treatments in aquaculture.