Abstract
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•Ciprofloxacin at up to 1 μg L−1 inhibits Raphidocelis subcapitata growth parameters.•Caffeine increases the growth inhibition EC50 by 6.6 times after 96h-exposure.•Longer exposure times lead to higher growth inhibition of Raphidocelis subcapitata.•Diverse endpoints and longer exposure times give more real ecotoxicological assays.
Ciprofloxacin (CIP) is an antimicrobial “pseudo-persistent” in aquatic ecosystems. Once dispersed in the water compartments, it can also affect the microalgae. Thus, the evaluation of its long-term ecotoxicological effects is necessary. CIP interactions with other pharmaceuticals are not well known. In this study, we investigated the toxic effects of CIP alone and combined with caffeine (CAF), using the modified Gompertz model parameters and the chlorophyll-a production of the microalga Raphidocelis subcapitata as endpoints, throughout a 16-day exposure assay. The exposure to CIP alone led to significant reductions of the growth rate and the cell density of the microalgae compared to control groups. The combination with CAF lowered the adverse effects of CIP to R. subcapitata. However, as the toxicity is dynamic, our results indicated that the toxic effects in respect to the studied endpoints changed throughout the exposure period, reinforcing the need for longer-term ecotoxicity assessments.