Comparative Evaluation on Combined Ecotoxic Effects of Nitrofurazone and NH 4 CI Using Two Ciliated Protists as Model Organisms: Population Dynamics and Growth Rates

Ecotoxic effects of antibiotics or ammonium have been confirmed independently in aquatic animals, but few studies have investigated their combined effects. In aquaculture ecosystems, these pollutants frequently coexist, and often in high concentrations. In this study, the combined effects of antibiotic nitrofurazone and NH4Cl on the population dynamics and growth rates of two species of ciliated protists, Euplotes vannus and Pseudokeronopsis rubra , were investigated. Profiles of the dose-responses were visualized, and interactions between the two pollutants were quantified by the response surface method (RSM). Results showed that 1) the dynamics of the population growth differed significantly between the testd ciliates and varied with the concentrations of the pollutants; 2) the relative growth rate (RGR) of both ciliates decreased significantly with increased pollutant concentrations, while the difference in RGR between the two ciliates was not significant; 3) RSM analysis demonstrated an additive effect of nitrofurazone and NH4Cl on the RGR in both ciliates. In brief, ecotoxic effects can be caused by nitrofurazone and ammonium independently on the two test ciliates, and such effects can be strengthened when they present at the same time. These findings offer a valuable reference for evaluating combined ecotoxic effects caused by multiple pollutants in aquaculture ecosystems.