Effects of triclosan and triclocarban on the growth inhibition, cell viability, genotoxicity and multixenobiotic resistance responses of Tetrahymena thermophila

The information about adverse effects of emerging contaminants on aquatic protozoa is very scarce. The growth inhibition effect, cell viability, genotoxicity and multixenobiotic resistance (MXR) responses of two commonly used antimicrobial agents, triclosan (TCS) and triclocarban (TCC) to protozoan Tetrahymena the rmophila were investigated in this study. The results revealed that TCS and TCC can inhibit the growth of T. thermophila with 24 h EC50 values of 1063 and 295 mu g L-1, respectively. The impairment of plasma membrane was observed after 2 h exposure of TCS or TCC at the level of mg/L. Furthermore, it is noticeable that at environmentally relevant concentration (1.0 mu g L-1), both TCS and TCC can lead to statistically significant DNA damage in T. thermophila, while the inhibition of growth and change of cell viability cannot be observed. Our results firstly provide the evidence for genotoxic effects of TCS and TCC on the freshwater protozoan. Additionally, both TCS and TCC were found to inhibit the efflux transporter activities, with the inhibitory potencies of 39% and 40% (using verapamil as a model inhibitor), respectively. Particularly, TCC could significantly down-regulate the expression of MXR related gene Abcb15, which encodes the membrane efflux protein that acting as P-gp in T. the rmophila. The results raise the awareness of potential aquatic ecological and human health risks from the exposure of TCS and TCC, as they might potentiate the toxic effects by chemosensitizing with co-existing toxicants. (C) 2015 Elsevier Ltd. All rights reserved.