Mixture toxicity of zinc oxide nanoparticle and chemicals with different mode of action upon Vibrio fischeri

Abstract Background: Zinc oxide nanoparticle ( n ZnO) and chemicals with different mode of action (MOA, i.e., narcotic and reactive) were frequently detected in the Yangtze River. Organisms are typically exposed to mixtures of n ZnO and other chemicals rather than individual n ZnO. Toxicity of n ZnO is caused by the dissolution of Zn 2+ , which has been proved in the field of single toxicity. However, it is still unclear whether the released Zn 2+ plays a critical role in the n ZnO toxicity of n ZnO-chemicals mixtures. In the present study, the binary mixture toxicity of n ZnO/Zn 2+ and chemicals with different MOA was investigated in acute (15 min) and chronic (12 h) toxicity test upon Vibrio fischeri ( V. fischeri ). The joint effects of n ZnO and tested chemicals were explored. Moreover, two classic models, concentration addition (CA) and independent action (IA) were applied to predict the toxicity of mixtures. Results: The difference of toxicity unit (TU) values between the mixtures of Zn 2+ -chemicals with those of n ZnO-chemicals was not significant ( P > 0.05), not only in acute toxicity test but also in chronic toxicity test. The antagonistic or additive effects for n ZnO-chemicals can be observed in most mixtures, with the TU values ranging from 0.75-1.77 and 0.47-2.45 in acute toxicity test and chronic test, respectively. We also observed that the prediction accuracy of CA and IA models was not very well in the mixtures where the difference between the toxicity ratios of the components was small (less than about 10), with the mean absolute percentage error (MAPE) values ranging from 0.14-0.67 for CA model and 0.17-0.51 for IA model, respectively. Conclusion: We found that the dissolved Zn 2+ mainly accounted for the n ZnO toxicity in the mixtures of n ZnO-chemicals, and the joint effects of these mixtures were mostly antagonism and additivity. CA and IA models were unsuitable for predicting the mixture toxicity of n ZnO-chemicals at their equitoxic ratios.