Predicting the time-dependent toxicities of three triazine herbicide mixtures to V. qinghaiensis sp. Q67 using the extended concentration addition model

Abstract

The concentration addition (CA) model is a common model for the evaluation and prediction of mixture toxicity and has been widely used in many mixture systems such as drug combination and pesticide mixtures. However, it is necessary to extend the CA so that it is applicable in the mixture systems including components with different effects in different times. In this paper, three triazine herbicides, metribuzin (MET), simetryn (SIM) and hexazinone (HEX), which have different characteristics of the time-dependent toxicity, were selected as mixture components and their binary mixtures were designed by using the direct equipartition ray design (EquRay). Taking V. qinghaiensis sp.-Q67 as test organism and 96-well microplate as exposure experiment carrier, the luminescence inhibition toxicities of three triazine herbicides and their binary mixtures were determined at six different time points (0.25, 2, 4, 8, 12 and 16 h). The fluctuation tendency of the luminescence inhibition toxicity varying with time was analyzed. The results show that the inhibition toxicities of three triazine herbicides to V. qinghaiensis sp.-Q67 have different characteristics of the time-dependent toxicity, i.e., the toxicity of MET apparently increases over time, while that of SIM is basically a constant in the range of testing time, but that of HEX first increases with time at the beginning stage and then is basically unchanged. Also, the toxicities of the binary mixtures consisting of three herbicides depend on not only the composition of the mixtures but also the concentration ratio of various components. The toxicity of binary mixture consisting of MET and HEX gradually increases over time, and that of binary MET-SIM mixture at first decreases and then slowly increases, while the toxicity change is not significant in the SIM-HEX mixture system. Moreover, all the toxicities of binary mixtures can be effectively predicted by the CA model which had been extended by regarding the concentration of no-effect component as infinity, being additive, not synergistic or antagonistic. © 2014 Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences.