Mixture Toxicities of Three Pesticides Having Different Time-Toxicity Profiles

In the environment,chemical pollutants always exist as mixtures.To evaluate mixture toxicity,we should ex-amine the concentration ratios and the concentration levels of mixture components as well as the interactive time between the components and testing organism.Selecting three pesticides,metribuzin(MET),dodine(DOD)and ri-domil(RID),as mixture components,Vibrio qinghaiensis sp.-Q67 as testing organism,and 96-well microplate as exposure experiment carrier,the luminescence inhibition toxicities of the pesticides and their binary mixtures at six exposure time points(0.25,2,4,8,12,and 16 h)were determined.The results showed that the three pesticides have different time-toxicity profiles.The toxicity of MET increases over time,and those of DOD and RID show a slight decrease or increase in the first 4 h,respectively,and then remain unchanged to 16 h.The toxicities of the binary mixtures consisting of the three pesticides depend on not only the mixture composition but also the exposure time.The time-toxicity profiles of all rays in MET-DOD mixture system are U-shaped curves,those in MET-RID system are basically monotonically increased and those in DOD-RID system are basically monotonically decreased.How-ever,our findings indicate that for the test substances,mixture toxicity can be predicted by the extended concentra-tion addition model.