| The invention of pesticides has made outstanding contributions to the development of modern agriculture,but it has also brought serious water environment pollution problems,which is threatening living of the organisms,and even human’s health.It is reported that some pesticide metabolites are even more toxic than the pesticide itself.In recent years,the outbreak of COVID-19 has led to a sharp increase in the use of disinfectants,but the excessive use of disinfectants is inevitably accompanied by the production of a large number of disinfection byproducts(DBPs),bringing many safety risks to human health and the environment.Pesticides,their metabolites and disinfection byproducts,as pollutants with high residual amount in the water,naturally have the possibility of coexistence,resulting in the formation of complex mixed pollutants,with greater environmental risks.Therefore,it is of great practical environmental significance to study the toxicity of pesticides and their metabolites combined with disinfection by-products.Therefore,one commonly used pesticide: dipterex(DIP)and its metabolites:trichloroethanol(TRI),dichloroacetamide(DCAM)and four nitrogenous disinfection by-products(N-DBPs): bromoacetonitrile(BAN),dibromoacetonitrile(DBAN),dichloroacetamide(DCAM)and N-nitrosodimethylamine(NDMA)were used as target contaminants,and a fresh water photobaterium Vibrio-qinghaiensis sp.-Q67(Q67)as the test organism.The binary and multi-mixture systems of DIP and its metabolites with N-DBPs were designed by direct homogeneous ray(Equ Ray)and uniform design ray(UD-Ray)methods,respectively.The toxicity characteristics of DIP and its metabolites in single and multiple mixtures with N-DBPs were determined at different exposure time(0.25,2,4,8 and 12 h)by using the time-dependent toxicity microplate analysis(t-MTA).The toxic interactions were qualitatively analyzed and quantitatively characterized by combining two models of concentration addition(CA)and deviation from CA model(d CA).The effects of the six contaminants and their mixtures on the structure and morphology of Q67 cells were observed by scanning electron microscopy,and the protein leakage from Q67 cells was determined by coomassie brilliant blue method.Finally,the experimental results of cell membrane permeability were obtained by measuring the changes of conductivity parameters before and after the radiographic effects of the six drugs and their multi-representative mixtures.The main conclusions obtained from the study are as follows:(1)All six target pollutants showed good dose-effect relationships for toxicity to Q67,and all had strong acute and long-term toxicity.The toxicity order of DIP and its metabolites and the four N-DBPs varied with time.DIP metabolite TRI had higher acute toxicity than the parent compound DIP,and DIP had higher long-term toxicity than its metabolites DCAM and TRI,while the long-term toxicity of all four N-DBPs to Q67 was greater than their acute toxicity.(2)The toxicity characteristics of the binary and ternary mixtures of DIP and its metabolites(DCAM,TRI)were dependent on the individual components,with each mixture of rays showing significant short-term and long-term toxicity to Q67,and time-dependent and concentration-ratio-dependent toxicity.The types of toxic effects of the binary and ternary mixtures were mainly weak antagonism and summation,with some rays showing weak synergism.For mixtures showing antagonistic or synergistic effects,the strength of the interaction was influenced by the combination of exposure time,components and their concentration ratios,i.e.the antagonistic or synergistic strength varied with exposure time,components and component concentration ratios.In the binary mixture,the DIP-TRI-R5 rays showed the most pronounced antagonism at 12 h exposure time,with a maximum antagonistic intensity of 0.22.In the ternary mixture,the DIP-DCAM-TRI-R2 rays showed the most pronounced antagonism at 4 h exposure time,with a maximum antagonistic intensity of 0.22.(3)The toxicity time characteristics of the binary,ternary and quaternary mixtures of the four N-DBPs were not identical,but all of them had strong acute and long-term toxicity.The toxic interactions of the binary,ternary and quaternary mixtures of the four N-DBPs were all concentrated in the middle and high concentration regions,and the intensity of the interactions changed with the increasing of exposure time exhibiting time-dependency.The strongest synergistic effect of the binary mixture was up to 0.25 and the strongest antagonistic effect was up to 0.49.The strongest synergistic effect of the ternary mixture was 0.28 and the strongest antagonistic effect was up to 0.18,while the strongest synergistic intensity of the quaternary mixture was 0.23.(4)The toxicity of binary and hexametric mixtures of DIP and its metabolites with N-DBPs was dependent on the individual components,and all had significant acute and long-term toxicity.The time-dependent toxicity of some of the binary mixtures was not significant.The toxicity of the binary and hexametric mixtures of DIP and its metabolites with N-DBPs varied with the concentration ratio of the components at the same time,and the concentration ratio-dependent toxicity was evident.In addition,the synergistic and antagonistic effects between DIP and its metabolites and the binary mixtures of the four N-DBPs were evident,with the synergistic effects occurring mainly during short-term exposure times and the toxic interactions between the binary mixtures being mostly antagonistic during long-term exposure times.The synergistic effects of the hexamers on Q67 were mainly concentrated in the middle and high concentration regions,and the strength of the synergistic effects changed from strong to weak and then to strong as the exposure time increased.The synergistic intensity of the seven rays of the hexamer mixture varied at the same exposure time,with the strongest synergistic effect of ray U3 at 12 h,with a maximum synergistic intensity of 0.70 and a concentration-dependent synergistic effect.(5)DIP and its metabolites,both individually and in mixtures with N-DBPs,damaged the normal cell structure of Q67.Q67 cells showed a rupture of the external shape,the boundaries between cell structures became unclear,intercellular adhesions occurred,some of the bacteriophage cells fused with each other,the cell membrane became unsmooth and could not maintain its normal shape.The drugs also caused the efflux of soluble protein macromolecules,and the soluble protein macromolecule content in the culture fluid increased compared to the control group. |
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