Study On The Combined Toxicity Interaction Transfer And Mechanism Of Two Typical Pesticides On Chlorella Pyrenoidosa

Herbicide and pesticide are the two most widely used pesticides in agricultural production,and most of them are water-soluble.Every year,water environmental safety problems caused by pesticide residues entering the water body with runoff are common.In addition,new compound pesticides have become a hot research field in pesticide application.Studying the combined toxicity interaction（antagonism or synergism）of different pesticides with different concentration ratios is conducive to achieving the purpose of"reducing application and increasing efficiency".Therefore,two herbicides,diquat（DIQ）and cyanazine（CYA）,and three pesticides,dipterex（DIP）,propoxur（PRO）and oxamyl（OXA）,were taken as the research objects,and Chlorella pyrenoidosa was taken as the indicator organism.The dynamic changes of growth inhibition effects of C.pyrenoidosa at five different exposure time（12,24,48,72 and 96 h）in the whole exposure concentration gradient range from low to high were observed and analyzed by the time-dependent microplate toxicity analysis method（t-MTA）.The toxic joint action between or among simple and complex mixture components was analyzed by concentration addition（CA）model,extended isobologram method and deviation from CA（d CA）model,and the key components leading the interaction intensity and the transmission of the interaction were revealed.By studying the effects of pesticides and their mixtures on various physiological and biochemical indexes such as chlorophyll pigment content,protein content and dissolution,superoxide dismutase（SOD）activity and malondialdehyde（MDA）content of C.pyrenoidosa,and the changes of algae cell morphology before and after the exposure to pollutants,the adverse outcome of C.pyrenoidosa under pollutant stress was analyzed by the adverse outcome path（AOP）way.The research results are as follows:（1）The single toxicity of herbicides and pesticides to C.pyrenoidosa is concentration-dependent and time-dependent.Compared with pesticides,herbicides have a more obvious time-dependent relationship,and both pesticides have strong long-term toxicity.Among them,the toxicity of herbicides to C.pyrenoidosa is 1～2 orders of magnitude greater than that of pesticides.Taking p EC₅₀as the toxicity index,the toxicity order of the five pesticides at 96 h is CYA（5.73）>DIQ（5.21）>OXA（4.47）>PRO（4.35）>DIP（3.45）.（2）The toxicity of binary and partial ternary mixture systems of two kinds of pesticides is concentration-ratio dependent,that is to say,the toxicity of the mixture system increases with the increase of the concentration ratio of the more toxic components in the system.The toxicity of binary and ternary mixture systems is time-dependent,but the change rate of joint toxicity with time is different.The joint toxicity of quaternary and quinary mixtures is also time-dependent,but some systems have no obvious concentration-ratio dependence.（3）The main types of toxicity interaction within the mixtures of two kinds of pesticides are antagonism and synergism,and the interaction intensity of each mixture system increases with the extension of exposure time.The interaction type between two herbicides is mainly synergistic,and the interaction type among three pesticides is mainly antagonistic.The interaction between herbicide CYA and three pesticides is mainly antagonistic,and it may be the key component of the mixture system,and its concentration ratio determines the antagonism intensity of the system.The interaction type between herbicide DIQ and three pesticides is mainly synergistic,which may be the key component of the related system.（4）If all the binary mixture subsystems contained in the ternary mixture systems show a certain interaction type,then this interaction type will be transferred from the binary mixture systems to the ternary ones.If the binary mixture subsystems contained in the ternary mixture system have different interaction types and both interactions are not dominant,a"neutralization"result will be produced,that is,an additive effect will be shown.The interaction between components of a complex mixture system is determined by the interaction of the simpler mixture system it contains,that is,from simple to complex mixture,the interaction is transitive.（5）The interaction type of mixture system is related to the concentration ratio among its components,and a key component in the binary mixture system still continues its leading role in the ternary ones.In the more complex quaternary and quinary mixture systems,the appearance of key components is still the key factor to express the corresponding interaction types.The interaction of mixture rays in a simple mixture is more simple than that in a complex mixture,that is,different rays in a multicomponent mixture are more likely to show different interaction types with the change of concentration distribution among components,and with the"neutralization"between different interaction types,a more complex mixture is more likely to show additive effect.（6）Toxicity mechanism of pesticides and their mixtures to C.pyrenoidosa:firstly,excessive accumulation of peroxides in green algae cells under pesticide stress,and the stress resistance decreased.On the one hand,a large number of peroxides inhibit the synthesis of chlorophyll in algae cells,destroy the physiological function of chlorophyll and then affect the synthesis of protein and enzymes,and finally affect or destroy the cell structure;on the other hand,it causes lipid peroxidation in cell membrane system,destroys cell and organelle membrane system,causes macromolecular leakage,and finally shows algae apoptosis.Figure[71]table[40]reference[91]...