Characteristics And Mechanism Of Joint Toxicity Of Two Typical Pesticides On Chlorella Pyrenoidosa

Carbamates and organophosphorus pesticides are widely used two kinds of pesticides in agriculture,so they probably are accompanied by runoff into the water body and cause water pollution.Nowadays,many studies published have found that two kinds of pesticides are of strong toxic effects.So,five carbamate pesticides:bayon?BAY?,metomyl?MET?,pirimicarb?PIR?,aldicarb?ALD?,carbofuron?CAR?and three organophosphorus pesticides:acephate?ACE?,trichlorfon?TRI?,glyphosate?GLY?were selected as research substances,and Chlorella pyrenoidosa?C.pyrenoidosa?was used as test organism.Time-dependent microplate toxicity analysis?t-MTA?was used to determine the growth inhibition data of carbamate pesticides and their multiple mixtures,organophosphate pesticides and their multicomponent mixtures and octagonal mixtures of the two types pesticide to C.pyrenoidosa in different exposure times?12,24,48,72 and 96 h?.The concentration addition?CA?model was used to analyze the toxic interactions within multiple mixtures,and the toxicity mechanism was investigated by analyzing the effects of different pesticides and their mixtures on the chlorophyll content,protein content,superoxide dismutase?SOD?activity and lipid peroxidation?MDA?content as well as the changes in the structure of C.pyrenoidosa in different exposure times.The results are as follows:?1?Toxicity of eight pesticides on C.pyrenoidosa has significant time-con centration-effect characteristics.PIR promotes the growth of C.pyrenoidosa at l ow and medium concentrations,and presents a non-monotonic J-type concentrat ion-response curve?CRC?characteristic.The remaining seven pesticides have to xic inhibition effects,and the CRCs present classic S-types.The eight pesticide s have different levels of toxicity,which change with prolonged exposure.Taki ng the negative logarithm of medium effect concentration(pEC₅₀)value as toxi city index,toxicity order of eight pesticides in 96 h is:CAR(pEC₅₀=3.43)>BA Y(pEC₅₀=2.76)>GLY(pEC₅₀=2.595)>PIR(pEC₅₀=2.12)>MET(pEC₅₀=2.11)>ALD(pE C₅₀=1.89)>TRI(pEC₅₀=1.62)>ACE(pEC₅₀=0.226).?2?Five carbamate pesticide mixtures,three organophosphorus pesticide mixtures and Octagonal mixtures have obvious time-dependent toxicity characteristics to C.pyrenoidosa in different exposure time.And there is a significant difference in CRC in 96 h.Changes of mixture compositions will cause toxic irritation in low-concentration areas.?3?Interactions within carbamate pesticide mixtures,organophosphorus pesticide mixtures,and octagonal mixtures are affected by factors such as exposure time,component concentration ratios,and concentration regions,which,for example in 96h,not only affects the toxic effect of the mixture,but also the interaction within the mixture.That is,when the concentration ratio of most toxic component is negatively linear with pEC₅₀,and the concentration ratios of other components are positively linear or without relationship with pEC₅₀,interaction of the mixture is basically an antagonistic effect.While the concentration ratio of most toxic component is positively linear with pEC₅₀,and the concentration ratios of other components is negatively linear or without relationship with pEC₅₀,interaction of the mixture is basically synergistic.?4?Under the inhibitory concentrations of five carbamate pesticides and their mixtures,and three organophosphorus pesticides and their mixtures,chlorophyll,protein and SOD activity in algal cells decrease continuously and the MDA content increase with time lengthening.The algal cell structure is destroyed with the cell structure being broken and deform,the chloroplast being destroyed and the matrix being??darkened.The chlorophyll,protein,and SOD activities in algal cells were continuously increased compared to the blank control under the effects of the stimulus concentration.The MDA content reduced,the algal cell structure was basically complete,and the cell wall becomes thin and convex,but the chloroplast structure is complete,the matrix becomes green,and the nucleus the structure of the protein core is unbroken and clearly visible.?5?Under the inhibitory concentration of three organophosphorus pesticides and their mixtures,the chlorophyll,protein content,and SOD enzyme activity of algal cells reduce,some cells even die.The reduction rates of chlorophyll and protein content,especially protein content,are significantly higher than the toxicity inhibition increase rate.The reason may be the strong acute toxicity of organophosphorus pesticides,which severely destroys the structure of chlorophyll and proteins,and eventually leads to irreversible phenomena.?6?Under the inhibitory concentration of the eight-element mixture,the chlorophyll content,protein content and SOD enzyme activity in the algae cells will continue to decrease,and the MDA content will increase.It shows that the toxic effect of the eight-element mixture is the same as that of a single pesticide,also by destroying the cell structure.?7?Toxicity mechanisms of five carbamate pesticides,three organophosphorus pesticides and their mixtures on C.pyrenoidosa are:first,the pollutants pass through the cell membrane,accumulate in the organism,and then the chlorophyll,protein and Enzyme activity changes,which in turn inhibit or promote the growth of cell,or cause cell deformation,and finally show toxicity inhibition and promotion effects.