Differences In Acute Toxicity And Mechanism Of Different Formulation Of Pyraclostrobin To Zebrafish(Danio Rerio)

As a result of the diversity of field environments,agents exhibit significantly differentiated behaviors in foliar and aqueous environments after application.Especially in the aqueous environment,the active ingredients undergo a series of state and dynamic behavioral changes such as crystallization,sedimentation and degradation（light,water,microorganisms）,and the differences in the behavior of the active ingredients of different pesticide dosage forms in the aqueous environment are likely to lead to differences in the actual toxicity risk to aquatic organisms with different habits.For high-risk pesticides with excellent performance in rice pests and diseases,the assessment of their toxicity risk mainly focuses on acute/chronic toxicity effects,targets of action,and mechanisms of toxicity,etc.About their dynamic change patterns in the water field,the mechanisms of toxicity differences to aquatic organisms,and the key parameters regulating toxicity are still unclear.In this study,we used pyraclostrobin as a typical model pesticide and zebrafish as a model organism to study the behavioral differences of different dosage forms such as emulsifiers,suspensions and microencapsulated suspensions in water bodies and the acute toxicity differences to aquatic organisms,and analyzed the correlation mechanisms between them with correlation models,so as to provide a basis for the development of efficient and low-toxicity pesticide dosage forms suitable for use in paddy fields.The main results are as follows.1.Three emulsifiable formulations of pyraclostrobin were prepared using xylene,methyl oleate and ethylene glycol diacetate as solvents,and the average particle size of the dilutions was 1.8μm.three different particle sizes of pyraclostrobin suspensions with average particle sizes of 5μm,3μm and 1μm were prepared by varying the grinding time.Two microencapsulated suspensions with the same particle size and release rate were prepared by interfacial polymerization,and the density of the encapsulated spheres was 1.19 kg/m³ and 1.02 kg/m³,respectively.The virulence and control efficacy of the above pyraclostrobin samples were determined by mycelial growth rate method and inoculation test in pots,and the EC₅₀ values ranged from 0.0036-0.021 mg/L,and the control efficacy was above 67.58%.2.The acute toxicity of the eight pyraclostrobin samples against zebra mussel under conventional test conditions was EC-MO>EC-Xylene>EC-EGDA>SC-5μm>SC-3μm>SC-1μm>CS-Small>CS-Large.The LC₅₀ value of EC-MO was 38.5μg/L and that of CS-Large was 698.3μg/L,with a difference of 18.14 times.It can be seen that the toxicity of pyraclostrobin was much less when it was encapsulated by the capsule in water and exposed in the indirect state than when it was exposed in the emulsion droplet or crystal state and directly.The correlation analysis revealed that the amount of enrichment of the agent on gill tissues and inhibition of changes in gill cell activity were important reasons for the differences in toxicity between formulations.3.All eight pyraclostrobin samples were significant differences in the distribution in water with the sedimentation rate of SC-5μm>EC-EGDA>CS-Large>SC-3μm>SC-1μm>CS-Small>EC-Xylene>EC-MO.with the increase of solvent hydrophilicity and density of emulsion formulations,the particle size and density of suspensions and microcapsule suspensions increase,the active ingredient settles faster in water,thus significantly reducing the effective dose suspended in water.Among them,the remaining active ingredient content of SC-5μm in the upper water layer was only19.00%,the active ingredient content of EC-EGDA in each water layer was 30.00%-39.33%of the initial one,and the remaining active ingredient content of CS-Large was32.00%-35.67%.4.The different temporal and spatial distribution of active ingredients in water for different formulations affects the chance of contact between the agent and zebrafish,which in turn produces spatial and temporal toxicity effects.For example,zebrafish mortality in the upper water layer of EC-EGDA,SC-5μm and CS-Large samples was2-2.5 times higher than in the upper water layer,and their corresponding BCF values ranged from 1.70-2.30 times.With increasing resting time,all seven drugs decreased to different degrees,except for the light capsule sample.Therefore,the reduction of toxicity risk can be achieved by reducing the chance of contact with zebrafish and reducing the enrichment of pyraclostrobin in zebrafish.In summary,in addition to the direct toxicity of the active ingredient,the type of pesticide formulation and its specific composition can also affect the combined toxicity to environmental organisms.Toxicity assessment should also take into account the environmental behavior of pesticide formulations and systematically assess their actual environmental risks to ensure the objectivity of the evaluation.High-risk agents used in aquatic fields can be used to reduce their enrichment efficiency in gill tissues to achieve effective control of aquatic toxicity risk by using the selectivity of toxic potential differences caused by sedimentation behavior.