Acute Exposure Routes Of Pyraclostrobin In Zebrafish And Regulating Mechanism Of Reducing Toxicity By Microencapsulation

Strobilurin fungicides(Qo Is),serving as the first fungicide product type globally,were characterized by broad spectrum,high efficiency,low toxicity,safety,and unique mechanism of action and have effective bioactivity against diseases caused by species of deuteromycetes,oomycetes,ascomycetes,and basidiomycetes.However,they were highly toxic to aquatic organisms,which restricts their registration and application in paddy fields.It was studied that the toxicity of Qo I fungicides in aquatic organisms could be significantly reduced through constructing microencapsulated system.However,developing pesticide microcapsule(MC)delivery systems were focused on the prevention and control mechanism of MCs to target organisms,while the mechanisms of toxicity regulation in non-target organisms was rarely studied.Designing a targeted delivery and controlled release system based on the toxicological mechanism of pesticides in organisms can greatly improve the efficiency of developing effective and harmfulless product.In this study,pyraclostrobin,belonging to Qo I fungicides,was used as a model pesticide and zebrafish(Danio rerio)as a model organism.Identifying the exposure routes and target organs of pyraclostrobin in fish was the top priority to achieve those goals.According to toxic properties of pyraclostrobin in fish,the environmental behavior of pyraclostrobin-loaded MCs with different characteristic parameter such as release and settlement behavior in water,the relationship between accumulation of MCs in fish and their toxicity in the process of poisoning the fish was researched,thereby determining the targeting negative regulatory mechanisms of MC'formula and process parameters to their aquatic toxicity.The main results were as follows:1.The exposure routes and target organs of pyraclostrobin in zebrafishIn the study,we compared the effects of aquatic exposure,head immersion and trunk immersion on the toxicity and accumulation of pyraclostrobin in adult zebrafish.The results indicated there was almost no significant difference in the toxicity and accumulation level of pyraclostrobin in fish between aquatic exposure and head immersion,while trunk immersion resulted in a lower toxicity and accumulation level than other two exposure methods.The results suggested that pyraclostrobin accumulated in the fish body and then caused high toxicity in zebrafish mainly through the head rather than the trunk.Feeding poisonous feed test indicated that pyraclostrobin leaded to low toxicity in zebrafish via the alimentary canal.According to the results of the above four exposure routes,pyraclostrobin entered into fish mainly through the gill tissue of the head,thus causing high toxicity in fish.To determine the target organs of pyraclostrobin in zebrafish,we investigated the effects of pyraclostrobin on pathological damage and mitochondrial function of gill,heart and brain tissue in zebrafish via aquatic exposure and tail vein injection.The results showed that there was no significant difference in the toxicity level of pyraclostrobin in zebrafish between aquatic exposure and tail vein injection.After treated with two exposure methods,the obvious pathological damage was observed in the gills,including hyperplasia,curvature,adhesion,fusion,terminal enlargement,shrinkage,shortening,vacuolization,swelling of gill lamellae.However,there were no significant pathological changes in the heart or brain.In addition,damaged mitochondrial membrane potential occurred in the gill rather than heart or brain.The ATP content of three organs significantly decreased,and the complex III activity of the gill and heart tissue was significantly inhibited.The results suggested that although no obvious pathological and mitochondrial damage was observed in the heart and brain of zebrafish,the two organs suffered slight impact on energy supply.Considering the above results at the organic,cellular and biochemical levels,the most serious injury was seen in zebrafish gills,thus the gill was the predominant target organ of pyraclostrobin in adult zebrafish.2.The toxicity difference between Qo I and SDHI fungicides was positively correlated with the gill cytotoxicityThe 96 h-LC50 value of seven respiratory inhibitor fungicides to zebrafish was followed the rank order pyraclostrobin(0.048 mg/L)