Toxicity Of Pydiflumetofen To Three Aquatic Organisms And Its Risk Assessment For Aquatic Ecosystem

Pydiflumetofen is a new type of succinate dehydrogenase inhibitor（SDHI）fungicide,with broad-spectrum,high-efficiency fungicidal properties,which not only has a good effect on a variety of diseases of wheat,rape,peanut,tomato and other crops,but also has been reported to have excellent effects on rice blight and cachexia.As Pydiflumetofen is more and more widely used,its risk of entering the water environment is getting higher and higher,and it is very easy to cause potential risks to aquatic organisms.At present,most of the current studies on pydiflumetofen are focused on the activity against pathogenic bacteria and the efficacy against crop diseases,and there are fewer studies on the toxicity to aquatic organisms and the risks assessment of aquatic ecosystems.In this study,we used zebrafish、Daphnia magna and algaes as study object,explored the toxicity effects of pydiflumetofen on zebrafish adults,juveniles,embryos and on the early life stages of zebrafish,the growth inhibition toxicity of algaes,acute and reproductive toxicity to Daphnia magna,the toxicological data obtained in this study and the predicted environmental concentrations obtained from the TOP-RICE model were used to carry out a risk characterization analysis using the risk quotient method to comprehensively assess the risk of pydiflumetofen on aquatic ecosystem.（1）The acute toxicity test in zebrafish showed that pydiflumetofen was lethal to adults,juveniles and embryos,with 96 h-LC₅₀values of 0.584,0.314 and 0.642 mg a.i./L,showing that pydiflumetofen was highly toxic to all three stages of zebrafish,and the order of susceptibility to pydiflumetofen was juveniles>adults>embryos.Pydiflumetofen also caused abnormal development in zebrafish,affecting the 24 h voluntary movement of the embryo,reducing the number of heart beats,inhibiting the increase in body length,and causing malformations in the embryo,such as yolk sac edema and pericardial sac edema and so on.In zebrafish embryonic teratogenic effect 96 h-EC₅₀value 0.318 mg a.i./L.In zebrafish early life stage toxicity test pydiflumetofen had a 34 d-LC₅₀value of 0.184 mg a.i./L.In addition pydiflumetofen caused delayed hatching or failure of embryos,deformed juveniles and caused behavioral abnormalities,using the most sensitive indicator obtained The LOEC of pydiflumetofe on zebrafish early life stage（34 d）was 0.102 mg a.i./L and NOEC was 0.0819mg a.i./L.（2）Pydiflumetofen had growth inhibitory toxicity to all three plant algaes,which could slow down the growth of plant algaes,deform algal cells and cause yellowing of algal sap;its72h-E_rC₅₀values respectively were 7.35 mg a.i./L,10.8 mg a.i./L and 9.92 mg a.i./L to Pseudokirchneriella subcapitata,Scenedesmus obliquus and Chlorella vulgaris,which were all low in growth inhibition toxicity.（3）Pydiflumetofen was able to inhibit the activity inhibition of Daphnia magna,and the48h-EC₅₀value of Daphnia magna was 0.407 mg a.i./L,which was highly toxic in acute toxicity.In the 21d reproduction test,pydiflumetofen was able to affect the reproductive development indexes of Daphnia magna,which showed that the number of first and third Daphnia magna,the total number of Daphnia magna,the number of Daphnia magna fetuses,the number of molting times were reduced,the time of first and third Daphnia magna was prolonged,and the life span was shortened.Finally,the reproductive ability of Daphnia magna was evaluated by the reproduction of parental Daphnia magna,and the LOEC of Daphnia magna on 21 d reproduction was 0.0412 mg a.i./L and NOEC was 0.0217 mg a.i./L.（4）The results of the risk assessment of pydiflumetofen on aquatic ecosystems showed that when the application method is seed treatment（20 g a.i./100 kg rice seed）pydiflumetofen has an acceptable risk of toxicity to vertebrates,invertebrates,and primary producers.When applied at a rate of 160 g a.i./hm²with one application and stem and leaf spray,the toxicity risk for primary producers was acceptable for pydiflumetofen;for vertebrates and invertebrates the toxicity risk is unacceptable for the early-leaf growth,early-tillering,early-elevation,late leaf growth and late tillering scenarios,except for the late rice-pulling application where the toxicity risk is acceptable.The toxicity risk of pydiflumetofen to primary producers was acceptable when applied at 200 g a.i./hm²,two applications,7 days apart,and stem and leaf spray;the toxicity risk was unacceptable for both vertebrates and invertebrates.In summary,pydiflumetofen showed high toxicity to all stages of zebrafish and Daphnia magna,but low toxicity to algaes;the risk assessment results showed that pydiflumetofen had a high risk to vertebrates and invertebrates when used as a stem and leaf spray to control rice diseases,while the toxicity risk to both vertebrates and invertebrates was acceptable when used as a seed treatment.This study provides a scientific reference for the rational application and efficient management of pydiflumetofen.