Ecotoxicological Effects Of Sulfoxaflor In Soil

Neonicotinoids are considered as one of the most important insecticides in China and worldwide.However,the wide application of neonicotinoids has a negative impact on soil and some non-target organisms,and poses a threat to the ecological environment,especially the farmland ecosystem.As the fourth generation of neonicotinoids,sulfoxaflor is of great application value due to its good insecticidal effect and low cross resistance.It has been registered and approved in more than 40 countries around the world since 2010.After the application in the field,only a small amount of sulfoxaflor acts on the target;and most enters soil,which becomes the most important destination of sulfoxaflor in the environment.At present,the related research mainly focuses on the biological characteristics,mechanism of action,metabolism,and residue determination of sulfoxaflor.Few reports can be found on its environmental safety risk.While soil is the most important medium for the degradation and transformation of sulfoxaflor,it is still unclear whether sulfoxaflor has adverse effects on soil.Therefore,the current work mainly studies:(1)The analytical method for the determination of sulfoxaflor in different samples;(2)Degradation rules of sulfoxaflor in different soil types;(3)Lethal toxicity and sublethal metabolic interference effect of sulfoxaflor on earthworm;(4)Effects of sulfoxaflor on greenhouse gas(N₂O)emissions from vegetable soil and its microbial driving mechanism.The main results are as follows:(1)A method for the determination of sulfoxaflor in different samples was established.The average recoveries of sulfoxaflor in soil,earthworm and tobacco are 87.87?101.67%with RSD of 2.34?8.94%.The limits of detection(LOD)and quantification(LOQ)are 0.003mg/kg and 0.01 mg/kg,respectively.The method meets the requirements of pesticide residue detection in terms of accuracy,precision,reproducibility,and other parameters,and can be used for the determination of sulfoxaflor in soils,non-target animal(earthworm)and tobacco samples.(2)The degradation dynamics of sulfoxaflor in soils and tobacco leaves were revealed.Sulfoxaflor was rapidly digested in soils and tobacco,in contrast to no significant change in the control(solvents).The degradation curve,plotted by residual concentrations and time,is in accordance with the first-order kinetic equation with the values of R²being greater than0.90.The degradation half-life(T_1/2)of sulfoxaflor in soils and tobacco leaves ranges from2.97 to 6.48 days,and the degradation rate is greater than 90%after 21 days of application.(3)The acute toxicity of sulfoxaflor to earthworm was evaluated,as well as the sublethal metabolic interference effect.Sulfoxaflor is highly toxic to earthworms and is easily bioaccumulated in earthworms.Sublethal doses of sulfoxaflor cause server oxidative damage to earthworms,as indicated by that the activities of SOD,CAT,and GST decrease significantly and the content of MDA increases.Metabolites and metabolic pathway analysis show that sulfoxaflor significantly affects the contents of 26 metabolites in earthworms and activates energy metabolism and urea cycle pathways,inhibiting nucleotide metabolism and possibly leading to further DNA damage.The results show that earthworm might be a new entry point for sulfoxaflor to enter the food chain of wild animals.Considering that earthworms have a great effect on soil functions and the ecosystem,the high safety risk of sulfoxaflor may extend from earthworm to the environment.(4)The effects of sulfoxaflor on N₂O emissions from greenhouse vegetable soils and its microbial driving mechanism were studied.Microbial degradation is the main driving factor for the degradation of sulfoxaflor in soil.The recommended dosage of sulfoxaflor could lead to the consumption of NO₃^--N,the accumulation of NH₄⁺-N,and a significant the increase of N₂O emission rate.Meanwhile,sulfoxaflor significantly increases the abundance of soil denitrifying microorganisms with nir K,nir S and nos Z genes and changes the community structure of denitrifying bacteria,but shows no significant effect on nitrifying bacteria,i.e.AOA-amo A and AOB-amo A.N₂O emission rate is correlated with gene abundance of denitrifying microorganisms.Sulfoxaflor may affect the dynamic balance of the production and consumption of N₂O in the process of soil microbial denitrification,resulting in a significant increase in N₂O emissions.In conclusion,sulfoxaflor is an easily degradable pesticide and quickly digested in soil.However,sulfoxaflor has high toxicity to non-target earthworms in soil and is prone to be bioaccumulated in earthworms.At the same time,sulfoxaflor can significantly affect the denitrifying microbial community structure in soil and promote the emission of greenhouse gas N₂O.In view of these results,sulfoxaflor demonstrates some negative ecotoxicological effects on soil.Therefore,more attention should be paid to the safety risk of sulfoxaflor on soil.This study elucidated the ecotoxicological effects of sulfoxaflor on soil in terms of the degradation law and the effects on soil animal(earthworms)and soil microorganisms.It provides preliminary data for comprehensive assessment of ecological risk assessment of sulfoxaflor contaminated soil and the theoretical basis for the safety of sulfoxaflor application and soil pollution control.