| Sulfoxaflor(SFX)is a promising neonicotinoid due to its insecticidal efficacy and low cross-resistance and will metabolize more toxic compounds in the environment than it does.Daphnia magna is a model organism with a transparent body and a sensitive response to toxicity,and is widely distributed worldwide.In this paper we investigate the toxicity of SFX and its main metabolites X11719474(X474)and X11519540(X540)to Daphnia magna,including acute toxicity,growth and reproduction,swimming behavior,oxidative stress and a transcriptomic analysis of their molecular mechanisms of action on Daphnia magna.This study provides a scientific basis and theoretical rationale for the toxicological safety evaluation of SFX in aquatic animals.The main study contents and conclusions are as follows:1.The results of the acute toxicity test showed that the LC50 values of SFX and its metabolites X540 and X474 on Daphnia magna at 48 h were 17.26,7.03 and 0.61 mg/L,respectively.According to the pesticide toxicity classification criteria,it can be seen that SFX is a low toxicity pesticide for Daphnia magna,while its metabolites X540 and X474 are toxic toxicity and high toxicity,respectively.Meanwhile,we also studied the combined effect of their binary ternary mixture on Daphnia magna and found that it basically showed a synergistic effect.Based on the results of the acute toxicity experiments,two experimental concentrations(1/100 LC50 and 1/10 LC50)were set to investigate the effects of SFX and its metabolites X540 and X474 on the growth inhibition of Daphnia magna.21 d exposure time ended with significant inhibition of body length,reproduction and firstborn birth time at low and high concentrations compared to the control group.2.The effects of SFX and its metabolites X540 and X474 on the swimming behavior of Daphnia magna were investigated.Compared with the control group,SFX and X540 basically showed activating effects,except for X474 which had inhibiting effects on the swimming speed and distance of Daphnia magna.In addition,the effects of SFX and its metabolites X540 and X474 on the antioxidant enzymes(SOD,CAT),AchE enzyme activity and MDA content of Daphnia magna were investigated.Compared with the control group,the antioxidant enzymes of SFX and X540 and X474 showed an induced activation effect on Daphnia magna,while the MDA content varied depending on the drug treatment.This indicates that SFX and its metabolites X540 and X474 can cause some degree of damage to Daphnia magna.3.SFX and its metabolites X540 and X474 had an effect on gene expression after 48 h exposure to Daphnia magna,in particular,the greatest difference in a number of down-and up-regulated genes was detected between the SFX treatment and the control,amounting to a total of 613 genes.The smallest significant number of regulated genes was found between the X474 treatment and the control,with 46 and 200 significantly up-and down-regulated genes,respectively.In addition,by KEGG enrichment analysis we found that SFX,X540 and X474 affected the progestinmediated oocyte maturation pathway and that X474 affected this pathway to the greatest extent of the three compounds,thus inferring that D.magna treated with X474 had lower reproductive capacity than those treated with the other two compounds.This suggests that SFX and its metabolites have a disruptive effect on Daphnia magna reproduction. |
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