The Toxic Effects And Mechanism Of Pyrethroids On Different Life Stages Of Zebrafish

The toxicity of pesticides is not only depended on the physical and chemical properties,but also related to the biological species,life cycles and natural conditions.However,up to now,most of the aquatic toxicity assessments of pesticides had been based on biological single life stage,and no systematic or in-depth studies on the toxicity of biological multi stages.In this study,we selected tetramethrin?Tet?and fenpropathrin?Fen?as targeted compounds.Then we studied their toxicity and mechanism with zebrafish of three life stages?embryo,yolk-sac larvae and juvenile?.Enantioselective toxicity was further studied with pure enantiomers of Tet and Fen.Firstly,we selected enantiomeric pure Tet which was separated on selected chiral column by high performance liquid?HPLC?.Secondly,we studied their enantioselective in bioconcentration,development toxicity and thyroid interference effect of three life stages.The results are as follows:?1?Tet could be accumulated in zebrafish significantly,especially?-?-trans-Tet.The concentration of Tet in vivo ranged from 146.89 to 381.24 ng/g.There was no significant difference among the three life stages about biological enrichment factor?BCF?and it was concentration dependent.?2?The 96h-LC₅₀0 of Tet to zebrafish embryo and larvae was 0.57±0.66 and0.75±0.83 mg/L,respectively.But the 96h-LC₅₀0 of yolk-sac larvae was more than 1mg/L.The toxic order of three life stages to Tet was embryo>larvae>yolk-sac larvae.Moreover,a large suite of symptoms was induced in development of zebrafish after exposuring to Tet,including hatching inhibition,abnormal spontaneous movement,slow heart rate,growth regression and morphological deformities.The toxic order of the enantiomers was?+?-trans-Tet>?±?-trans-Tet>?-?-trans-Tet.?3?Tet could alter the expression of endocrine and congenital immune genes.?+?-trans-Tet up-regulated the transcription of Vtg genes in embryo and yolk-sac larvae.Cis-Tet up-regulated the transcription of immune genes in yolk-sac larvae and larvae.And?+?-trans-Tet showed stronger interferece effect than?-?-trans-Tet.Secondly,we selected enantiomeric pure Fen and studied their enantioselective toxicity in bioconcentration.The differences on developmental toxicity and thyroid-disrupting effects of three life stages were further studied.The results are as follows:?1?Fen could be accumulated in zebrafish and the bioaccumulation of them was concentration dependent,especially S-Fen.The concentration of Fen in vivo ranged from 0.8 to 99.35 ng/g.The order of BCF was larvae>yolk-sac>embryo.?2?The 96h-LC₅₀0 of Fen to zebrafish embryo and larvae and was 146.49±5.49,20.67±0.48 and 1.23±0.141mg/L,respectively.The toxic order of three life stages to Fen was larvae>yolk-sac larvae>embryo.Fen exposuring resulted in a series of malformation.Significant enantioselectivity was observed in the acute toxicity and development toxicity among the enantiomers of Fen.The toxic order of the enantiomers was S-Fen>cis-Fen>R-Fen.?3?Fen had a significant thyroid-disrupting effect on zebrafish.Compared with other life stages,Fen down-regulated the transcription of genes of TR?,Dio2,TG and NIS at larvae.Further analysis showed the mechanisms of Fen on three life stages were different.Fen disturbed the thyroid by alter the genes associated with dsyhormongenesis at embryo and yolk-sac larvae,but Fen alter thyroid metabolizing genes and thyroid transforming genes at larvae.And S-Fen showed stronger thyroid-disrupting effect than R-Fen.