| Recent years,chlorpyrifos and atrazine are widely noticed because of their large amount of use,long residual period,high detection rate of water environment and some toxicity effects on animals.At the same time,the widespread use of the two pesticides is also an important factor causing water and soil pollution.To enrich the toxicological data of the two pesticides on aquatic vertebrates,this paper studied the acute toxicity of single and combined exposure on Oryzias latipes.In addition,this study also investigated effects of sub-chronic exposure of atrazine and chlorpyrifos,atrazine(12.04 ?g/L,120.40 ?g/L and 1204.00 ?g/L),chlorpyrifos(1.06 ?g/L,10.60 ?g/L and106.00 ?g/L)and the combined exposure(1.01 ?g/L,10.10 ?g/L and 101.00 ?g/L)on growth(length,weight),on antioxidant(SOD,GSH-PX,CAT,MDA),and gene expression(bcl6b).The results showed that:1.The study of acute toxicity of atrazine and chlorpyrifos on Oryzias latipes demonstrated that LC50 of atrazine tested in different time points were 25.305 mg/L(24h),16.023 mg/L(48 h),10.444 mg/L(72 h),6.109 mg/L(96 h),while LC50 of chlorpyrifos were 1.488 mg/L(24 h),1.117 mg/L(48 h),0.773 mg/L(72 h),0.530 mg/L(96 h),and LC50 of the two combined exposure,concentration ratio of 1:1,were 1.096mg/L(24 h),0.868 mg/L(48 h),0.674 mg/L(72 h),0.506 mg/L(96 h),respectively.Safe concentrations were 0.602,0.053 and 0.051 mg/L,respectively.Toxicity level followed moderate toxicity,high toxicity and high toxicity according to pesticide toxicity grading criteria.2.Single and combined exposure of atrazine and chlorpyrifos,The length and weight of Oryzias latipes in the treatment group were significantly lower than those in the control group(P < 0.05),and with the concentration of the pesticide increased and the time of exposure increased,the length and weight of the Oryzias latipes significantly inhibited(P < 0.05).The length and weight of Oryzias latipes inhibition rates of the high concentration groups at the end of the exposure period were: atrazine15.9% and 26.9%,chlorpyrifos 17.1% and 27.8%,the mixture of them 17.3% and31.0%.3.Single and combined exposure of atrazine and chlorpyrifos could damage oxidative stress of Oryzias latipes,decreased the activities of SOD,GSH-PX,CAT,and increased MDA content(P < 0.05),there by destroyed antioxidant defense system,resulted in oxidative damage of Oryzias latipes tissues and affected their normal physiological function.The activities of SOD,GSH-PX and CAT of Oryzias latipes were significantly increased(P < 0.05),while the MDA content was significantly decreased(P < 0.05),as compared to their counterparts at the end of recovery.4.Single and combined exposure of atrazine and chlorpyrifos could affect the expression of bcl6b mRNA in muscle and digestive tract tissue of Oryzias latipes.With the extension of the exposure time and the increase of the concentration,bcl6b mRNA expression was significantly increased in the muscle and digestive tract tissue(P < 0.05).At the end of recovery,bcl6b mRNA expression was significantly down-regulated in the muscle and digestive tract tissue of Oryzias latipes(P < 0.05).In conclusion,atrazine and chlorpyrifos were highly toxic and toxic pesticides to Oryzias latipes.Single and combined exposure of atrazine and chlorpyrifos will produce toxic effect,inhibit the growth,and inhibit the activities of antioxidant enzymes(SOD,GSH-PX and CAT)in tissues,promote the increase of MDA content,causing oxidative damage on Oryzias latipes,destroying antioxidant defense system.At the same time,the expression of bcl6b mRNA was significantly up-regulated,indicating that there is an internal relationship between bcl6b mRNA expression and the activities of antioxidant enzymes.After the environmental conditions are improved,the growth,the activities of antioxidant enzymes(SOD,GSH-PX and CAT)and the expression of bcl6b mRNA will be effectively restored. |
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