| As known,the chlorpyrifos and atrazine are widely used as the insecticide and herbicide in the production of agriculture,respectively.However,the chlorpyrifos and atrazine can enter water by several transition paths,such as the sedimentation,leaching,surface runoff,etc.,resulting in toxic effects on the tadpoles in frog class in a certain degree.The study on pesticide contamination is always the vital problem of the environmental toxicology.Therefore,in the present paper,Rana dybowskii and Rana amurensis were chosen to study the effects of the chlorpyrifos,atrazine and their combination on the acute toxicity of the two frogs.Based on the experiments on the acute toxicity,the effects of various concentrations of chlorpyrifos（0.43μg/L,4.3μg/L and 43μg/L for Rana dybowskii;0.364μg/L,3.64μg/L and 36.64μg/L for Rana amurensis）,atrazine（5.98μg/L,59.8μg/L,598μg/L for Rana dybowskii;7.499μg/L,74.99μg/L and 749.9μg/L for Rana amurensis）and their combination（0.532μg/L,5.32μg/L and 53.2μg/L for Rana dybowskii;0.432μg/L,4.32μg/L and 43.24μg/L for Rana amurensis）on the pathology of the organizational structure,growth and development,and anti-oxidation（CAT,GSH-Px,SOD and MDA）of both Rana dybowskii and Rana amurensis are studied in detail.The experimental results are listed as follows:1)Acute experimental results:in the water bath under heating at 1925 oC,the semi-lethal concentrations(LC50)of the Rana dybowskii tadpoles treated by the chlorpyrifos for 24 h,48 h,72 h and 96 h were 1.01 mg/L,0.90 mg/L,0.45 mg/L and0.21 mg/L,respectively（the safe concentration is 0.021 mg/L for the Rana dybowskii tadpoles）;the semi-lethal concentrations(LC50)of the Rana dybowskii tadpoles treated by the atrazine for 24 h,48 h,72 h and 96 h were 37.30 mg/L,18.05 mg/L,5.94 mg/L and 2.99 mg/L,respectively（the safe concentration is 0.299 mg/L for the Rana dybowskii tadpoles）;the semi-lethal concentrations(LC50)of the Rana dybowskii tadpoles treated by both the chlorpyrifos and atrazine for 24 h,48 h,72 h and 96 h were1.99 mg/L,0.81 mg/L,0.70 mg/L and 0.23 mg/L,respectively（the safe concentration is0.299 mg/L for the Rana dybowskii tadpoles）.The semi-lethal concentrations(LC50)of the Rana amurensis tadpoles treated by the chlorpyrifos for 24 h,48 h,72 h and 96 h were 2.09 mg/L,0.87 mg/L,0.39 mg/L and 0.18 mg/L,respectively（the safe concentration is 0.018 mg/L for the Rana amurensis tadpoles）;the semi-lethal concentrations(LC50)of the Rana amurensis tadpoles treated by the atrazine for 24 h,48 h,72 h and 96 h were 35.17 mg/L,13.38 mg/L,9.78 mg/L and 3.75 mg/L,respectively（the safe concentration is 0.375 mg/L for the Rana amurensis tadpoles）;the semi-lethal concentrations(LC50)of the Rana amurensis tadpoles treated by both the chlorpyrifos and atrazine for 24 h,48 h,72 h and 96 h were 2.50 mg/L,1.29 mg/L,0.48mg/L and 0.22 mg/L,respectively（the safe concentration is 0.022 mg/L for the Rana amurensis tadpoles）.The toxicity of Rana amurensis treated by the two pesticides was higher than that of Rana dybowskii treated by the two pesticides.2)Rana dybowskii and Rana amurensis were exposed in various concentrations of chlorpyrifos,atrazine and their combination mixed in 1:1 mass ratio for 7 d,14 d,21 d and 31 d for Rana dybowskii,and 7 d,14 d,21 d and 31 d for Rana amurensis,respectively.According to the observation based on the histopathology,the following conclusions were found:much strong toxic effects on both Rana dybowskii and Rana amurensis were produced under exposing in medium and high concentration of chlorpyrifos,atrazine and their combination solution,resulting in the changing of the morphological of the muscle tissue,which may be the mechanism producing the toxic effects of the chlorpyrifos and atrazine on both Rana dybowskii and Rana amurensis.Among them,the effects suffered of Rana amurensis were much more remarkable,which may be attributed to the slightly littler body type of Rana amurensis than that of Rana dybowskii.After the comparison experiments between the poisoning group and restoration group,it is found that the damages of the skin and muscle tissue of the restoration group were relieved and repaired largely,which behaved in evidence under the low concentration of pesticide.However,for the restoration group subjected to the joint effects of chlorpyrifos and atrazine,the symptom restored in a certain degree while the Pathological phenomena was still existed.3)According to the comparison between the effects of various concentrations（low-,medium-and high-concentration）of the chlorpyrifos,atrazine and their combination on Rana dybowskii and Rana amurensis,the following conclusions were found:the effects of the three various concentrations of pesticides on the body length of Rana（the poisoning group）weredifferent,whichdecreasedin theorder ofthe chlorpyrifos-atrazine mixture in 1:1 mass ratio,chlorpyrifos and atrazine.For the comparison between the poisoning group and restoration group after 31-day-treatment,the body lengths of the two Ranas subjected to medium-and high-concentration of chlorpyrifos and chlopyrifos-atrazine mixture in the restoration group were larger than those in the poisoning group and were similar with those in the control group.4)According to the comparison between the effects of various concentrations（low-,medium-and high-concentration）of the chlorpyrifos,atrazine and their combination on Rana dybowskii（for 7 days,14 days,21 days and 31 days,respectively）and Rana amurensis（for 7 days,14 days,21 days and 28 days,respectively）,the following conclusions were found:the oxidative stress mechanism of Rana dybowskii and Rana amurensis was activated by the treatment under various concentrations of pesticides for various days,resulting in the reductions of the enzyme activity of CAT,GSH and SOD and significant increase of the content of MDA.Furthermore,the free radicals and the antioxidant defense system of the organism were eliminated and destroyed,respectively,resulting in various organizations of Rana dybowskii and Rana amurensis suffered an oxidative damage and the normal physiological functions of the two Ranas were further influenced.This showed that the toxicity of the two pesticides was developed by destroying the antioxidant defense system.According to the comparison between the restoration group and poisoning group,it is found that the enzyme activity of CAT,GSH and SOD increased obviously and the content of MDA decreased,which showed that the anti-oxidation mechanism has been restored. |
