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On the acute toxicity of fluoride to the larvae of Bufo gargarizans at different developmental stages

The purpose of this paper is to present our investigation results of the toxicity effects of fluoride ion(F-) on the larvae of Bufo gargarizans at different life stages,which will be useful to determine the sensitivity profile of species.For our research purpose,we have laid out our semi-static acute toxicity tests of F-to the larvae of B.gargarizans at different Gosner developmental stages(the stages of 23,26,30,36) to be conducted.The tadpoles at four Gosner developmental stages were arranged to be isolately exposed to F-with different concentrations,and the histological evaluations of liver from tadpoles exposed to 350 mg/L F-were detected.The results of our experiments show that the 96 h-LC50 of F-to the larvae of B.gargarizans at the Gosner developmental stages of 23,26,30,36 were equal to 689.11 mg/L,568.96 mg/L,495.42 mg/L,541.36 mg/L,with the safe mass concentrations being 6.89 mg/L,5.69 mg/L,4.95 mg/L,5.41 mg/L,respectively.At the same time,we have observed different sensitivities of larvae at different developmental stages to F-and found larvae at stage 30 more sensitive to fluoride than in other stages.However,Pearson correlation coefficients between safe concentration,the total length and body weight of larvae at different developmental stages were not significant(p0.05).On the other hand,the toxicity effects of fluoride were found to be influenced by the hardness of water used in the trial.As shown in the study,the 96 h-LC50 of larvae at stage 36 treated with distilled water and exposed to the tap water were found 492.32 mg/L and 541.36 mg/L,respectively.Moreover,exposed to the high concentration F-for the short periods,histological evaluations of liver reveals significant degeneration in structure and hepatocyte reduced significantly compared with the control.From the above results,it can be concluded that the larvae of B.gargarizans are sensitive to fluoride toxicity,hence more attention has to be paid to the toxic effects of fluoride in the water body to aquatic ecosystem.