Evaluation of Acute Toxicity of Lead Acetate, Mercury Chloride, and Their Effects on Fasting Blood Glucose Level in the Common African Toad (Bufo regularis)

Abstract

: Mercury and lead are heavy metals found in the environment which affect metabolic activity. However, few studies have investigated the acute toxicity tests for mercury chloride and lead acetate in amphibians. The present study evaluated acute toxicity values of lead acetate, mercury chloride and their effects on fasting blood glucose levels in the common African toad Bufo regularis. The acute toxicity test was performed using static renewal bioassays. A total of 90 adult toads of either sex was used for the study. The experiment was divided into two phases. Phase 1 study consisted of 50 toads divided into 10 groups of 5 toads per group. Animals in groups 1-5 were exposed to water (0mg/L), 4mg/L, 8mg/L, 16mg/L and 32mg/L of lead acetate solutions respectively while animals in groups 6-10 were exposed to water (0mg/L), 10mg/L, 20mg/L, 35mg/L, 50mg/L of mercury chloride solutions respectively for 96 hours. Mortality was recorded after 96h and LD50 values were calculated. The second phase of the experiment had 40 toads divided into eight groups of five animals each. Animals in groups 1-4 were exposed to sub lethal concentrations of mercury chloride 0mg/L, 1mg/L, 2mg/L, 3mg/L and 4mg/L while groups 5-8 animals were exposed to sub lethal concentrations of lead acetate 0mg/L, 1mg/L, 2mg/L, 3mg/L, and 4mg/L respectively for 7 days. The blood glucose level was measured one week after exposure using the modified glucose oxidase method. The results of the study showed the 96h LD50 values for mercury chloride was 43mg/L and 15.03mg/L for lead acetate in the common African toad. Acute exposure to low dose mercury chloride and lead acetate solutions caused a significant increase in fasting glucose levels of the toads compared with the controls. In conclusion, the study showed the 96h LD50 values for lead acetate was 15.03mg/L and 43mg/L for mercury chloride in the common African toad. This study also, demonstrated that acute exposure to low dose lead acetate and mercury chloride solutions caused harmful effects and increased fasting glucose levels in the common African toad. Therefore, it is suggested that exposure to lead acetate and mercury chloride be avoided.