The Ld50 Median Lethal Dose And Lc50 Median Lethal Concentration Toxicity Tests PDF Download

The U.S. Environmental Protection Agency (EPA) requires that the results of certain toxicity tests on wildlife and aquatic organisms be submitted to the agency for evaluation before a new pesticide can be federally registered. The results of these toxicity tests are used to address the potential acute hazards of a pesticide's use to wildlife and aquatic organisms. At the present time an acceptable short-term feeding method for small mammals is not available. The EPA has been using the results of data submitted to support human safety requirements [primarily the rat single-dose oral median lethal dosage (LD50) data] to assess the hazards of pesticide residues in and on food to mammalian wildlife. We believe that these data may not properly represent the toxicity of a pesticide residue to mammalian wildlife. The objectives of the present study were three-fold: (1) to develop an acceptable short-term dietary LC50 test for small mammals, (2) to evaluate the test method by testing a number of chemical pesticides, and (3) to determine the relationship between the rat LD50 and median lethal concentration (LC50) values. The proposed 5-day LC50 test uses laboratory rats (Wistar strain) and is similar to a published avian dietary LC50 study. It consists of a 5-day acclimation period, a 5-day exposure to treated food, and a posttreatment observation period lasting for at least 9 days. The initial studies involved the exposure of five male and five female rat groups to each of five concentrations of treated food and one untreated group for control. The mortality, body weights, and food consumption were recorded. The mortality data were used to calculate LC50 values, which are presented for 17 pesticides. The experimentally determined LC50 values for rats were compared with derived ones calculated from published rat LD50 values. The derived values were not toxicologically equivalent to the LC50 values determined from our tests. Data are presented that indicate to us that rat LC50 values are a better measure of the toxicity of pesticide residues to mammalian wildlife than are rat LD50 values. Incorrect decisions on acute hazards of pesticide residues can result from the use of rat LC50 values calculated from rat LD50 values.