Tissue residues of dieldrin in relation to mortality in birds and mammals
An experiment was performed with Coturnix to learn what residue levels were indicative of death from dieldrin poisoning. Birds were fed diets containing 250, 50, 10, and 2 ppm dieldrin for periods up to 158 days. The dieldrin was 95% pure HEOD, which is 1,2,3,4,10,10-hexachloro-6, 7.epoxy. l,4,4a,5,6,7,8,8a-octahydro-l,4-endo,exo-5,8- dimethanonaphthalene. When half of a group was dead, the other half was sacrificed for comparison of residues in dead and survivors. Dosage levels controlled time to death, but did not control residue levels in the dead. Residues in liver and carcass proved to be misleading and complicated by changes in lipid content. Brain residues correlated well with death although residues in dead and survivors overlapped. Brain residues of animals killed by dieldrin in the field and in other experiments are listed. Data agree in general for several species of birds and mammals. There is evidence, however, for species differences in average lethal brain residues. It is concluded that brain residues of 4 or 5 ppm (wet weight) or higher indicate that the animal was in the known danger zone and may have died from dieldrin. Brain residues averaged lower in wild than in experimental animals. Possible explanations include species differences, more stress and exertion in the wild, and overrepresentation in the field series of individuals that will die with low but lethal brain residues. The latter is supported by the fact that the first Coturnix to die in each sex and treatment group had the lowest brain residue of its group. Birds receiving 2 ppm dieldrin, and some receiving 10 ppm, were able to maintain low brain residues throughout the experiment. However, birds of the 10 ppm group could withstand little stress and mobilization of toxicant, for a few micrograms in the brain were lethal and bodies contained hundreds or thousands of micrograms.