DDE and DDD residues correlated with mortality of experimental birds

Nearly everywhere in nature are found DDE and DDD, which are metabolites of DDT, and they often become concentrated through food chains. DDD is also a commercial insecticide. large amounts of both are frequently found in birds, but the significance of these amounts has puzzled many owrkers. Studies at Clear Lake, California^1 gave some data on DDD danger levels, but less is known of DDE, the member of the DDT group that is most frequent and most abundant in nature. Although DDE is toxic, relatively alrge residues are found in apparently healthy animals. As one step in untanglig the problem, it seemed important to determine the residue levels that indicate danger to life. earlier work with DDR and dieldrin has shown the value of this approach.^{2-5, 1 2}