DDT (Dichlorodiphenyl-Trichloroacetic Acid)

Another environmental feature of DDT is its ubiquitous distribution in at least trace concentrations everywhere in the biosphere. This global contamination with DDT, and related chlorinated hydrocarbons such as PCBs, occurs because they enter into the atmospheric cycle and thereby become very widely distributed. This results from: (1) a slow evaporation of DDT from sprayed surfaces; (2) off-target drift of DDT when it is sprayed; and (3) entrainment by strong winds of DDT-contaminated dust into the atmosphere.

This ubiquitous contamination can be illustrated by the concentrations of DDT in animals in Antarctica, very far from places where it has been used. DDT concentrations of 5 ppm occur in fat of the southern polar skua, compared with less than 1 ppm in birds lower in the food web of the Southern Ocean such as the southern fulmar and species of penguin.

Much larger concentrations of DDT and other chlorinated hydrocarbons occur in predators living closer to places where the chemicals have been manufactured and used. The concentration of DDT in seals off the California coast was as much as 158 ppm in fat during the late 1960s. In the Baltic Sea of Europe residues in seals were up to 150 ppm, and off eastern Canada as much as 35 ppm occurred in seals and up to 520 ppm in porpoises.

Large residues of DDT also occur in predatory birds. Concentrations as high as 356 ppm (average of 12 ppm) occurred in bald eagles from the United States, up to 460 ppm in western grebes, and 131 ppm in herring gulls. White-tailed eagles in the Baltic Sea have had enormous residues—as much as 36,000 ppm of DDT and 17,000 ppm PCBs in fat, and eggs with up to 1,900 ppm DDT and 2,600 ppm PCBs.