DDT residues in air in the Mississippi delta, 1975.

In a previous publication the authors reported on 88 percent decrease in sigma DDT (DDT plus metabolities) in air between 1972 and 1974 in the Mississippi Delta. This period was the first two years after the use of DDT was banned in the United States. The present report shows an additional 36 percent decrease in sigma DDT levels in air between 1974 and 1975. Thus in the past three years sigma DDT in air has decreased by 92 percent, a much more rapid decrease than had been expected.