Residue analysis of forest soils sprayed once at 1 lb/acre showed little breakdown of DDT through 9 years after application. In the absence of appreciable downward trend, residue persistence could not be estimated beyond stating that it appears to persist much longer than the 10 years suggested by others. Persistent residues are largely restricted to the upper soil litter. Residues pass from soils to earthworms to robins throughout the 9-year period studied. It is suggested that this relationship may persist for as long as 30 years after a single application to the forest. Biological magnification of residues in robins is demonstrated. Significance of these residue levels is discussed.

DDT residues were measured by gas chromatography in crayfish collected in streams sprayed a single time but in various past years, in streams sprayed two and three times, and in streams never sprayed. Residues in the year of treatment ranged from 0.5 to 2.5 ppm. By 2 yr after treatment, residues had declined to about 0.1 ppm but remained near this level through 9 yr after treatment. Grayfish in unsprayed streams carries uniformly low residues, 0.009—0.014 ppm. Prolonged contamination in crayfish in sprayed watersheds apparently derives from highly persistent soil residues. Ecological significance of these residue levels is discussed.

No abstract

DDT (dichloro‐dipenyl‐trichloroethene) was used between 1954 and 1967 for the control of spruce budworm (Choristoneura fumiferana) in northern Maine. Soils originally tested in 1967 were resampled in 1973 and 1976 to help clarify the degree of persistence of DDT in northern spodosols. Soils from areas sprayed three times at 1.12 kg/ha continue to contain up to 4.5 ppm DDT residues 12 years after application. Pesticide levels in the soils sampled in 1973 and 1976 were not significantly different from levels measured in 1967. Also, analyses of soil profile samples through the A and B horizons indicated that >96% of the residues were still located in the O1 and O2 horizons.