The Trend of DDT and Parathion Residues on Apples Grown in Central Washington1

A study was carried out in 1958 to determine the average amounts of DDT and parathion residue on apples in central Washington and to compare these residues with those found in past years when fewer and earlier sprays and lower dosages were used. The DDT residue levels ranged from 0.8 to 12.4 p.p.m. with a mean of 8.0 p.p.m. for all samples, both washed and unwashed. For each variety and for all samples considered together, the unwashed apples had a higher DDT residue than the washed samples. Only nine of the unwashed samples (15.2%) and 1 washed sample (1.6%) had residues above the 7 p.p.m. tolerance level. Parathion residue ranged from 0.01 to 0.32 p.p.m. with a mean of 0.10 p.p.m. The residue values for both DDT and parathion reported here are somewhat higher than those reported for earlier years by various workers. With an increase in number of cover sprays applied, a corresponding increase in DDT residue was observed. Washing was found to lower the DDT residue level, but little difference between washing with and without brushes was apparent.