Distribution and Settling Rate of CO2-Propelled Micronized Insecticidal Dusts in Aircraft2

Abstract

Distribution and rate of settling of a micronized dust (42.5% DDT, 42.5% carbaryl, 15% silica) applied at rates of 1 or 2 g/1000 ft3 in the cargo compartments of aircraft to kill agricultural insects were studied. Samples of air taken at 15-, 30-, 60-, and 120-minute intervals after treatment were analyzed for both insecticides. At 30 and 60 min posttreatment, the levels of dust in the air did not differ significantly for either the 1- or the 2-g treatment rate (3.31 and 0.0 μ per liter, respectively, vs. 2.96 and 0.30 μg per liter, respectively). Circulation of air did not affect the rate of settling. Petri dishes spaced at 10-foot intervals the length of the compartment were analyzed to determine the pattern of distribution. Dust settled rapidly without air circulation, and the technique gave highly effective coverage (dust traveled at least 90 ft from the expulsion apparatus). Later tests in which air samples were collected from aircraft which had received 8–10 treatments over a 2-month interval indicated no resuspension or accumulation of dust after repeated treatment.