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SOURCE ASSESSMENT: DEFOLIATION OF COTTON, STATE-OF-THE ART
Citation:
Peters, J. AND T. Blackwood. SOURCE ASSESSMENT: DEFOLIATION OF COTTON, STATE-OF-THE ART. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/2-77/107g.
Description:
The report describes a study of air pollutants emitted during the defoliation or desiccation of cotton prior to harvest. (Defoliation is the process by which leaves are abscissed from the plant by the action of topically applied chemical agents. Desiccation by chemicals is the drying or rapid killing of the leaf blades and petioles with the leaves remaining in a withered state on the plant.) Emissions of defoliants were DEF, Folex, and sodium chlorate. Emissions of desiccants were arsenic acid and paraquat. Source severity for emissions from a representative source were 0.69 + or -0.32 for arsenic acid, 0.30 for paraquat, 0.44 for sodium chlorate, and 0.67 for DEF. (Source severity is a measure of the hazard potential of a representative emission source; for this source type, it was defined as the ratio of the time-averaged ground level concentration of the species emitted at the downwind perimeter of a representative field undergoing spraying for defoliation or desiccation, to a time-adjusted exposure factor related to TLV.) Existing control technology for aerial application of pesticides includes the use of fluid additives and nozzle design/orientation to reduce chemical drift. Future control technology considerations include the use of foam spray systems, multiple needle nozzle systems, and the replacement of chemical defoliation with thermal defoliation.