Pesticide Inhalation Exposure, Air Concentration, and Droplet Size Spectra From Greenhouse Fogging

Abstract

ABSTRACT. Fogger application of pesticide in greenhouses canHand spraying with high-pressure, high-volume systems is the most common technique of pesticide application in greenhouse culture. However, fog or aerosol applications are feasible and often-used alternatives for enclosed structures. The motivations for fog application are the potential to increase spray deposition; improve pest control efficacy; and reduce application times, rates of active ingredients, and applicator exposure. A common fogging procedure in greenhouse operations is to apply the fog in late afternoon or early evening. This practice allows cultural workers to be absent from the greenhouse during and up to 12 to 16 h after application. Also, greenhouse vents may remain closed after application since nighttime temperatures are lower. Moreover, many applications are made by positioning the fogger within the greenhouse and allowing it to run unattended until the application is complete; the applicator can remain outside the structure during application. Anecdotally, fogging is often considered a hazardous application technique since the pesticide droplets are smaller and more concentrated than in conventional "wet" spraying techniques. Such reasoning may be valid; the potential inhalation hazard may exist. Practically, the potential hazard could be mitigated through establishment of appropriate re-entry intervals and use of respiratory protection with appropriate performance criteria for workers re-entering the structure. LITERATURE REVIEWA comprehensive study (Brouwer et al., 1992) reviewed previous work (e.g., Lindquist et al., 1987) concerning airborne concentration of pesticide following low-volume and fog application in greenhouses. Brouwer observed that the number and scope of previous studies were limited and a lack of information on greenhouse environmental conditions and droplet size spectra from application equipment made comparisons between studies invalid. Brouwer experimentally determined airborne pesticide concentrations up to 10 h post-application. Volatile insecticide (dichlorvos, v.p. = 1600 mPa) and nonvolatile fungicide (thiophanate-methyl, v.p. < 0.001 mPa) were applied using a mist (nonthermal) blower with a droplet size volume median diameter of 21 µm. The decrease in airborne concentration was described by a log-linear (i.e., an exponential decay) function. Concentration of the dichlorvos decreased by 90% during the first 3 h postapplication; the greenhouse was then vented and no further data recorded. Concentration of the thiophanate-methyl decreased by 99% in the 3-h post-application.Exploratory studies of airborne pesticide concentration in greenhouses have been conducted in California by the Worker Health and Safety Branch, California Department of Pesticide Regulation (formerly California Department of Food-and Agriculture), California Environmental Protection Agency. Rech and Edmiston (1988) monitored concentration of permethrin following thermal fog application of 0.24 kg a.i./ha. Air concentrations measured 1, ...

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