Airborne diazinon concentrations during and after outdoor spray application

Airborne concentrations of the organophosphate pesticide diazinon were assessed using personal sampling on an applicator and area sampling at several locations within ornamental plant beds sprayed with the chemical. As part of field work testing a prototype pesticide monitor, diazinon was applied to azalea bushes, from a backpack sprayer, on two separate occasions. Personal and area sampling was used to measure concentrations during the application and over multiple time scales after the initial sampling. The area measurements indicated that diazinon concentrations during and immediately after application were similar to the consensus occupational exposure limit (OEL) of 10 μg/m ³ for airborne diazinon. Concentrations measured from personal samples worn by the applicator were 57-82% of the occupational limit during the application period. Therefore, an applicator and anyone else near ornamental plants being sprayed with diazinon should use personal protective equipment, including appropriate respiratory protection. Concentrations declined substantially with time during the subsequent 24-hr period. In 2006, the U.S. Environmental Protection Agency (EPA) set the restricted-entry interval (REI) after diazinon is applied to ornamental plants to 2 days, assuming only dermal exposures are relevant after spraying. However, the results of this study suggest that the health risks posed by estimated potential doses caused by inhalation exposures after spraying are of the same order of magnitude as the risks posed by potential dermal doses using the risk assessment methodology employed by EPA. Thus, EPA should not dismiss inhalation exposures when developing REIs for diazinon in the future.