Abstract
The mass concentrations of both vapor and aerosol phases of 4,4′ -bipyridyl were determined by a glass fiber filter and an XAD-2 tube in a paraquat factory. The size distributions of 4,4′ -bipyridyl aerosols and particles <10 µm were measured by a six-stage cascade impactor. The mass concentrations of 4,4′ -bipyridyl aerosols were in the range of 81.9 to 159.9 mg/m3 with an average 4,4′ -bipyridyl vapor mass concentration of 3.1 mg/m3 at the top of the open tank. On the average, the mass ratio of vapor phase to aerosol phase of 4,4′ -bipyridyl was 0.025. Therefore, the aerosol phase is the major form of 4,4′ -bipyridyl exposure to the workers in this environment. From the 4,4′ -bipyridyl concentrations measured by the sampling systems of an XAD-2 tube alone and a filter followed by an XAD-2 tube, the 4,4′ -bipyridyl aerosol collection efficiency of the XAD-2 tube was found to be approximately 50%. The average mass concentrations of less than 10 µm aerosols and 4,4′ -bipyridyl aerosol in the occupational environment were 0.42 mg/m3 and 1.26 µg/m3, respectively. The mass median aerodynamic diameter (geometric standard deviation) of particles <10 µm and 4,4′ -bipyridyl aerosol are 3.50 µm (2.35) and 3.47 µm (2.58), respectively. The major mass fraction of 4,4′ -bipyridyl aerosol occurred in the 3.3–5.8 µm she range. The enclosure efficiencies of a hood cover attached to a suction tube were found to be 88% and 82% for both aerosol and vapor phases of 4,4′ -bipyridyl, respectively. It is suggested that the heterogeneous nucleation of 4,4′ -bipyridyl and water vapor from the open tanks with subsequent coagulation is the major mechanism of aerosol formation. We conclude that both 4,4′ -bipyridyl aerosol and vapor concentration should be determined for the exposure assessment of the paraquat manufacturer in this workplace.