OCCUPATIONAL EXPOSURE TO 4,4'-BIPYRIDYL VAPOR AND AEROSOL DURING PARAQUAT MANUFACTURING

The mass concentrations of both vapor and aerosol phases of 4,4'-bipyr idyl were determined by a glass fiber filter and an XAD-2 tube in a pa raquat factory. The size distributions of 4,4'-bipyridyl aerosols and particles < 10 mu m were measured by a sis-stage cascade impactor: The mass concentrations of 4,4'-bipyridyl aerosols were in the range of 8 1.9 to 159.9 mg/m(3) with an average 4,4'-bipyridyl vapor mass concent ration of 3.1 mg/m(3) at the top of the open tank. On the average, the mass ratio of vapor phase to aerosol phase of 4,4'-bipyridyl was 0.02 5. Therefore, the aerosol phase is the major form of 4,4'-bipyridyl ex posure to the workers in this environment. Front the 4,4'-bipyridyl co ncentrations measured by the sampling systems of an XAD-2 tube alone a nd a filter followed by an XAD-2 tube, the 4,4'-bipyridyl aerosol coll ection efficiency of the XAD-2 tube was found to be approximately 50%. The average mass concentrations of less than 10 mu m aerosols and 4,4 '-bipyridyl aerosol in the occupational environment were 0.42 mg/m(3) and 1.26 mu g/m(3), respectively. The mass median aerodynamic diameter (geometric standard deviation) of particles < 10 mu m and 4,4'-bipyri dyl aerosol are 3.50 mu m (2.35) and 3.47 mu m (2.58), respectively. T he major mass fraction of 4,4'- bipyridyl aerosol occurred in the 3.3- 5.8 mu m size range. The enclosure efficiencies of a hood cover attach ed to a suction tube were found to be 88% and 82% for both aerosol and vapor phases of 4,4'-bipyridlyl, respectively. It is suggested that t he heterogeneous nucleation of 4,4'-bipyridyl and water vapor from the open tanks with subsequent coagulation is the major mechanism of aero sol formation. We conclude that both 4,4'-bipyridyl aerosol and vapor concentrations should be determined for the exposure assessment of the paraquat manufacturer in this workplace.