Trace Metal Analysis of Atmospheric Aerosol Particle Size Fractions in Exhaled Human Breath Georges G. Desaedeleer and John W. Winchester Department of Oceanography, Florida State University, Tallahassee, Fla. 32306
The particle size distribution of lead, bromine, chlorine, and calcium in exhaled aerosols from a human subject breathing normally polluted air has been measured using proton-induced X-ray emission (PIXE) analysis. For all elements apparent respiratory disposition fractions decreased from both small and large particle sizes to a minimum near 0.5 pm aerodynamic equivalent diameter. A feasibility is demonstrated for direct determinations of trace element respiratory depositions in human subjects breathing aerosols a t ambient air concentrations.
Monitoring of air pollutants is generally carried out under the supposition that they are a hazard to human health, but measurements of the efficiency of uptake of air pollutants by the human respiratory tract are not extensive. This is especially true for uptake of trace metals carried by aerosol particles. From laboratory studies using monodisperse-generated aerosols of different sizes, it has been determined that smaller sizes are preferentially deposited deeper in the pulmonary region of the lung, whereas larger particles tend to be deposited along the respiratory tract (1-5). Theory predicts that larger particles are deposited by impaction and sedimentation from the moving air stream during breathing, with an efficiency which decreases with decreasing particle size, whereas the smallest particles are deposited during Brownian motion caused by molecular collisions while suspended in the air, with an efficiency which decreases with increasing particle size. A minimum in deposition efficiency is predicted for particles near 0.5-pm diameter, and laboratory findings are consistent with this prediction. Because of the expected strong dependence of respiratory deposition efficiency on particle size, some recent pollution aerosol research has been directed toward determining the distribution of toxic trace elements with particle size and relating these results with likely pollution source processes (6-8). Vapor condensation at high or ambient temperatures has been associated frequently with small particles whereas dispersion of dusts or liquids leads generally to larger particles. Because of the presumed public health importance of the size of particles on which an element is found (9, IO), as well as the total atmospheric concentration of the element ( I l ) , air quality standards may eventually be set in terms of particle size distribution of atmospheric concentration. Before this is done, however, it is desirable to make direct measurements of the efficiencies of uptake of trace elements by the human respiratory tract, testing human subjects breathing urban air containing pollution aerosols at ordinary concentrations. We report here a demonstrat,ion that it is feasible to make such a measurement, which hitherto has apparently not been reported in the literature.
Procedure An aerosol arrangement was designed around the requirements of high sensitivity proton-induced X-ray emission (PIXE) analysis (12-14) for trace elements from 16s to :ijBr by K X-ray detection and ssPb by L X-ray detection. In this method, a 4-MeV proton beam of 5-mm diameter
from a Van de Graaff accelerator is passed through an aerosol deposit on thin backing, and the shower of characteristic X rays is sorted using a Si(Li) detector and multichannel analyzer. The resulting spectrum is readily resolved into the elemental constituents, even for aerosols collected from only 100 liters of air. Our experiments in respiratory deposition of aerosols utilized two similar air sampling devices, one for sampling the ambient air directly and one into which the experimenter supplied all the air from his exhaled breath (Figure 1). Both devices were operated by a vacuum pump which drew air at constant rate by means of critical flow orifices. For the air-sampling devices we used cascade impactors of 5 and 6 stages, where each stage gave rise to a single small aerosol deposit suitable for PIXE analysis. Ambient and exhaled airs were each sampled by a pair of impactors operating at flow rates of 12 l./min and 1 l./min giving resolution down to a 0.5- and 0.25-wm diameter, respectively, on the impaction stages. The 50% cutoff diameters for unit density spherical particles on the stages plotted in Figures 2 and 3 are 4, 2, 1, 0.5, and 0.25 pm for stages 1-5 and filter stage 6 is for particles
