Faculty Bibliography

BACKGROUND: The present study was conducted among Chinese workers employed in glue- and shoe-making factories who had an average daily personal benzene exposure of 31+/-26 ppm (mean+/-SD). The metabolites monitored were S-phenylmercapturic acid (S-PMA), trans, trans-muconic acid (t,t-MA), hydroquinone (HQ), catechol (CAT), 1,2, 4-trihydroxybenzene (benzene triol, BT), and phenol. METHODS: S-PMA, t,t-MA, HQ, CAT, and BT were quantified by HPLC-tandem mass spectrometry. Phenol was measured by GC-MS. RESULTS: Levels of benzene metabolites (except BT) measured in urine samples collected from exposed workers at the end of workshift were significantly higher than those measured in unexposed subjects (P < 0.0001). The large increases in urinary metabolites from before to after work strongly correlated with benzene exposure. Concentrations of these metabolites in urine samples collected from exposed workers before work were also significantly higher than those from unexposed subjects. The half-lives of S-PMA, t,t-MA, HQ, CAT, and phenol were estimated from a time course study to be 12.8, 13.7, 12.7, 15.0, and 16.3 h, respectively. CONCLUSIONS: All metabolites, except BT, are good markers for benzene exposure at the observed levels; however, due to their high background, HQ, CAT, and phenol may not distinguish unexposed subjects from workers exposed to benzene at low ambient levels. S-PMA and t,t-MA are the most sensitive markers for low level benzene exposure.

Recent epidemiological evidence strongly suggests that ambient-particle-associated acidity is more closely correlated with total mortality and hospital admissions for respiratory disease than indices of total particulate mass. In addition, evidence is accumulating to support the hypothesis that the number of ultrafine (d < or = 200 nm) acid particles, rather than ambient mass, is an important determining factor affecting lung injury. Both outdoor and indoor air environments are dominated by nanometer-sized particles. However, no data are currently available on the size distribution or number concentration of acidic ambient ultrafine particles largely because there are no suitable methods for measuring these important quantities. We have developed a method to accomplish these measurements based on the use of iron nano-films for detection of acid droplets. Detectors were prepared by vapor deposition of iron onto 12-mm-diameter glass cover slips. The detectors develop reaction sites when exposed to H2SO4 or NH4HSO4 particles. Exposures to non-acidic particle (NaCl and [(NH4)]2SO4) result in no detectable surface deformations. The nano-films are examined with scanning probe microscopy (SPM) for the enumeration of reaction sites. Until recently, direct visualization of individual objects smaller than 200 nm has been possible only with electron microscopy. The advancement of SPM provides the opportunity to examine the detector surface features with high quality three dimensional imaging

Breathing zone samples are used to estimate worker exposure to airborne contaminants by collecting air from a vaguely defined zone surrounding the head. This zone is considered to have an airborne chemical concentration equivalent to the concentration breathed by the worker. It has been generally assumed that vapor is uniformly mixed in the breathing zone; therefore, samplers are placed on either lapel or on the chest of the worker. An extensive field investigation in a boat manufacturing plant was conducted where styrene air concentrations were measured by mounting four 3M one-stage diffusion samplers around the worker's breathing zone. Two job classes were studied: the spray gun operators and the rolling and tucking operators. Styrene air concentrations detected at the nose were significantly different than those concentrations detected at the other three locations and represented 90 percent, 84 percent, and 76 percent of the left lapel, right lapel, and chest samplers, respectively. This research revealed that the chest sampler provides a consistent relationship to the concentrations measured at the nose for a given job category. Additionally, this research identified the possible factors which could contribute to breathing zone concentration variations

The airborne particle and vapor phases of a volatile organic chemical (VOC) often coexist in the real workplace environment. Assessment of worker exposure to a VOC requires measuring not only the total airborne concentration but also the phase distribution because the deposition efficiency of the material in the respiratory tract will depend on the form in which it is inhaled. A prototype portable vapor/particle sampler (PVPS) has been designed for sampling and quantifying the phase distribution of volatile components in micrometer-sized airborne particles and coexisting gaseous phase based on differential inertia. The sampler was laboratory tested and validated. Tests included sampler performance assessment and comparison with current sampling methods for particles and organic vapors, i.e., glass fiber filter, charcoal sorbent tube, and diffusion monitors. The PVPS is a low-cost and lightweight device that can be driven by a single standard personal sampling pump. The mass quantities of materials collected by the sampler can be determined by standard analytical procedures. Combined with an appropriate size-selective inlet, the PVPS may be used as a personal inhalable or respirable volatile aerosol sampler for occupational VOC exposure assessment, especially in industrial, or household, spray work environments where the particle sizes are frequently large

The deposition of the unattached radon progeny in hollow cast models of the human tracheobronchial region was studied using iodine vapor. The experiments were conducted in a replicate cast whose inner surface was coated with NaOH impregnated charcoal powder. This coating can trap iodine molecules by converting iodine into iodide and iodate, so that the iodine gas molecules behave like particles and stick to the surface upon contact. The iodine vapor is selected as a surrogate of radon progeny because the effective diffusion coefficient of iodine vapor, 0.08 cm(2) s(-1), is close to the diffusivities of unattached radon progeny (0.03-0.07 cm(2) s(-1)). Deposition experiments have been conducted under constant and cyclic inspiratory Bow between 5 and 30 LPM. It was found that the deposition of iodine vapor under constant flow can be described by diffusion in laminar flow. The cyclic inspiratory flow pattern does not significantly change the total deposition in the tracheobronchial cast. This observation, combined with the enhanced particle deposition due to charge (Cohen ct al., 1996) suggest that particle charge plays an important role in the deposition of submicron particles in human airways. (C) 1998 American Association for Aerosol Research

The effect of a single electric charge on the efficiency with which ultrafine particles deposit in human airways has been investigated. When inhaled short-lived radon progeny are attached to electrically neutral particles their deposition efficiency is controlled by diffusion. But most ambient particles carry one, or a few, charges. We measured and compared the deposition (DE) of singly charged, charge-neutralized, and zero-charge 20-nm and 125-nm particles in hollow-cast models of human airways. These particle sizes were selected because they are about where modal peaks occur for the activity of the short-lived radon progeny in indoor air. For singly charged 20-nm particles deposition (+/- standard error) in the casts was 3.4 +/- 0.3 times that for charge neutralized aerosols and 5.3 +/- 0.3 times the amount deposited for zero-charged particles. Corresponding ratios for the 125-nm particles were 2.3 +/- 0.3 and 6.2 +/- 0.7. Since most ambient particles are charged this effect must be considered when models are used to predict dose from inhaled ultrafine particles