Urinary excretion of unmetabolized acetone as an indicator of occupational exposure to acetone.

Acetone concentrations in urine samples from 28 workers exposed to acetone in a fiber-reinforced plastics factory were determined by directly injecting urine supernate into a gaschromatograph with FID detectors. Acetone concentrations in the urine from ten nonexposed subjects were also determined. The 8-h time-weighted exposure intensity of individual workers was monitored by means of diffusive sampling. Acetone concentration in urine and acetone concentration in the breathing zone showed a linear correlation to each other. The study results indicate that the correlation coefficient is high enough to enable use of the urinary level of acetone as an indicator of occupational exposure to acetone.

A real-time method to evaluate the nasal deposition and clearance of acetone in the human volunteer.

Nasal dosimetry models have become increasingly quantitative as insights into tissue deposition/clearance and computational fluid dynamics have become available. Validation of these models requires sufficient experimental data. However, investigations into respiratory deposition, particularly in human volunteers, have been historically limited due to methodological limitations. To overcome this, a method for evaluating the nasal wash-in, wash-out phenomena of a highly water-soluble compound in human volunteers was developed and characterized. This methodology was assessed using controlled human inhalation exposures to uniformly labeled [(13)C]acetone at approximately 1 ppm concentration for 30 min under different breathing maneuvers (inhale nose/exhale nose; inhale nose/exhale mouth; inhale mouth/exhale nose). A small-diameter air-sampling probe inserted in the nasopharyngeal cavity of the volunteer was connected directly to an ion-trap mass spectrometer capable of sampling every 0.8 s. A second ion-trap mass spectrometer simultaneously sampled from the volunteer's exhaled breath stream via a breath-inlet device interface. Together, the two mass spectrometers provided real-time appraisal of the [(13)C]acetone concentrations in the nasopharyngeal region and in the exhaled breath stream before, during, and after the different breathing maneuvers. The breathing cycle (depth and frequency) and heart rate were concurrently monitored throughout the exposure using a heart-rate monitor and a human plethysmograph to differentiate inhalation and exhalation. Graphical overlay of the plethysmography results with the mass spectrometer measurements show clear quantifiable differences in [(13)C]acetone levels at the nasal probe as a function of breathing maneuvers. Breath-by-breath analyses of [(13)C]acetone concentrations indicate that between 40 and 75% of the compound is absorbed upon inhalation and nearly all of that absorbed is released back into the breath stream during exhalation.

Clearance concepts applied to the metabolism of inhaled vapors in tissues lining the nasal cavity.

Some inhaled vapors are metabolized by tissues in the nasal cavity or carried away in nasal venous blood after diffusing from the lumen through the nasal epithelial tissues. These processes remove chemical from the airstream. Clearance (volume/time) is the volumetric airflow from which chemical would have to be completely removed to account for the net loss. We present here a steady-state analysis of a series of physiologically based clearance-extraction (PBCE) models for nasal clearance of inhaled vapors, consisting of one, two, three, or four subcompartments. A two-compartment model is the simplest representation of tissues in the nasal cavity, with an air and a tissue compartment. The three-compartment model had air, mucus, and tissue phases. The four-compartment model included both epithelial and submucosal tissues in addition to the air and mucus compartments. For the two-, three-, and four-compartment models, the airstream clearance (Cl(sys)) equation has a common form. Cl(sys) = Cl(tot)H(m:a)PA(gas)Q divided by Cl(tot)H(m:a)(Q + PA(gas)) + PA(gas)Q. In this equation, Cl(tot) is the total tissue clearance, PA(gas) is the gas-phase diffusional clearance, Q is the airflow, and H(muc:a) is the mucus air partition coefficient. Cl(tot) varies in complexity for the different models since it encompasses tissue diffusion, tissue clearance due to metabolism, and blood flow. A physiologically based clearance-extraction (PBCE) model for the whole nose with three nasal tissue regions, each containing a four-compartment tissue stack, was used to simulate nasal uptake of three vapors-acetone, methyl methacrylate (MMA), and vinyl acetate (VA)-to show the dependence of clearance on different parameters for specific compounds. Acetone is not metabolized in the nose, MMA is metabolized at a moderate rate by nasal tissues, and VA is metabolized at a high rate in mucus and tissues. Equations derived from steady-state analyses show the importance of the specific biochemical and physiological parameters for clearance of each of these chemicals and permit calculation of airstream clearance from simple algebraic relationships.

Penetration of an antibacterial dentine-bonding system into demineralized human root dentine in vitro.

In this study, the penetration of three proprietary dentine-bonding agents (Prime & Bond 2.1, Single Bond, Liner Bond 2) and experimental dentine-bonding systems incorporating an antibacterial monomer, 12-methacryloyloxydodecylpyridinium bromide (MDPB), into artificial root caries lesions was evaluated, and the bactericidal activity of each material against Streptococcus mutans or Lactobacillus casei impregnated into demineralized dentine blocks was assessed. All of the commercial dentine-bonding agents were capable of penetrating into the artificial carious lesions to more than 150 microm. The depth of penetration of the experimental systems, which were based on Liner Bond 2, was not significantly different from that of their parent product. Liner Bond 2 primer exhibited the greatest bactericidal effects among the three proprietary dentine-bonding agents tested. Bactericidal activities of experimental primers containing MDPB were greater than those of any other products, and the application of 4% MDPB-containing primer resulted in complete killing of bacteria in demineralized dentine. The results indicate that the penetration of dentine-bonding agents into extensively demineralized root dentine is possible in vitro, and the experimental dentine-bonding systems containing the antibacterial monomer MDPB are capable of killing bacteria within demineralized dentine. This could be of benefit when managing root caries lesions.