Influence of relative humidity on particle size and UV sensitivity of Serratia marcescens and Mycobacterium bovis BCG aerosols.

SETTING: A study of Serratia marcescens and BCG aerosols. OBJECTIVE: To evaluate the effect of relative humidity (RH) on (1) the particle size and (2) sensitivity of 254nm germicidal ultraviolet (UV) irradiation. METHODS: We built a RH controlled experimental chamber into which bacteria were aerosolized, exposed to varying amounts of UV irradiance over measured time periods, and quantitatively evaluated for viability. Aerosolized Serratia marcescens and bacille Calmette-Guérin (BCG) were subject to UV doses ranging from 57-829 microW. sec/cm(2), and sampled with a six-stage Andersen culture plate impactor at RHs ranging from 25-95%. RESULTS: Percent survival for both organisms was inversely related to UV dose. Serratia marcescens was more susceptible to UV than BCG under all conditions. More than 95% of the bacterial aerosol particles were 1.1-4.7 microm in aerodynamic diameter, and particles sizes increased from low (25-36%) to high (85-95%) RH. The count median diameter ranged from 1.9-2.6 microm for Serratia marcescens and from 2.2-2.7 microm for BCG as RH increased. For both Serratia marcescens and BCG, resistance to UV increased as RH increased. The UV resistance of both Serratia marcescens and BCG aerosols dramatically increased at RH higher than 85%. CONCLUSIONS: Our results indicate that differences in UV dose, kinds of microorganisms, airborne particle size and RH affect UV susceptibility.

Marijuana and tobacco smoke gas-phase cytotoxins.

To evaluate the in vivo versus in vitro paradoxical effects of marijuana and tobacco smoke on pulmonary defenses, the responses to smoke constituents were assessed with an alveolar macrophage tissue culture bioassay. A dose-response impairment of macrophage bactericidal activity was associated with water-soluble, gas-phase constituents. A model airway surface was constructed to examine the behavior of specific gas-phase constituents removed as they passed over wetted surfaces simulating the characteristics of the human respiratory system. Chemical analyses in the bioassay flask and in the model airway were compared. Gas-phase cytotoxins were measured after passage over wetted surface areas analogous to the trachea between the larynx and second-order bronchus. A wetted surface comparable to only 5% of the human airway, or less than 0.05% of the gas-exchanging surface of the entire lung, was capable of complete detoxification of the highly water-soluble gas-phase cytotoxins. In conclusion, gas-phase cytotoxins demonstrable by in vitro bioassays may have no cytotoxic potential when inhaled by humans.

Effects of airflow rates and operator activity on containment of bacterial aerosols in a class II safety cabinet.

Biological safety cabinets are frequently relied upon to provide sterile work environments in which hazardous microorganisms can be safely handled. Verification of correct airstream velocities does not, by itself, ensure that adequate protection will be achieved under all users. Instead, the concentration of microorganisms in a cabinet operator's breathing zone must be measured during typical cabinet use conditions to determine whether the exposure is below acceptable limits. In this study, cabinet operator exposures were measured with a personal air sampler. Bacterial spores were released inside a cabinet as a uniform challenge aerosol, and the number of escaping spores was measured for several cabinet arrangements during a number of typical operations. The following were studied to determine their effects on aerosol containment: inflow air velocity, size of access opening, type of operator movements, location of operator's hands, and pace of activity. Other experiments examined differences in aerosol containment for eight typical microbiology operations when performed by six operators who covered a range of body heights and volumes.

Personal air samplers for measuring occupational exposures to biological hazards.

Microbiological air samplers, designed to be worn as personal samplers, were evaluated for studying occupational exposures to aerosols of infectious and allergenic materials. Gelatin filter media, an impinger sampler, and spiral and cascade impactors were tested for collection efficiency for small (less than or equal to 2 microns) latex spheres and for recovery of bacterial aerosols. Only 20% of an aerosol of 0.8 micron latex particles passed through the impinger uncollected, while recovery of bacteria equalled or exceeded collection in an all-glass impinger. Gelatin filters matched the collection efficiency of membrane filters, but were unsatisfactory for the isolation of bacteria sensitive to dehydration. The spiral sampler and the cascade impactor provide information on the size distribution of collected particles, although, at present, collection efficiencies for very small particles are too low for rigorously quantitative studies. Methods of collection, and sampling strategies for biological aerosols are similar to those used for measuring exposures of workers to chemical and mineral aerosols; however, preparation of samples and identification of isolates may have to be referred to experts in the fields of bacteriology, virology, and mycology.

Storage cabinet for volatile toxic chemicals.

It is common practice to store toxic volatile chemicals in a laboratory fume hood. Although this provides safe storage, it becomes necessary to operate the hood continuously, resulting in a continuous loss of conditioned air from the building. Often, bottles containing highly toxic chemicals are few in numbers and small in size so that the storage volume required for this purpose is modest. This makes it possible to utilize a small auxiliary storage cabinet in place of a chemical hood for this purpose, provided all the vapors from the stored chemicals can be retained. We have constructed and tested a passive storage cabinet consisting of a metal box, 30 X 30 X 30 cm, with a front-opening latchable door, a false bottom for catching and retaining liquid spills, and an open top completely covered with a 5-cm depth of tightly packed, gas-adsorbing, activated charcoal. All vapors released inside the cabinet must pass through the charcoal before reaching the outside and are retained on the charcoal. Means are provided to purge the box of residual vapors before opening the door by compressed air line or a hand-operated squeeze bulb. The incoming fresh air sweeps through the chamber and exists through the charcoal filter.

Effect of plateout, air motion and dust removal on radon decay product concentration in a simulated residence.

The effectiveness of increased air motion and dust removal in reducing radon decay product concentration in residences subject to radon intrusion was evaluated in a 78-m3 room under steady-state conditions for air infiltration rates between 0.2 and 0.9 air changes per hour. Room-size, portable electrostatic precipitators and high-efficiency fibrous filters were tested as typical residential air cleaning devices; a portable box fan and a ceiling fan were employed as typical residential air movers. Reductions in working levels of 40-90% were found. The fate of radon decay products, with and without mixing fans, was determined by direct measurement. When mixing fans were used, most of the nonairborne potential alpha-energy was plated out on the room surfaces; less than 10% was deposited on the fan blades or housing. Results were compared to a mathematical model based on well-mixed room air, and good agreement was obtained.

Reuter centrifugal air sampler: measurement of effective airflow rate and collection efficiency.

Incorrect calculation of effective air sampling rate and disregard of differences in collection efficiency among samplers can lead to false conclusions about the usefulness of samplers for measuring concentrations of airborne microorganisms.

A method for measuring respiratory deposition of cigarette smoke during smoking.

An understanding of the factors influencing respiratory deposition of cigarette smoke in smokers is needed to accurately control this important source of respiratory exposure in epidemiological studies of workers. Only a few studies have characterized the deposition of cigarette smoke in smokers and these involve methods that interfere with normal smoking. A technique for measuring puff volume, inhaled amount, and respiratory deposition of cigarette smoke particulate phase has been developed. It provides satisfactory accuracy (+/- 10%) and causes minimal disruption of normal smoking pattern. The technique captures exhaled smoke with an exhaust hood and establishes the amount of inhaled smoke by monitoring puff volume, puff duration, and puff timing and replaying the exact smoking sequence with matched cigarettes. Mass of captured cigarette smoke is evaluated by fluorophotometry. Preliminary trials with 11 paid volunteers gave an average puff volume of 53 mL and smoke deposition ranged from 22% to 75% with an average of 47%. Measured depositions are lower than previously published values and higher than would be predicted for submicrometer sized particles during normal breathing.

Marijuana, tetrahydrocannabinol, and pulmonary antibacterial defenses.

Although marijuana is now consumed extensively, little is known of its biologic effects on the lung. To study this problem, the intrapulmonary inactivation of an aerosolized challenge of Staphylococcus aureus was quantified in rats exposed to graded amounts of fresh marijuana smoke. Controls inactivated 85.1 percent +/- 0.3 percent of the bacteria six hours after inoculation. Following an in vivo accumulative exposure to smoke from progressively increasing numbers of marijuana cigarettes for periods of ten minutes each hour for five consecutive hours, intrapulmonary bacterial inactivation was impaired in a dose-dependent manner. Evaluation of the effects of parenterally administered delta-9-tetrahydrocannabinol (THC) or of exposure to fresh smoke from THC-extracted marijuana placebo cigarettes indicated that the cytotoxin in marijuana was not related to the primary psychomimetic component. Thus, marijuana smoke is toxic to the lung and impairs the pulmonary antibacterial defense system in a dose-dependent manner.

Uncertainty in particle counting and sizing procedures.

A method is described for calculating confidence intervals for particle or fiber concentration, and for dust collector penetration. The span of the interval depends upon the value of fiber concentration or collector penetration reported and upon the number of particles or fibres counted.