Assessment of iodine-treated filter media for removal and inactivation of MS2 bacteriophage aerosols.

AIMS: To investigate the performance of an iodine-releasing filter medium for use as a protective device against airborne pathogens. METHODS AND RESULTS: The filter's physical and viable removal efficiencies (VRE) were investigated with challenges of MS2 bacteriophage aerosols, and the infectivity of MS2 collected on the filter was analysed. To test a proposed inactivation mechanism, media containing thiosulfate or bovine serum albumin (BSA) were put in impingers to quench and consume I(2) released from the filter. In direct plating experiments, treated filters presented significantly higher VREs than did untreated filters; however, collection in excess BSA decreased VRE by half and in thiosulfate the apparent VRE decreased drastically. No significant difference in infectivity of retained viruses on treated and untreated filters was observed at the same environmental condition. CONCLUSIONS: Evidence presented herein for competition by dissolved I(2) in infectivity assays supports a mechanism of induced displacement and capture of I(2.) It also requires that dissociation of iodine from the filter and capture of iodine by MS2 aerosols as they pass through the filter be factored in the design of the assessment methodology. The filter's strong retention capability minimizes reaerosolization but also makes it difficult to discriminate the antimicrobial effect at the surface. SIGNIFICANCE AND IMPACT OF THE STUDY: This study shows the direct plating assay method to be sensitive to interference by iodine-releasing materials. This requires reevaluation of earlier reports of VRE measurements.

Effect of impactor inlet efficiency on the measurement of wood dust size distribution.

Two designs of cascade impactor inlets were evaluated experimentally to determine their particle sampling differences. One was the standard shrouded inlet provided with the low flow rate (2 L/min) Marple Personal Cascade impactor (Marple). The other was a simple vertical tube used with medium flow rate (15-30 L/min) impactors used as area samplers (e.g., Microorifice Uniform Deposit Impactor, Andersen, Sierra, Berner, or University of Washington [UW] impactor). When two impactors (Marple and UW) were used side-by-side to measure particle size distributions in the wood products industry, they often produced very different size distributions. In the laboratory the particle aspiration efficiencies of both impactor inlets were determined using monodisperse solid particles with aerodynamic diameters (Da) ranging from 5 to 68 microm at wind speeds of 0.55 and 1.1 m/sec. For particles with Da greater than 10 microm, the sample obtained using a simple vertical inlet tube was more representative of the environmental concentration than that obtained using the shielded inlet provided with the Marple impactor. Tests conducted using the Marple impactor inlet without a visor produced aspiration efficiencies that varied with inlet orientation and wind speed. The vertical sampling tube was found to be a better sampler inlet for indoor aerosol sampling.

Evaluation of six inhalable aerosol samplers.

Six inhalable aerosol samplers were evaluated experimentally as area samplers using monodisperse solid particles with aerodynamic diameters ranging from 5 to 68 microm. Sampler performance and inside particle loss at two test wind speeds (0.55 and 1.1 m/sec) and three wind orientations (0, 90, and 180 degrees) were investigated. The six inhalable aerosol samplers tested were a RespiCon, an Institute of Occupational Medicine (IOM), a seven-hole, a conical inhalable sampler, a prototype button sampler, and a closed-face 37-mm cassette. The area sampling performance of the RespiCon sampler matched the inhalable convention fairly well. The sampling performances of the other five samplers depended on wind speed, wind direction, and particle size, and they may not be appropriate for area sampling if the wind speeds are greater than 0.5 m/sec.

An aerosol generator system for inhalation delivery of pharmacologic agents.

Most commercially available aerosol generators widely used in medical applications produce aerosols characterized by a large mass median diameter in the 4-8 micron range and the particle size in the 0.1-10.0 microns range. The desirable size of therapeutic and diagnostic aerosols, however, is about 2-4 microns mass median diameter, and less than 2.0 geometric standard deviation; this size increases the reproducibility of inhalation tests and enhances drug efficacy. We combined the commercially available DeVilbiss Model 65 nebulizer with a dilution/mixing chamber developed in our laboratory. The characteristics of this aerosol generator system were examined over a range of operating conditions and concentrations of solutions of three bronchoconstrictive agents--histamine, carbachol, and methacholine. The aerosol generator system produced a polydispersed aerosol with a mass median diameter range of 1.7-2.4 microns and geometric standard deviation of 1.5. The reliable and reproducible operation of the aerosol generator system greatly increases the power of bronchial challenge tests with bronchoconstrictive drugs.

Sampling of tangential flow streams.

The causes and characteristics of tangential flow in industrial stacks are described. Errors induced by tangential flow in the determination of volumetric flow rate and particulate concentration are analyzed. Experiments were conducted at the outlet of a cyclone collector in order to investigate the effect of tangential flow on the determination of emission rates. Straightening vanes were found to be useful in the reduction of error in flow rate measurements.

Efficiency and loading characteristics of EPA's high-temperature quartz fiber filter media.

It was experimentally demonstrated that Gelman Type A and "Microquartz" filters are efficient collectors of nonvolatile particles at high temperatures. Submicron particles penetrated more than large particles, and most at the highest filtration velocity tested of 51 cm/sec. In all tests, however, aerosol penetration was never more than about 0.10%. Nonvolatile particles penetrated less with increasing temperature filter loading. Particles with vaporization points below the sampling temperature, including H2SO4, can vaporize, pass through the glass fiber filters, and then recondense when cooled below their dew points. Therefore, the definition of "particulate matter" must be based upon a prescribed temperature. Hot stack gases, sampled at different filter temperatures, should not necessarily be comparable. Particulate emission standards must involve a suitable reference temperature to allow proper enforcement. Filtration efficiencies calculated by theoretical equations change dramatically with small changes in assumed average filter fiber diameter and/or particle size (or size distribution) used in the calculations. Pinholes not visible to the naked eye do not appear to effect penetration of glass fiber filters enough to significantly alter stack sampling results. Effect of temperature on filtration of non-volatile particles simply resulted in an increasing collection of submicron particles with increasing temperature. The main problems encountered at elevated temperatures were vaporization of volatile particles and mechanical leakage of the filter holder.

The performance of piezoelectric crystal sensors used to determine aerosol mass concentrations.

Aerosol mass concentration determination using piezoelectric crystal sensors was investigated. Five areas of influence were studied: temperature, humidity, particle collection characteristics, response linearity, and mass sensitivity. A theoretical review is included. Neither air stream temperature nor humidity fluctuations were compensated by the use of a reference crystal. The temperature induced error was satisfactorily reduced by minimizing the inlet temperature change rate. The humidity induced error resulted principally from moisture absorption and desorption by the aerosol deposit. The observed linear response limits ranged from 0.2 to 6 mug/mm2 for various aerosols and instrument designs. No relationship between the linearity limit and the point of complete saturation was apparent. The mass sensitivity was a function of the deposit size and location. Energy trapping theory helped to predict the mass sensitivity distribution. The mass sensing ability decreased for particle sizes beginning at approximately 2 mum diameter, reaching essentially zero at 20 mum. The use of viscous crystal coatings appeared to improve the sensing ability in the 2 to 20 mum size range.