Sidney C. Soderholm

Increased pulmonary toxicity of ultrafine particles? I. Particle clearance, translocation, morphology

The purpose of our studies is to elucidate the basic mechanism of lung tissue injury which may be common for particles of high or low toxicity. In experiments on rats we compared particle translocation of two types of TiO 2 and of two types of Al 2 O 3 . The types of TiO 2 or Al 2 O 3 differ in origin, manufacturing technology and most importantly in the size of the primary particles, but not in chemical or crystallographic characteristics

Estimation of the times for evaporation of pure water droplets and for stabilization of salt solution particles

Abstract The evaporation or stabilization times of isolated pure water and salt solution particles were calculated with a previously published theory [Ferron, G. A. (1977) J. Aerosol Sci.8, 265] and other theories available in the literature. The calculated life times were most sensitive to the value of the water accommodation coefficient αw. Comparing calculated life times for αw = 0.04 and 1.0, the differences are within a factor of 2 for particles with a size of 10 μm and within a factor of 6 for particles with a size of 1 μm. The evaporation times of pure water particles were calculated for a temperature of 20°C and several relative humidities of the air, and the results were approximated by simple mathematical equations. These equations were extended for air temperatures between 0 and 50°C. The stabilization time of a salt solution particle for evaporation is well estimated by the life time of a pure water particle with the same size in air at the same temperature and relative humidity. Differences larger than a factor of two are found for particles containing a high salt concentration with a relative humidity in air near to the relative humidity of the saturated salt solution. The stabilization time for condensation of water on a dry salt particle as characterized by the time to reach 95% of the maximal increase in particle size is well estimated by the life time of a pure water particle with an initial diameter equal to the equilibrium diameter of the salt solution particle in the air.

Aerosol Sampling Efficiency of 37 mm Filter Cassettes

This research compared the sampling efficiencies of open- and closed-face 37 mm filter cassettes and an experimental cassette with a tapered inlet. The experiment involved challenging the cassettes with various aerosol sizes up to 24 micron Mass Median Aerodynamic Diameter (MMAD) in a wind tunnel operated at 100 cm/sec. Sampling efficiencies were determined by comparing cassette mass concentration measurements to paired isokinetic samples. It was found that sampling efficiencies dropped with increasing particle size and that the cassette with the tapered entry offered no improvement to sampling efficiency. Sampling efficiency appeared to be improved by placing cassettes on a manikin to simulate personal sampling.

Analysis of diffusion battery data

Abstract A brief review is given of the use of diffusion batteries to obtain size information about ultrafine aerosol particles. Accurate formulas are included for the penetration functions of circular tube and parallel plate diffusion cells. After noting the usefulness of some previously suggested data inversion techniques, a new method for obtaining a “complete solution”, is outlined. The techniques are illustrated by the analysis of some experimental data.

Rationale and Recommendations for Particle Size-Selective Sampling in the Workplace

Abstract Because many aerosol hazards depend upon particle size, the American Conference of Governmental Industrial Hygienists established an Air Sampling Procedures Committee to “recommend size-selective aerosol sampling procedures which will permit reliable collection of aerosol fractions which can be expected to be available for deposition in the various major subregions of the human respiratory tract.” After reviewing available data on regional deposition of inhaled particles and on the collection efficiencies of sampling instruments, the committee recommends use of three particulate mass fractions for workplace sampling: inspirable particulate mass (IPM), for materials which may be hazardous anywhere in the respiratory tract; thoracic particulate mass (TPM), for materials which may be hazardous anywhere within the lung airways and the gas exchange region; and respirable particulate mass (RPM), for materials which may be hazardous in the gas exchange region of the lung. The mass fractions are defined ...

Thermal degradation events as health hazards: Particle vs gas phase effects, mechanistic studies with particles

Exposure to thermal degradation products arising from fire or smoke could be a major concern for manned space missions. Severe acute lung damage has been reported in people after accidental exposure to fumes from plastic materials, and animal studies revealed the extremely high toxicity of freshly generated fumes whereas a decrease in toxicity of aged fumes has been found. This and the fact that toxicity of the freshly generated fumes can be prevented with filters raises the question whether the toxicity may be due to the particulate rather than the gas phase components of the thermodegradation products. Indeed, results from recent studies implicate ultrafine particles (particle diameter in the nm range) as potential severe pulmonary toxicants. We have conducted a number of in vivo (inhalation and instillation studies in rats) and in vitro studies to test the hypothesis that ultrafine particles possess an increased potential to injure the lung compared to larger-sized particles. We used as surrogate particles ultrafine TiO2 particles (12 and 20 nm diameter). Results in exposed rats showed that the ultrafine TiO2 particles not only induce a greater acute inflammatory reaction in the lung than larger-sized TiO2 particles, but can also lead to persistent chronic effects, as indicated by an adverse effect on alveolar macrophage mediated clearance function of particles. Release of mediators from alveolar macrophages during phagocytosis of the ultrafine particles and an increased access of the ultrafine particles to the pulmonary interstitium are likely factors contributing to their pulmonary toxicity. In vitro studies with lung cells (alveolar macrophages) showed, in addition, that ultrafine TiO2 particles have a greater potential to induce cytokines than larger-sized particles. We conclude from our present studies that ultrafine particles have a significant potential to injure the lung and that their occurrence in thermal degradation events can play a major role in the highly acute toxicity of fumes. Future studies will include adsorption of typical gas phase components (HCl, HF) on surrogate particles to differentiate between gas and particle phase effects and to perform mechanistic studies aimed at introducing therapeutic/preventive measures. These studies will be complemented by a comparison with actual thermal degradation products.

Some Chemicals Requiring Special Consideration when Deciding Whether to Sample the Particle, Vapor, or Both Phases of an Atmosphere

Abstract When preparing to measure the concentration of a contaminant in air, a decision must be made whether to sample the particle phase, the vapor phase, or both. The choice to sample only the particle phase or only the vapor phase seems obvious for many contaminants due to their extremely high or low vapor pressures. This work identifies some chemicals that are likely to occur in both the vapor and particle phases in some atmospheres and identifies others for which readily available information may be inadequate or misleading. The saturated vapor concentration (SVC) of numerous chemical substances was calculated from vapor pressure information given in the Documentation of the Threshold Limit Values and Biological Exposure Indices published by the American Conference of Governmental Industrial Hygienists (ACGIH). The results were used to calculate the ratio of SVC to the threshold limit value (TLV) for each substance. Forty-one substances that had a TLV listed only in mg/m3 were found to have a SVC gr...

Perinatal methanol exposure in the rat. I. Blood methanol concentration and neural cell adhesion molecules.

Although the acute toxicity of methanol is well documented, few studies have addressed the consequences of perinatal exposures to the low concentrations that are expected to arise from its proposed use as a component of automobile fuel. This report describes the general research design of a series of studies, the effects of methanol exposures on blood concentrations in dams and neonates, and indices of brain development. Four cohorts of Long-Evans pregnant rats, each cohort consisting of an exposure (n = 12) and a control (n = 12) group, were exposed whole-body to 4500 ppm methanol vapor or air for 6 hr daily beginning on Gestation Day 6. Both dams and pups were then exposed through Postnatal Day 21 (PND 21). Blood methanol concentrations determined by gas chromatography from samples obtained immediately following a 6-hr exposure reached approximately 500-800 micrograms/ml in the dams during gestation and lactation. Average concentrations for pups attained levels about twice those of the dams. Selected offspring from Cohort 4 were exposed for one additional 6-hr session at ages that extended out to PND 52. Regression analyses showed that the blood methanol concentrations of the pups declined until about PND 48, at which time their levels approximated those of their dams. Such pharmacokinetic differences might increase the risks posed to developing organisms. Light-microscopic analysis showed no significant abnormalities in the brains of the methanol-treated animals. However, assays of neural cell adhesion molecules (NCAMs) in brains of pups sacrificed on PND 4 showed staining for both the 140 and the 180 kDa isoforms to be less intense in the cerebellum of exposed animals. NCAM differences were not apparent in animals sacrificed 15 months after their final exposure.

Estimating effects of evaporation and condensation on volatile aerosols during inhalation exposures

Abstract Evaporation and condensation can have significant effects on aerosols in inhalation exposure systems. A detailed mathematical model is presented. It is applicable to monodisperse particles and can accommodate materials which are not completely miscible in water. Simplified equations derived from the model provide insight into the equilibrium state of a system and the characteristic times of its dynamics. The characteristic time of transport of most of a particles mass by evaporation and condensation is proportional to the square of the particle diameter and inversely proportional to the materials saturated vapor concentration. When compared to the results obtained from the detailed mathematical model, predictions of the simplified equations are shown to give valuable insight into the types of changes which occur and their time-scales. Important factors in determining whether significant evaporation and condensation will occur in a system are the ratio of the total airborne concentration to the saturated vapor concentration, the saturated vapor concentration, particle size, the presence of water, the presence of water soluble nonvolatile components, and miscibility with water.

Method of measuring the total deposition efficiency of volatile aerosols in humans

Abstract An exposure system was developed to measure the total deposition efficiency of airborne contaminants which may exist in the vapor, particle, or both phases of an inhaled atmosphere. A formula was derived to account for both deposition in the mouthpiece and one-way valve assembly and the volume of the assembly in the calculation of the total deposition efficiency. A human subject was exposed by mouth to three atmospheres containing either glycerol droplets with accompanying vapor, corn oil droplets of a similar size, or propylene glycol vapor. Analyses of the amounts of the exposure materials collected from a sample of the exposure air, collected from the exhaled air, and recovered from the mouthpiece provided the following average total deposition efficiencies: polydisperse 1 μm glycerol droplets and accompanying vapor 62%, polydisperse 0.8 μm corn oil droplets 19%, and propylene glycol vapor 100%. These experiments demonstrate that the total deposition efficiency of inhaled contaminants in both the particulate and vapor phases can be measured. Variations of deposition efficiency with type of material and aerosol mass concentration are discussed.