Surface Area, Adsorption, and Desorption Studies on Indoor Dust Samples

Abstract

Adsorption by dust samples from homes was studied to evaluate the extent to which household dust particles could act as carriers of vapors into the lower respiratory tract. The dust samples were examined for volatilizable and combustible materials via thermogravimetric analysis as well as for specific surface area and surface characteristics by nitrogen and formaldehyde adsorption and desorption isotherms. Particle morphology and size were examined by scanning electron microscopy (SEM) and elemental composition by energy dispersive x-ray analysis (EDX A). Thermogravimetric analysis (TGA) demonstrated marked differences between samples from different homes. The volatilizable material removed by heating dust samples in argon to 500° C ranged from 32% to 69%. The residue not combustible in oxygen at 700° C, presumably minerals, ranged from 11% to 58%. In most cases, differences between samples from the same home were small. SEM of the samples demonstrated the presence of many fibers and of irregularly shaped particles, usually less than 10-µ projected diameter. The fibers were combustible. Particle-by-particle analysis by EDXA demonstrated that samples were heterogenous. Many particles contained Si, Al, Mg, and Ca, elements which are characteristic tracers of windblown soil/dust. The range of specific surface areas measured by nitrogen adsorption after heat treatment at 50° C was quite small, 0.7 to 1.6 m2/g. An increase in specific surface area with temperature of pretreatment (outgassing temperature) was observed, suggesting that the surface of the particles was covered by adsorbed water or other vapors. No major differences in specific surface areas of samples collected from different homes, or collected from the same home in different years, were observed. The formaldehyde isotherms showed marked hysteresis, suggesting either porosity of the dusts or chemisorption. The desorption of formaldehyde was slow, suggesting that vapors adsorbed onto room dust samples remain associated with particles for several days after adsorption. These findings indicate that organic vapors that are adsorbed to inhaled room dust may be deposited in the deep lung along with the particles and may be available to interact with lung cells. © 1989, Taylor & Francis Group, LLC. All rights reserved.