On inhalation health effects of combustion generated ash aerosol particles

Abstract

Epidemiological studies have consistently shown an association between elevated quantities of ambient airborne particulate matter (PM) and acute health effects. The focus here is on health effects of primary PM and is intended to provide insight into the roles of particulate speciation on inhalation toxicity. PM considered consisted of combustion generated ash particles from (1) coal, (2) coal/municipal sewage sludge (MSS) mixture, (3) MSS burned with natural gas assist, (4) coal/refuse derived fuel (unstaged and staged), (5) residual fuel oil (ROFA), (6) combustion generated zinc particles, with and without sulfur, and (7) combustion generated zinc which had been sequestered by sorbent particles. In each case, health effects were investigated in-vivo by direct inhalation by a mouse model. An aerosol re-suspension system that produces aerosol concentrations of ∼1000μg/m³ was designed, and characterized. Particles were characterized with respect to size, elemental composition, leachability, and pH of supernatant. Measured alterations in lung permeability, along with pulmonary functions were used as measurements of lung injury. One-hour exposures were conducted for periods lasting from 1 to 24 days. The validity of assumptions used in the lung permeability measurement technique, was explored using a new mathematical model. In-vivo results indicate two types of lung permeability behavior. Inhalation of ash particles from coal, MSS, residual fuel oil, ZnO, and Zn sequestered by kaolinite caused an initial decrease in lung permeability followed by a "recovery" to control mice values (Type 1 behavior). In contrast, the exposure to ash from coal plus MSS, coal plus RDF, and zinc plus sulfur, triggered an increase in lung permeability (Type 2 behavior). This work demonstrates the value of health effects engineering, combining both combustion engineering and toxicology. Particle speciation is extremely important and sulfated zinc has been identified as a "bad actor". Ash aerosol from either coal or MSS combustion alone produces Type 1 behavior in lung permeability, while ash aerosol from combustion of a mixture of coal and MSS produces Type 2 behavior. The high temperature capture of zinc vapor on kaolinite sorbent greatly mitigates lung injury allowing permeability behaviors to change from Type 2 to Type 1.