Relationships between composition and pulmonary toxicity of prototype particles from coal combustion and pyrolysis
The hypothesis that health effects associated with coal combustion fly-ash particles are exacerbated by the simultaneous presence of iron and soot was tested through two sets of experiments. The first set created prototype particles from complete and partial combustion, or oxygen free pyrolysis of a high iron Illinois bituminous coal in an externally heated drop-tube furnace. The second experiment created prototype particles consisting of iron and soot in various concentrations from doped ethylene Burke–Schumann flames. Size-classified samples from the coal tests were separated into coarse (>2.5 ?m), fine (0.5–2.5 ?m) and ultrafine (<0.5 ?m) fractions, and analyzed for total carbon, elemental composition, and detailed iron and sulfur speciation. In a similar manner, ultrafine particles from the ethylene flame tests were also analyzed for total carbon and elemental composition. Pulmonary inflammatory responses were determined after intratracheal aspiration of 100 ?g samples in female CD1 mice. IL-6 and neutrophil responses were monitored as markers of inflammation. With carbon present, the coal data suggested that the ultrafine particles containing soot were more toxic than fine or coarse particles containing char, even though the iron and sulfur speciation varied only slightly with particle size. Iron and sulfur chemistry were, however, dependent on the extent of carbon burnout achieved. In the absence of carbon, ultrafine particles (high in bisulfates and semi-volatile alkali metals) were less toxic than the fine fraction (high in oxidized iron and sulfates). Iron-soot particles created from ethylene flames were more toxic than an equivalent physical mixture of iron oxide and soot, and the toxicity depended primarily on the soot concentration. However, taken as whole, these data do not support the notion that iron and soot interact to enhance pulmonary inflammatory responses.