Biological incinerator emissions of toxic inorganics, their residues and their availability

Abstract

Air particulate emissions from incinerators and the residual solids remaining as fly ash and bottom ash have been characterized physically and chemically to examine trace and minor elements and their speciation by a combination of radioanalytical, SEM and radiotracer techniques. Repeated (n= 25 and 35), size-selective sampling of airborne particulate matter downwind from medical and sewage sludge incinerators in Toronto was performed and the results were confirmed by direct analysis of stack fly ash. It was found that Ag, Cd, Cl, Cr, Sb and Zn are consistently elevated in hospital biomedical incinerator emissions and As, Br, I and Se in sewage incinerators; these elements were significantly elevated in respirable particles of submicron sizes, as also is environmental Pb. Concentration patterns of these five to six strongly correlated elements serve as a ‘signature’ of incinerator emissions and also are used to quantify the fraction of local respirable aerosol due to incineration. The fidelity of particle-size separation and classification by cascade impactors was directly verified by (i) direct particle-size measurement, stage-by-stage using SEM, and (ii) indirectly, by observing log-normal size distributions over the range 0.2–7 µm, distributions known to be characteristic of random aerosols. Since the bioavailability of toxic trace elements, either as enriched particulate emissions or as result of incinerator residue placed in landfill disposal sites, depends on their relative solubility by lung fluids and/or ambient rainfall or groundwaters, several air filters and ash samples were subjected to controlled leachability tests. Variable fractions of trace elements (about 0–50%) on air filters and in ash were solubilized under simulated, realistic leaching conditions (pH 4–5), particularly halides, cadmium, chromium and zinc. This indicates a vaporization/condensation model of incineration and surface loadings of incineration particles with chloro-complexes and other simple cations.