Urban aerosol toxicity: the influence of particle size.

The basic thesis developed herein is that particle size is an extremely important parameter to consider when assessing the potential toxicity of species present in urban aerosols, and that surface adsorption or condensation greatly promotes toxicity. In the majority of cases this means that particles that are less than 1 micro.m in size are of primary importance. Special significance is attached to the organic constitutents of aerosols. Many of these are known or potential carcinogens and most predominate in extremely small particles which become deposited almost exclusively in the lung.

Toxic trace elements: preferential concentration in respirable particles.

The toxic trace elements arsenic, antimony, cadmium, lead, selenium, and thallium were found to be most concentrated in the smallest respirable particles emitted from coal-fired power plants. These elements, or their compounds, are probably volatilized during combustion and preferentially adsorb or condense onto the small particles which can most easily pass through conventional control equipment.

Oxidative transformations of polycyclic aromatic hydrocarbons adsorbed on coal fly ash.

Polycyclic aromatic hydrocarbons adsorbed onto coal fly ash were found to be stabilized against photochemical decomposition. However, a number of adsorbed polycyclic aromatic hydrocarbons will spontaneously oxidize in the absence of light, with those compounds containing a benzylic carbon being particularly susceptible. The decomposition rate appears to be fly ash-dependent.

Surface predominance of trace elements in airborne particles.

A number of minor and trace elements including Be, C, Ca, Cr, K, Li, Mn, Na, P, Pb, S, Tl, V, and Zn present in coal fly ash are found to be preferentially concentrated on the particle surfaces. Environmentally effective concentrations of these elements are thus much higher than indicated by conventional bulk analyses.

Potentially carcinogenic species emitted to the atmosphere by fossil-fueled power plants.

The identities and physicochemical characteristics of potentially carcinogenic species emitted to the atmosphere by fossil-fueled power plants are presented and discussed. It is pointed out that many so-called carcinogens are preferentially concentrated on the surface of respirable fly ash particles thus enabling them to come into intimate contact with lung tissues when inhaled. Relatively little information is available about the identities of particulate polycyclic organic compounds whose emission from coal fired power plants may well be substantially greater than hitherto supposed. The importance of chemical changes, which several species may undergo following emission (but prior to inhalation) in determining their potential carcinogenic impact, is stressed.