Case 4: Toxicologic and Epidemiologic Clues from the Characterization of the 1952 London Smog Fine Particulate Matter in Archival Autopsy Lung Tissues
Background
Exposure to atmospheric fine particulate matter (PM), even at low ambient concentrations, has clearly been linked to increases in mortality and morbidity. A 10-µg m-3 increase in PM10 (PM <10 µm) has been found to produce a 0.5% increase in daily mortality. The mechanism of action is a source of debate, although recent attention has focused on the cardiac effects of PM exposures. Likewise, several possible etiologic agents have been implicated, including ultrafine PM (PM <100 nm), metals, and the acid components, yet the responsible constituent remains undetermined. During the catastrophic PM exposure episode in London in December 1952, some 4,000 excess deaths occurred at the height of the event. The extreme mortality during that episode and the preservation of archival autopsy tissues allow us the unique opportunity to report on the form and composition of December 1952 London PM in situ in tissues from persons known to have died from the smog exposure. Because absolute increases in mortality with current levels of PM in Western Europe and North America are low, analogous tissues are unlikely to be contemporaneously available.
Materials and Methods
Taking a lung compartment (airway, airspace, interstitium, and lymph node) approach, we differentiated exposures contemporary with death from those of earlier origin.
Results and Discussion
Electron microscopic analyses revealed the dominance of retained ultrafine soot and a surfeit of other particle types. A variety of metal-bearing particle types were found in all compartments, but Pb, Zn, and SnZn types appeared the least biopersistent. The figure (right) consists of a BSE image (a) of macrophages containing innumerable fine PM, and an inset (b) of a high resolution SEM Secondary Electron image showing aggregates of Ultrafine PM. These carbonaceous aggregates of Ultrafine PM may have originated from Diesel engines as well as coal burning activities. Magnification bar marker in a = 1 µm, in b = 500 nm. See also Ultrafine Particles in Air Pollution.
Conclusioin
The results support the ongoing investigations of the acute toxicologic importance of fine and ultrafine carbonaceous and metal PM. These also reinforce the historical importance of the phasing out of electric trams in London in 1952 and their replacement by thousands of diesel buses.
This study was supported by funding from the American Lung Association Clinical Investigator Award CG-016-N and from the Department of Pathology at Upstate Medical University.
