The most dangerous products of incineration are tiny, invisible, pollutioncoated particles released into the atmosphere. In the air pollution business, these are known as "fine particles." Despite the best available control technology, incinerators emit large quantities of such particles, which typically measure two micrometers or less in diameter. A micrometer is a millionth of a meter and a meter is 39 inches. Pollution control devices like Venturi scrubbers and baghouse filters are not very efficient at trapping these small particles, so to save money for incinerator operators (and thus encourage incineration, which is the stated goal of the EPA), the U.S. Environmental Protection Agency has declared it "OK" for incinerators to emit large quantities of the smallest particles. Federal law says that an incinerator is allowed to emit 180 milligrams of particles with each cubic meter of air (or 0.08 grains with each cubic foot of air). There are 437.5 grains in an ounce. One large incinerator smoke stack may emit 100,000 cubic feet of air every minute, day in and day out, or 52 billion cubic feet per year. It would be legal for such an incinerator to emit 300 tons of particles yearly. Typically, half of these particles will measure 2 micrometers or less in diameter and thus will be "respirable," which means that you and I can breathe them into the very bottom of our lungs because nature has provided us with no defense against particles this small. From our lungs, they can pass directly into our blood. (See RHWN #131, where we discussed the penetration of these fine particles into human lungs.)
The National Academy of Sciences, in AIRBORNE PARTICLES (Baltimore: University Park Press, 1979), discussed the health dangers of fine particles from many points of view. The "background level" of these fine particles in uninhabited regions of Canada is 1 to 3 micrograms in each cubic meter of air; in the rural Midwest, you'll find 5 to 12 micrograms in each cubic meter of air. This is not a "natural" background level; it represents pollution created by humans. Nevertheless, this background level is a good standard against which to judge the allowable emission of particles from incinerators. The allowable emissions from an incinerator exceed background concentrations by anywhere from a factor of 15,000 to a factor of 180,000. The EPA is relying upon dilution to protect you. They will argue that, by the time those particles reach your lungs, they will be diluted in a lot of fresh air and thus won't be quite so far above background levels when you breathe them. But this, of course, depends upon how close you live to an incinerator, how the wind currents go, whether there are thermal inversion conditions in your local atmosphere, and so forth. There is growing evidence (to be presented next week) that the EPA's dilution strategy isn't safe.
Fine particles remain airborne for long periods of time, and before they fall to earth they can travel several hundred miles or even farther. They can present a danger to humans all along their route. Fine particles weigh so little that they do not respond predictably to the pull of gravity. The smallest air current keeps them aloft. These particles are so small that rain drops do not wash them from the atmosphere. You are no doubt familiar with the force of air being pushed ahead of a truck barreling down the highway; it gives your car a push as it goes by. In the same way, raindrops (which measure 500 to 9000 micrometers in diameter) push air ahead of them as they fall, and they knock fine particles aside instead of washing them to earth.
Increasing the concentration of fine particles in the atmosphere is not good for people. Hardest hit are those with bronchitis and asthma, those who are very young or old, and those who exercise outdoors. Breathing through your mouth (which is one of the first things people do when they exercise, play sports, or jog) increases the intake of fine particles into the lungs. In addition, some healthy people absorb 50% more fine particles into their lungs than the average. The reasons for this are not understood. One particularly important aspect of fine particles is that they carry into our lungs pollutants that could not otherwise get there. In this sense, fine particles have synergistic (multiplier) effects with other pollutants. The Academy said, "The generally accepted view of synergism extends beyond potentiation [increasing a pollutant's power] to include the role of toxic vector [carrier]. Such gases as sulfur dioxide are probably either adsorbed to the particulate surface or absorbed into the particles, and thereby transported into the alveolar regions [in the deep lung], where they exist in high, localized concentrations. These localized high concentrations [in the lung] could not be produced without particles. Accordingly, sulfur dioxide sorption to particulate matter might effectively allow sulfur dioxide penetration into the alveolar regions at even nominal environmental concentrations of the gaseous pollutant." In other words, "normal" or "acceptable" levels of sulfur dioxide may be made dangerous by the presence of fine particles.
"In summary," said the National Academy, "particulate atmospheric
pollutants may be involved in chronic lung disease pathogenesis
as causal factors in chronic bronchitis, as predisposing factors
to acute bacterial and viral bronchitis, especially in children
and cigarette smokers, and as aggravating factors for acute
bronchial asthma and the terminal stages of oxygen deficiency
(hypoxia) associated with chronic bronchitis and/or emphysema and
its characteristic form of heart failure (cor pulmonale)."
--Peter Montague, Ph.D.
Descriptor terms: lung disease; particulates; air pollution; air quality; canada; bronchitis; emphysema