=======================Electronic Edition========================
RACHEL’S HAZARDOUS WASTE NEWS #131
—May 30, 1989—
News and resources for environmental justice.
——
Environmental Research Foundation
P.O. Box 5036, Annapolis, MD 21403
Fax (410) 263-8944; Internet: erf@igc.apc.org
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FINE PARTICLES–PART 1: THE DANGERS OF INCINERATION.
Incineration of anything, including garbage and hazardous
chemical wastes, produces a kind of pollution that is uniquely
dangerous to humans: fine particles.
In this series, we will first discuss the characteristics of fine
particles, and later we will discuss health studies showing the
consequences of breathing fine particles.
The process of incineration turns solids and liquids partly into
gases and partly into tiny particles of soot or ash. As the gases
rise in the smoke stack, they cool and some of the gas molecules
come together to form additional fine particles. The resulting
particles are exceedingly small when they are emitted into the
environment. Scientists who study particles make a distinction
between coarse (large) particles and fine (small) particles. Fine
particles behave entirely differently from coarse particles and,
as we will see, are much more dangerous to humans. Fine particles
are also much more difficult and expensive to control. They are
also invisible, so when they are not controlled, there is no way
to know it except by monitoring with the proper instruments.
Coarse particles are those with a diameter larger than 2
micrometers (micrometers); fine particles are those with a
diameter less than 2 micrometers. A micrometer (micrometers) is a
millionth of a meter and a meter is about a yard. (An older term
for micrometer is micron.)
Incinerators emit large numbers of particles, despite the best
available control technology. Half of all the particles emitted
will have a diameter less that 2 micrometers, and the majority of
these will have a diameter of 0.3 micrometers.
It is difficult to imagine how small these particles are. To help
understand what we’re talking about, look at the dot over the
letter i in this newsletter; that dot measures about 400
micrometers in diameter. You can fit 40,000 particles with a
diameter of 2 micrometers on the dot. When the particles have a
diameter of 0.3 micrometers, you can fit 1.7 million particles on
the dot over the i.
Unfortunately, U.S. EPA [Environmental Protection Agency]
regulations do not take into consideration the sizes of the
particles emitted by an incinerator. For regulatory purposes,
coarse particles are considered to be the same as fine particles,
as if they were all equivalent. The regulations issued as part of
the Resource Conservation and Recovery Act (RCRA) allow the
emission of 0.08 grains per dry standard cubic foot of stack gas
(or 180 milligrams per dry standard cubic meter). There are 437.5
grains in an ounce. Measurements show that half these particles
will have diameters ranging from 2.5 down to 0.1 micrometers; of
that half, a majority will have a diameter of 0.3 micrometers. If
we assume that 25% are 2 micrometers, 25% are 1 micrometers, 35%
are 0.3 micrometers and 15% are 0.1 micrometers in diameter, we
can generalize about the fine particle emissions from an
incinerator.
Each pound of fine particles emitted from an incinerator will
consist of 140 quadrillion (1.4 x 1017) individual particles. A
quadrillion is 1000 trillion. Over a year’s time, an incinerator
meeting the federal standards will legally emit anywhere from 10
to 1000 tons of fine particles, depending upon the size of the
incinerator.
Breaking things into fine particles has the effect of vastly
increasing their surface area. A single lump of waste weighing a
pound (and having the same density as water) would have a surface
area of about 44 square inches (a square 6.5″ on a side), about
the size of a large post card. But when that same pound is broken
into fine particles, its combined surface area grows to 9900
square yards (approximately two football fields). This is
important for several reasons: as these fine particles move
upward in the smoke stack, they are immersed in a bath of gaseous
chemicals that are cooling and are “looking” for a place to turn
from a gaseous to a solid state. Fine particles, with their large
surface area, provide an inviting place and so the surfaces of
fine particles become covered with pollutants (“enriched” is the
technical term for this) before they are released into the local
air. In particular, fine particles become coated with toxic
metals (lead, cadmium, arsenic, chromium, and zinc, and with
sulfur and polycyclic aromatic hydrocarbons–or with whatever
else is in the smoke stack).
As the human body evolved throughout its long history, it adapted
to the environment. One factor in the environment has always been
dust, principally from dust storms. Dust from storms is larger
than 5 micrometers in diameter and the human body evolved
mechanisms for protection against such large particles. The hairs
inside the nose, the mucous membranes lining the nose, throat and
lungs, and even the shape of the throat, help to trap dust. As
air is inhaled, the shape of the throat causes the air to swirl,
so heavy dust particles are thrown outward by centrifugal force,
where they strike the mucous-lined walls. As the tubes and
passageways leading to the lungs twist and branch, they provide
many opportunities for particles to collide with sticky walls and
become trapped before they enter the lungs. Once trapped by
mucous, coarse particles are coughed up and excreted.
Nature has gone to great lengths to protect the lungs because the
deepest regions of our lungs provide places (called alveolar
sacs, or alveoli) where oxygen passes into the blood and carbon
dioxide passes out of the blood. The lungs provide a large
surface area for contact with air, and thus with fine particles;
the surface area of the alveoli is 65 square yards, which is
larger than two tennis courts.
Thus, the deep regions of the lung provide very efficient, direct
access to the blood stream and, by this means, to every part of
the body. Unfortunately, humans now produce huge numbers of fine
particles, and these are not caught by the body’s protective
mechanisms–they are simply too small. Fine particles pass easily
into the deepest regions of the lungs, the alveoli, or alveolar
sacs. There they remain indefinitely because no clearance
mechanisms effectively remove them. Nature did not protect us
against such particles, because none existed until very recently.
Once lodged in the deep regions of the lung, fine particles, with
their enormous surface area enriched with toxics, provide a
particularly efficient means for delivering metals and organic
pollutants directly into the blood stream. Their large surface
area provides effective contact with moist tissue and the
opportunity for dissolving or for other chemical reactions,
putting pollutants directly into the victim’s blood. Once in the
circulatory system, toxics are then distributed throughout the
body.
Fine particles have one other characteristic worthy of mention.
They remain airborne for long periods of time and travel long
distances–hundreds of miles, or ever farther. This occurs
because they are so small and light that gravity does not pull
them downward efficiently, so the slightest air current holds
them aloft.
Furthermore, as we shall see, they are not removed from the
atmosphere efficiently by rain. Therefore, for a long time after
they are released into the environment, they remain available for
humans to breathe in. [To be continued.]
The best books on fine particles are those of the National
Research Council, National Academy of Sciences: AIRBORNE
PARTICLES (Baltimore, Md: University Park Press, 1979) and
CONTROLLING AIRBORNE PARTICLES (Washington, Dc: National Academy
of Sciences, 1980); a short summary appears in FINE PARTICULATE
POLLUTION, a Report of the United Nations Economic Commission for
Europe (London and NY: Pergamon Press, 1979). A good, though very
technical, introduction is William Hinds, AEROSOL TECHNOLOGY;
PROPERTIES, BEHAVIOR AND MEASUREMENT OF AIRBORNE PARTICLES (NY:
John Wiley and Sons, 1982).
–Peter Montague, Ph.D.
Descriptor terms: particulates; air pollution; air quality;
incineration; epa policies; rcra; emmissions;