Engineered versus incidental nanoparticles in the atmosphere


About the author: Dr. Linsey Marr is a professor in the Department of Civil and Environmental Engineering at Virginia and part of of VTSuN.

Take a deep breath. You just inhaled about 1 million particles. Figure 1 shows various types of airborne particles, also known as aerosols, under a microscope.

Figure 1. Electron microscope images of (left to right) volcanic ash, pollen, sea salt, and soot from largest (several thousand nanometers across) to smallest (tens of nanometers per individual “grape” in the bunch of soot). Image from http://earthobservatory.nasa.gov/Features/Aerosols
Figure 1. Electron microscope images of (left to right) volcanic ash, pollen, sea salt, and soot from largest (several thousand nanometers across) to smallest (tens of nanometers per individual “grape” in the bunch of soot). Image from http://earthobservatory.nasa.gov/Features/Aerosols

Most of the particles in the atmosphere are smaller than 100 nanometers, or about 1000 times smaller than the width of a human hair. Scientists call such particles, “nanoparticles.” Airborne nanoparticles are not new. Ever since there have been fires and windblown dust, very small particles have been suspended in the atmosphere. So what is the difference between “engineered” nanoparticles and “incidental” nanoparticles? And if there is a difference, does it matter?

Have you ever tried to make breadcrumbs from a slice of bread? Maybe you toasted the bread or let it get stale and then tried to smash it with a rolling pin or some other tool? Or maybe you were making graham cracker crumbs for a cheesecake? These are intentionally “engineered” crumbs. You also know that if you eat a piece of toast or a graham cracker, you inevitably leave behind some crumbs. These are “incidental” crumbs. Likewise, engineered nanoparticles are intentionally manufactured in order to serve as an ingredient in some product, whereas incidental nanoparticles are unintentionally produced as a byproduct of some other activity. For example, driving a gasoline-powered car produces incidental nanoparticles from combustion of the fuel.

Presently, many engineered nanoparticles are made of certain types of metals and other materials that are not found as commonly in incidental nanoparticles. Engineered and incidental nanoparticles may also differ in shape. Titanium dioxide is a naturally occurring mineral that is processed to make titanium dioxide nanoparticles for use in sunscreen, paint, and other products. However, titanium dioxide is not abundant in the atmosphere. On the other hand, soot nanoparticles, which consist mainly of carbon, are commonly found in the atmosphere as incidental nanoparticles. Carbon appears in engineered nanomaterials such as fullerenes, carbon nanotubes, and graphene, shown in Figure 2, in which it has a more regular shape and structure than in soot.

Figure 2. Fullerene, carbon nanotube, and graphene. Images from http://web.ornl.gov/~pk7/pictures/c60.html, http://blog.epa.gov/science/2012/12/for-the-win-benzene-challenge-yields-a-solution/, and http://www2.lbl.gov/Science-Articles/Archive/sabl/2007/Nov/gap.html
Figure 2. Fullerene, carbon nanotube, and graphene. Images from http://web.ornl.gov/~pk7/pictures/c60.html, http://blog.epa.gov/science/2012/12/for-the-win-benzene-challenge-yields-a-solution/, and http://www2.lbl.gov/Science-Articles/Archive/sabl/2007/Nov/gap.html

Many studies have shown that inhalation of incidental nanoparticles is associated with premature mortality, heart disease, lung cancer, asthma, and other health effects, but scientists still do not know exactly what it is about the particles is harmful. If it is merely the presence of some small, foreign objects in the lungs, then the difference between engineered nanoparticles and incidental ones may not matter, but if the chemical composition or shape matters, then the difference could be important. In everyday life, we don’t need to worry about breathing nanoparticles in the air if it is relatively clean, as in most areas in the US, but we should be careful about being too close to exhaust or exercising vigorously on a polluted day.

One thought on “Engineered versus incidental nanoparticles in the atmosphere

  1. The Beauty and Mystery of the Microworld
    The beauty of these pictures is intriguing and fascinating by its asymmetric, exquisite and intricate pattern. What is it? Is it a product of a novel computer program or photographs of fine creations of nature? Neither statement is true. In fact these are not pictures, but images of metal samples made with an electron microscope. Only some color is added to the images to emphasize their resemblance to natural objects of our macroworld: seashells, jelly-fish, leaves of exotic plants. The size of the samples is from tens of micrometers to 1-2 millimeters. They are produced by self-arrangement of nano-sized (million fractions of a millimeter) wires growing on porous membranes under the action of electric current pulses. This is how such bulk (3D) sculptures are described in scientific journals [1, 2, 3] along with the experimental conditions for their reproduction, i.e., the conditions of the process (electrolyte composition, porous membrane, pulsed current mode) are specified and growing nanowires arrange themselves in an inexplicable fashion into “sculptures” that show perfect resemblance to natural creations. The authors have managed to isolate and examine them and then produce them “by order”. Besides, they have proved that the internal structure of these metallic “shells” is a bulk multilayer network woven by nano-sized wires photographed with a modern electron microscope. Such antenna-like samples are expected to find application in nanotechnolgy. Now we can produce such “sculptures” from various metals and admire their elegant forms and fascinating beauty. However, it is still a riddle. Why do they so closely resemble shells and leaves? Does this mysterious self-arrangement have anything in common with formation of plant leaves and seashells?
    [1] J of Bionic Engineering 10 (2013) 368–376 [2] Materials Today 16 (2013) 98–99 [3] Materials Letters, May (2014).

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