Size Matters
Dr. Hildegarde Staninger

TABLE 1: Size of Various Viruses and Microorganisms as Compared to the Diameter of a Human Hair.
Note: 10 nanometers (nm) is 1,000 times smaller than the diameter of the human hair. There are as many nanometers in an inch as there are inches in 400 miles.
 Category  Nucleic
 Papova-virus  DNA  45  Polyoma Mouse 
 Adeno-virus  DNA  80  Types 3, 7, 12, 18 & 31  Human
 Retro-viruses  RNA   70 to 110  Rous sarcoma Chicken 
 Herpes-virus  DNA  100  Epstein-Barr  Human
 Orthomyxoviridae  RNA   80-120  Influenza A Humans, Birds 
        Influenza B    Humans, Seals
       Influenza C  Humans, Pigs
Special Note: The Orthomyxovirdiae are a family of RNA viruses which, so far as is known, infect mainly vertebrates (Thogotovirus in ticks, Isavirus in the sea louse). It includes those viruses which cause influenza.
Influenza A virus particle or virion is 80-120 nm in diameter and usually rightly spherical although filamentous forms can occur.
A virion has been made by man and is a virus that has been broken up into 150 pieces.
Origin of Viruses
Viruses are the living dead and they are not cells. There are three possibilities on the origin of viruses:
*        If they are not cells and require living cells for replication, then viruses must not have been present prior to cellular evolution and could therefore have coevolved with cells.
*        Were once cells but have lost all cellular functions retaining only infomraiton to replicate themselves using hosts machinery.
*        Viruses have evolved from plasmids (plasmids are self replicating independent DNA) or from RNA viroids. These "early" viruses did not contain genes for capsids. As viroids moved from cell to another, it picked up such genes.
There are some 4000 viruses belonging to 71 families, 11 subfamilies, and 175 genera are known in 1995.
General Characteristics
*        Viruses (poisons) are obligate microorganisms, filterable and infectious particles. For example plant sap with a virus in it can infect other hosts.
*        20 nm to 14,000 nm in size.
a. Most are smaller than bacteria (eg. Adeno-virus)
b. Vaccinia virus is the same size as the small bacteria like Mycoplasma Rickettsia and Chlamydia.
*        Contain either DNA or RNA (never both) surrounded by a protein coat (capsid) and sometimes covered by an envelope.
*       Obligate intracellular entity and multiply inside living cells by using cellular Synthesis machinery
TABLE 2: Comparative Sizes of Biological Objects Diameter
 Limit of
Human eye (100 um)
 Ostrich egg  200,000
human ovum
Light microscope
(0.2 um) 
(red blood cell)
Serratia marcescens
Rickettsia species
   Clamydia psittaci 0.27 
Electron microscope 
(0.001 um*)
 Mycoplasma species   0.15
  Influenza virus   0.085
  Genetic unit
(Muller's Est. of largest
size of gene)
0.02 x 0.1251   20 x 1254
  Poliomyelitis virus   0.027   27
   Tobacco necrosis  plant 0.016 16 Virus 
  Egg albumin molecule 
(protein molecule)
0.0025 X 0.01+   2.5 x 10+
   Hydrogen molecule 0.0001   0.1

*For most biologic specimens the limit of resolution of the electron microscope is 0.001 um, or 1 nm.  Under special conditions, resolution may be obtained at 2 or 3 Angstroms. +Width x Length
Taken from: Smith, Alice L.  Principles of Microbiology, 10)th (ed). Times Mirror/
Mosby College Publishers. St. Louis, Missouri. © 1995 pg. 145
TABLE 3: Equivalents in the Metric System
Nanometer8   0.1 NM
Meter (m) 1 100 1000
1,000,000,000  1010 
  0.01  1 10
1 1000 
10-3 1
 1000   10,000
Millimicron (mu)
10-3  101 
   Hydrogen molecule 0.0001   0.1    
Taken from: Smith, Alice L.  Principles of Microbiology, 10th (ed). Times Mirror/Mosby College Publishing. St. Louis, Missouri. © 1995 pg. 144   
Classification, Definitions, Properties, Hazards, Risks and Toxicology of Nanoparticles and Nanotechnology
The Surprising Toxicology Of Nanoparticles
Size Matters
Size may have another crucial biological consequence: where nanoparticles end up in the body.
A complex of physical factors such as aerodynamics, gravity, and mass causes the largest inhalable dust particles to deposit primarily in the nose and throat. Any toxic effects occur at that site (for example, nasal cancers due to wood dust). Smaller particles are deposited in upper airways and are expelled by the "mucosociliary escalator;" the fingerlike cilia and the mucous lining of the trachea and bronchial tubes, which together move particles up into the throat and nose, where they are coughed, sneezed, blown out, or swallowed. Any toxic effects usually result from absorption through the gut (lead poisoning for example).
The next smallest particles penetrate deeper into the alveolar region (where oxygen and carbon dioxide are exchanged in and out of the blood) and are usually cleared when alveolar macrophages (special monocytic scavenger cells in the lungs) engulf the particles and carry them away. But if a high concentration of NSPs is inhaled, the sheer number of particles - especially if they do not agglomerate - can overwhelm those clearance mechanisms, and they can penetrate to different parts of the respiratory tract. Toxic effects are usually due to killing of the macrophages, which causes chronic inflammation that damages lung tissue (asbestosis and silicosis are examples).
At sizes less than 100 nanometers, inhaled particles begin to behave more like gas molecules and can be deposited anywhere in the respiratory tract by diffusion. Like gases, NSPs-whether natural, incidental, or engineered-simply because of their "nanoscopic" size, can pass through the lungs into the bloodstream and to be taken up by cells, within hours reaching potentially sensitive sites such as bone marrow, liver, kidneys, spleen, and heart.
As particles become small compared to the size of a cell, they can begin to interact with the molecular machinery of the cell. The central nervous system's olfactory bulb (where aromatic molecules are detected) seems to be able to absorb NSPs smaller than 10 nm from the nasal cavity - which then can travel along axons and dendrites to cross the blood-brain barrier.
Inhalation is not the only route into the body. When ingested, NSPs can end up in the liver, the spleen, and the kidneys. When touched, NSPs in the range of 50 nm and smaller tend to penetrate the skin more easily than larger particles (although other aspects such as charge and surface coatings of the particles are also important), sometimes, being taken up by the lymphatic system and localizing in the lymph nodes. (See Figure 3, below.)
By the same token, the mucosociliary escalator is also not the only way out of the body. There is evidence suggesting that nanoparticles could be excreted through urine. However, excretion routes for nanoparticles (urine, feces, sweat) are likely to vary depending on exposure route, size, charge, surface coating, chemical composition, and many other factors.
For incidental exposure, all this uptake of NSPs into internal organs could be of concern. But for therapeutic exposure, it is exciting, as it suggests that engineered nanomaterials can be used to target therapies to specific organs, even ones normally quite difficult to reach (such as the brain).
So far, results from different investigators are more suggestive than definitive. More research needs to be done on methods of administration, means of uptake, and on the body's clearance mechanisms. Also, when nanometer-sized particles are generated in combustion processes, most collide with other particles, are held together by the strong surface tension, and agglomerate into larger particles. The distribution of particles sizes will depend on the density of nanometer particles at the point of generation. One of the early priorities for nanotechnology health research is to gain a better understanding of the particle sizes that are likely to be associated with the production of engineered nanoparticles.
Still, size is not the only thing that matters for potential toxicity,%2
Nanoscale particles can end up in different parts of the body depending on size and other characteristics as well as routes of entry. Although many uptake and translocation routes have been demonstrated, others still are hypothetical and need to be investigated. Translocation rates are largely unknown, as are accumulation and retention in critical target sites and their underlying mechanisms. These, as well as potential adverse effects, largely depend on physicochemical characteristics of the surface and core of NSPs. Both qualitative and quantitative changes in NSP biokinetics in a diseased or compromised organism also need to be considered.
Shape Matters
Although the shapes of NSPs also give them unique properties, under the Toxic Substances Control Act (TCSA) engineered nanoparticles may not be viewed as new compounds unless they have a unique composition. For example, TiO2 nanoparticles are handled the same way with respect to regulation as bulk TiO2, even though the two forms have different properties.
Some studies show that the materials having the same composition but of different shapes as well as sizes have different toxicities - moreover, not with a linear relationship as one might expect. For example, one study showed that nanoparticles 50 to 130 nm across of quartz-crystalline silica (a substance known to be toxic) were less toxic than 1.6-mm particles - but that 10-nm particles were actually more toxic. But route of entry into the body as well as dose also affect toxicity.
Purity Matters
Bulk carbon in macroscopic components is medically useful because it is not poisonous to or rejected by the body. Yet, some researchers have observed from experiments that carbon nanotubes (especially single-walled or multi-walled carbon nanotubes) seem to be more toxic than other forms of carbon. Others have debated that claim because the nanotubes used had trace impurities of iron or solvents. Indeed, some studies suggest that other forms of nanoscale carbon such as C60 fullerenes might prevent toxicity by being antioxidants.
Possibly at stake here, or in similar debates over other engineered nanomaterials, may be the purity of the engineered nanomaterials. At this stage, people don't have absolutely repeatable control on manufacturing processes; nanotech production is now roughly where the production of indium gallium arsenide phosphide (InGaAsP) semiconductor lasers were in the early to mid 1980s - relatively low yield of reliable production. Thus, buckyball products from one supplier are not necessarily identical to those from another, so toxicity may differ. Ask sources careful questions about the size of particles, their manufacture, experimental methods, whether they characterized the materials themselves at the time when they performed the experiment or simply believed the statements made by the supplier, and the comparison of their results with other studies.
Stay Tuned
With more research under way, there are more and new publications reporting on nanotoxicology. Until more is certain, the National Institute for Occupational Safety and Health (NIOSH) has announced research needs and interim guidelines for protecting workers in nanotech industries in its report Approaches to Safe Nanotechnology.
Primary author: Trudy E. Bell
Source: National Nanotechnology Initiative (NNI)
For more information on this source please visit National Nanotechnology Initiative (NNI)





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