Animal Studies Demonstrate Problems
 
The only two clinical safety studies I’m aware of dealing with the inhalation of silver into the lungs were conducted on laboratory rats. 
 
Both studies used laboratory engineered silver nanoparticles, rather than commercial colloidal silver.  But the idea of what happens to silver when it’s inhaled daily into the lungs for long periods of time is what was looked at.
 
The first study was a 28 day study which concluded there was no significant long-term harm to laboratory rats that were forced to inhale various levels of silver nanoparticles for varying periods of time on a daily basis for four weeks.  That’s definitely good news.  Very exciting!
 
The second study, however, was conducted on rats over a period of 13 weeks (i.e., 90 days). It concluded that there were “dose-dependent increases in lesions related to silver nanoparticle exposure, including mixed inflammatory cell infiltrate, chronic alveolar inflammation, and small granulomatous lesions. Target organs for silver nanoparticles were considered to be the lungs and liver in the male and female rats. No observable adverse effect level of 100 μg/m3 is suggested from the experiments.”
 
In other words, at higher daily doses for longer periods of time there were significant negative results including chronic inflammation of the alveolar, i.e., the delicate air sacs deep within the lungs where oxygen is taken into the bloodstream. 
 
Also observed by the researchers were increases in inflamed cells, and small nodules, or tiny lumps of inflamed tissue. And silver nanoparticles apparently accumulated in the lungs and liver of the rats.
 
Interestingly, in this study there were no observable adverse effects at 100 ug/m3, or 100 micrograms of silver per cubic meter of air.  Once again, that’s at least somewhatencouraging news because it indicates that when silver is inhaled daily, there apparently are levels of silver inhalation which -- at least in the rat model -- are relatively safe even when used for weeks on end.  But beyond those levels significant negative results were indeed observed.
 
The study researchers wrote: 
 
The results…indicated that lungs and liver were the major target tissues for prolonged silver nanoparticle accumulation.
 
…Based on the test article–related effects (minimal bile-duct hyperplasia in males and females, chronic alveolar inflammation and macrophage accumulation in the lungs of males and females, and erythrocyte aggregation in females) reported in this study, we found a NOAEL of 100 ug/m3.
 
…lung function changes previously reported from this study (Sung et al., 2008) indicate significant physiological decreases in tidal volume for all dose levels in males and minute volume decreases for all dose levels in females. The origin of the difference in effects measurements remains to be resolved.
 
This basically means that over the course of 90 days of inhaling the silver nanoparticles each day, the tiny silver particles accumulated in the lungs and livers of the rats.
 
What’s more, the tiny air sacs in the lungs known as the alveoli became inflamed, and as a result lung function was significantly reduced.  The reduction in lung function was higher for male rats than it was for female rats in the study.  The researchers don’t know why.
 
Finally, macrophage accumulation in the lungs of these rats would seem to indicate the body was attempting to remove foreign substances from the lungs, i.e., the accumulated silver. 
 
A macrophage is a form of phagocyte. And a phagocyte is a cell, such as a white blood cell, that engulfs and attempts to eliminate toxic substances, waste material, harmful microorganisms, or other foreign materials in bodily tissues as well as in the bloodstream.
 
Remember, these rats were not sick.  They were simply inhaling silver nanoparticles.  So there would have been no reason for the body to send macrophages into the lungs except to remove accumulated silver particles from the lung tissues.
 
This is similar to what’s observed when people are exposed to inhalation of asbestos on a chronic basis.  The asbestos lodges in the lungs.  And the body sends in macrophages whose job is to attempt to rid the area of the accumulated foreign objects by engulfing them. 
 
In short, macrophages are the “clean-up crew” of the human body, and they’re only called in when there’s something to clean up.
 
This demonstrates pretty much beyond any shadow of a doubt that silver particles, when inhaled regularly, over long periods of time, can become embedded in the soft tissues of the lungs and cause a decrease in lung function.