Silver nanoparticles can be absorbed by the body and after overcoming the body barriers – either as nanoparticles or ions – can be transported through the body and accumulate in the organs.

 

Possible entry routes of silver nanoparticles into the human body. © Eckhardt et al. (2013), Chem Rev, 113(7): 4708-4754.Possible entry routes of silver nanoparticles into the human body. © Eckhardt et al. (2013), Chem Rev, 113(7): 4708-4754.

The most important entry pathways for silver nanoparticles into the body are via the lungs or via the gastrointestinal tract (see section "Uptake"). Silver nanoparticles have shown to mainly accumulate in different organs such as the liver and kidney but also in spleen, testis and brain. In some cases, gender-related differences in the distribution and retention time of the silver nanoparticles in different organs has been be observed. Female test animals had an increased incorporation of silver in the kidneys whereas the male counterparts displayed a persistent accumulation of silver in the brain and testes. The reasons behind these observations are yet unknown. In general, the distribution pattern of the silver nanoparticles inside the body depends on various factors such as dose, particle size and duration of exposure which also affects the potential toxic effects.[2,4,10,12-14]

So far the immune system has only been shown to be impacted by silver nanoparticles when using extremely high concentrations, far beyond any realistic exposure. Furthermore there is no concrete evidence that nano silver can cause allergies.[1,3,9,10,13,15]

Regardless of the different exposure routes, silver nanoparticles can undergo various biochemical transformations once inside the body for which a variations in particle coating plays an important role. For example, in the stomach the silver nanoparticles dissolve faster due to the acidic environment resulting in an increased release of silver ions. Since silver ions are very reactive they usually agglomerate immediately upon release or interact with and bind to other chemical compounds meaning they no longer exist as ions or nanoparticles. To that effect the silver-ion-complexes (also called organo-silver-complexes) rather than the original silver nanoparticles are taken up and distributed throughout the body. Altering the surface of the silver nanoparticles by means of different coatings allows for a selective adjustment of the ion-release behaviour of the silver nanoparticles.[5,7,11]

 

Up to now there is no evidence that the body is able to metabolise silver ions. With the help of the various detoxification mechanisms within humans, the silver ions are primarily inactivated by binding to other chemical compounds or proteins and then incorporated into the tissues as non-toxic silver complexes (e.g. as silver sulphide). Excretion of silver nanoparticles usually occurs via faeces and urine but very few data are available for this.[5,6,8]

 

Literature arrow down

  1. Chuang, HC et al. (2013). Int J Nanomedicine, 8 4495-4506.
  2. Ji, JH et al. (2007). Inhal Toxicol, 19(10): 857-871.
  3. Kim, JS et al. (2013). Nanotoxicology, 7(5): 953-960.
  4. Kim, YS et al. (2008). Inhal Toxicol, 20(6): 575-583.
  5. Liu, J et al. (2012). ACS Nano, 6(11): 9887-9899.
  6. Loeschner, K et al. (2011). Part Fibre Toxicol, 8 18.
  7. Mwilu, SK et al. (2013). Sci Total Environ, 447 90-98.
  8. Park, MV et al. (2011). Biomaterials, 32(36): 9810-9817.
  9. Stebounova, LV et al. (2011). Part Fibre Toxicol, 8(1): 5.
  10. Van Der Zande, M et al. (2012). ACS Nano, 6(8): 7427-7442.
  11. Wang, X et al. (2014). Small, 10(2): 385-398.
  12. Xue, Y et al. (2012). J Appl Toxicol, 32(11): 890-899.
  13. Hadrup, N et al. (2014). Regul Toxicol Pharmacol, 68(1): 1-7.
  14. Foldbjerg, R et al. (2013). Archives of Basic and Applied Medicine, 1(1): 5-15.
  15. SCENIHR (2014). Report: "Opinion on Nanosilver: safety, health and environmental effects and role in antimicrobial resistance.", ISBN: 831-4783.

 

 

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