Animal tests (in vivo) have shown that carbon nanotubes (CNTs) can be found in different organs and cell types depending on their composition and method of administration (carbon nanotubes - uptake). Due to the manifold differences of applied nanomaterials, exposure pathways and analytical methods there emerges no clear picture on how carbon nanotubes behave once inside the body.

 

In view of possible adverse health effects as well as with regard to potential medical applications, studies of the distribution of carbon nanotubes inside the body (in vivo) is of great interest [1].

Different suspensions of carbon nanotubes.Different suspensions of carbon nanotubes.

Carbon nanotubes (CNTs) are usually delivered into the lungs of laboratory animals by inhalation, instillation or aspiration. No systemic toxicity of multi-walled carbon nanotubes (MWCNTs) could be observed in an inhalation study of several weeks with rats [2]. In case of installation and aspiration, the nanoparticles are first suspended in a liquid and then administered as droplets either directly into the lungs (instillation) or applied dropwise on the tongue followed by an inhalation step (aspiration).

However, the physiological relevance of both methods is questionable one the one hand because the nanoparticles aggregate within the liquid and on the other hand because the complete dosage is applied at once. A final judgement concerning the risks of exposure to carbon nanotubes under realistic workplace conditions is not possible now due to the limited amount of inhalation studies from independent laboratories.

 

Overview on different carbon nanotube structures: single-walled (SWCNT), double-walled (DWCNT), multi-walled (MWCNT) and possible surface modifications.Overview on different carbon nanotube structures: single-walled (SWCNT), double-walled (DWCNT), multi-walled (MWCNT) and possible surface modifications.

 

In different studies, carbon nanotubes were injected either in the abdominal cavity, the veins or into the lungs of laboratory animals [3-5]. In these cases, CNTs were mostly found in kidneys, spleen and liver or in the lungs. Once within the organs, they are frequently internalised by residential macrophages.

When carbon nanotubes were administered through the stomach, they were excreted within 12 hours without getting into the blood stream. Acute toxicity could NOT be detected in this study regardless of the application method [6]. However, up to now there are only few studies available regarding the influence of carbon nanotubes on internal organs [7].

 

Furthermore, carbon nanotubes are a very heterogeneous class of materials. Through various functionalisations, e.g. binding of a fluorescence dye for visualisation in microscopy, the surface properties of CNTs are altered which in turn also changes their behaviour in the body (distribution and retention time) [8]. It is possible to "control" the risk potential of carbon nanotubes by specific surface modification [7].

But due to the enormous variation of the material (purity, surface properties, applied dose and their agglomeration state, i.e. to which extent single carbon nanotubes stick together and form bigger particles) also the outcome of these studies is differing [4].

 

Due to the huge heterogeneity of carbon nanotubes and the differences in test designs and analytics, it remains unclear, how CNTs behave after their uptake into the body. The standardisation of test protocols in the future is absolutely necessary to solve this problem.

 

Literature arrow down

  1. Bianco, A et al. (2005), Curr Opin Chem Biol, 9(6): 674-679.
  2. Pauluhn, J (2010), Toxicol Sci, 113(1): 226-242.
  3. Singh, R et al. (2006), PNAS, 103(9): 3357-3362.
  4. Qu, GB et al. (2009), Carbon, 47(8): 2060-2069.
  5. Yang, ST et al. (2007), J Phys Chem C, 111(48): 17761-17764.
  6. Deng, X et al. (2007), Carbon, 45(7): 1419-1424.
  7. Johnston, HJ et al. (2010), Nanotoxicology, 4(2): 207-246.
  8. Wang, H et al. (2004), J Nanosci Nanotechnol, 4(8): 1019-1024.

 

 

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