ENGINEERINGnet.BE & NL IN THE FIELD Pathways in cell and tissue damage (part 1) The hidden hazards of nanomaterials Wat volgt is het eerste deel van een uitzonderlijke Engelstalige bijdrage van onze columnist Frank Moerman (KULeuven). Wetenschappelijke artikels over de veiligheidsrisico's verbonden aan nanomaterialen zijn eerder zeldzaam, en bovendien ontbreekt enig regelgevend kader. «Beter vroeg dan laat», een waarschuwing aan het adres van de preventie-adviseurs! O ndanks het feit dat de eerste wetenschappelijke onderzoeksresultaten aantonen dat veel nanomaterialen toxisch zijn voor levende organismen, worden ze toch met ongeziene snelheid in allerlei applicaties gebruikt. Nanomaterialen zijn een klasse materialen waarbij minstens één dimensie zich in de nanometer-range (10-9 m) bevindt. Koolstof nanobuisjes hebben dezelfde analoge structuur als asbest, en er zijn indicaties dat zij vele jaren na blootstelling (bv. inademen) dezelfde gezondheidsproblemen zullen veroorzaken, meer specifiek long- en buikvlieskanker. Zonder richtlijnen en wetgeving die beschrijven hoe deze materialen moeten behandeld worden tijdens productie, verwerking, toepassing en afvalverwerking, zullen verwerkers en gebruikers op korte of lange termijn mogelijks ernstige gezondheidsschade ondervinden. Er is dus dringend meer onderzoek vereist om per type nanomateriaal de schadelijke gezondheids- en milieu-effecten te bepalen, te meer omdat men niet zomaar de toxiciteit kan bepalen op basis van de eigenschappen die hetzelfde corresponderende materiaal in de millimeter-range bezit. Men moet de gezondheids- en milieurisico’s van nanomaterialen dus geval per geval onderzoeken. Frank Moerman, Catholic University of Leuven M any countries have developed programs to promote nanotechnology. Nanomaterials are all materials with a structural component smaller than 100 nm in at least one dimension. Besides nanoparticles that have three dimensions in the 1-100 nm range, there are also nanorods or nanotubes that have two dimensions in this range, and nanosheets or nanomembranes that have one dimension in this range. Nanoparticles of a specific material exhibit quite different physical (optical, electromagnetic), chemical (catalytic with increased chemical reactivity as result) and mechanical properties as compared to their larger counterparts, mainly due to surface and quantum effects. Because of these properties, nano-materials have the potential to alter physicochemical and biological characteristics. So, a material that is considered nontoxic in its larger-sized form might be extremely toxic at the nanoscale. Cntpolymermatrix. Engineered nanoparticles are materials engineered to create novel functionality or properties different from those of their larger counterparts of the same chemical composition. Safety concerns Safety concerns about nanomaterials are mainly driven by the accumulated knowledge of the health effects of inhaled anthropogenic nanoparticles, which are man-made in contrary to the nanoparticles commonly found in nature. Well-known natural nanoparticles are ash of volcanic eruptions, dust from desert storms, dust particles due to physical and chemical weathering of rocks, soot due to incomplete combustion during forest fires, extraterrestrial dust, etc. Anthropogenic nanoparticles (e.g., pollution due to vehicle and automobile exhaust, smoke and ash formed when burning wood, combustion of coal and petroleum for heating and power generation, waste incineration, occupational activities such as building demolition and welding, etc.) have shown to be maart 2015 maintenance MAGAZINE 21 ENGINEERINGNET.BE & NL IN THE FIELD Fig. 1 Lung lesions in rats after inhalation of nanomaterials: saline (A, F, K), carbon black (B, G, L), asbestos (C, H, M), multiwall carbon nanotubes (D, I, N), and grounded multiwall carbon nanotubes (E, J, O) (Buzea et al., 2007). Fig. 2 Diseases associated with nanoparticle exposure (Buzea et al., 2007) Fig. 3 At the cellular level, nanomaterials can interact with cells by various means. (1) Nanotubes can bind to receptors, (2) block the pores on the cell membrane and (3) damage the cell membrane. (4) Nanowire can puncture the entire cell responsible for the increase in cardiovascular, airway and pulmonary diseases, often resulting in death. The adverse health effects of pathogenic fibres, such as asbestos and silicates are well-known. Asbestos is responsible for lung and peritoneum mesothelioma (asbestos cancer), and because of their similar morphology, nanofibres and nanorods (e.g., single- and multiwalled carbon nanotubes) are suspected to exert the same damaging effects as asbestos after inhalation (Fig. 1). So, concerns have arisen that engineered nanoparticles, another category of man-made nanoparticles, might be toxic. Engineered nanoparticles are materials engineered at the nanoscale to create novel functionality or properties different from those of their larger counterparts of the same chemical composition. At present, the health effects of the long-term use of engineered nanomaterials and their interaction with other components such as proteins, lipids, carbohydrates and nucleic acids are not sufficiently known. Hence, before nanomaterials are largely 22 maintenance MAGAZINE maart 2015 membrane and (5) nanoparticles can physically rupture the cell membrane due to hyperthermic effects. Nanoparticles can be internalized into the cell (6) and the production of reactive oxygen species (ROS) (7) can be induced due to the high surface-to-volume ratio and the increased surface reactivity of these nanomaterials. High ROS concentrations are often associated with severe protein, DNA (8) and membrane (9) damage via excessive oxidation, resulting in induced programmed cell death in a vast number of cell types. The internalized nanomaterials can also damage subcellular organelles such as the mitochondria (10) and lysosomes (11), and stop their functions. All of these effects can disrupt cellular processes resulting in cell death (apoptosis and/or necrosis), chronic inflammation and fibrosis (Han et al., 2011). used in a wide range of applications, risk assessments must be performed to identify and quantify their potential toxicity. Notice that it is virtually impossible to extrapolate the adverse effects of nanoparticles from their bulk properties (Buzea et al., 2007; Pacheco-Blandino et al., 2012; Moerman, 2014). Nanomaterials in the body Nanomaterials can be absorbed by inhalation of free nanomaterials present in the air, by ingestion from food and water, and by penetration through the skin (Fig. 2). Once nanoparticles enter the body, they can penetrate the mucosal barriers of the gut and airways and travel through the circulatory systems, to finally deposit in various organs including the liver, kidneys and brain, where they can remain for weeks and months. Biostable nanomaterials (e.g., nanoparticles made of metal, such as quantum dots and silver; TiO2 nanoparticles; carbonbased nanomaterials such as fullerenes, carbon nanotubes, carbon soot; and silicon-based nanoparticles) have proven to exhibit long tissue retention times, in particular in the liver, spleen, and lymph nodes. Biopersistence, being the ability to penetrate into body tissues and to resist solubilization and normal clearance mechanisms (macrophage engulfment or renal/fecal excretion), is the main property of nanoparticles that may induce its longer term toxicity (Moerman, 2014). Adverse health effects of nanomaterials Some nanomaterials have been found to exhibit negative effects on tissues (Stone et al., 2009; Becker et al., 2011) (Fig. 3), as they may: • mobilize tissue macrophages eliciting sustained local inflammatory reactions, generally mediated by macrophage generated reactive oxygen species (ROS) and inflammatory cytokines; • cross membrane barriers, preventing entry of larger particles to the systemic circulation; • penetrate cell membranes, after which ENGINEERINGnet.BE & NL IN THE FIELD References they may initiate the formation of ROS that may cause oxidative damage to cells and impair cellular functional pathways. Oxidative stress at the cellular level may evoke acute and chronic inflammation, and also plays a significant role in the etiopathogenesis of several diseases, such as cardiovascular diseases, cancer as the consequence of uncontrolled cell proliferation, and neurodegenerative diseases as the consequence of premature cell death (apoptosis). Cytotoxicity of several nanomaterials Soto et al. (2005) performed comparative cytotoxicological assessment of several nanomaterials utilizing a murine lung macrophage cell line. Considering chrysotile asbestos as the positive control, and assigning it a relative cytotoxicity index of unity 1.0, relative cytotoxicities (relative cell viability (RCV) values) for the corresponding nanoparticulate materials Becker, H., Herzberg, F., Schulte, A. and Kolossa-Gehring, M. (2011), ‘The carcinogenic potential of nanomaterials, their release from products and options for regulating them’, International Journal of Hygiene and Environmental Health, 214 (3), 231-238. Buzea, C., Pacheco, I.I. & Robbie, K. (2007),’Nanomaterials and nanoparticles: sources and toxicity’, Biointerphases, 2, MR17-MR712. Han, Z.J., Levchenko, I., Kumar, S., Yajadda, M.M.A., Yick, S., Seo, D.H., Martin, P.J., Peel, S., Kuncic, Z. & Ostrikov, K. (2011), ‘Plasma nanofabrication and nanomaterials safety’, Journal of physics D: applied physics, 44 (17),174019-1 - 17409-8. 2014, 22-23 April, Ohrid, Macedonia, Journal of Hygienic Engineering & Design, 7, 8-29. Pacheco-Blandino, I., Vanner, R. & Buzea, C. (2012), ‘Toxicity of nanoparticles’, Ch. 14, in Pacheco-Torgal, F., Jalali, S. & Fucic, A. (eds.), Toxicity of Building Materials, Cambridge, United Kingdom, Woodhead Publishing, pp. 427-475. Soto, K.F., Carrasco, A., Powell, T.G., Garza, K.M. & Murr, L.E. (2005), ‘Comparative in vitro toxicity assessment of some manufactured nanoparticulate materials characterized by transmission electron microscopy’, Journal of Nanoparticle Research, 7 (2-3), 145-169. Moerman, F. (2014), ‘Antimicrobial materials, coatings and biomimetic surfaces with modified microtopography to control microbial fouling of product contact surfaces within food processing equipment: legislation, requirements, effectiveness and challenges’, Lecture at Central European Food Congress Stone, V., Hankin, S., Aitken, R., Aschberger, K., Baun, A., Christensen, F., Fernandes, T., Hansen, F., Hartmann, B., Hutchison, H., Johnston, H., Micheletti, C., Peters, S., Ross, B., Sokull-Kluettgen, B., Stark, D. & Tran, L. (2009), ‘Engineered Nanoparticles: Review of Health and Environmental Safety’, Final Report of the European 7th Framework Program ENRHES, Edinburgh Napier University, United Kingdom, 408 p. in the concentration range of 5-10 µg/ml were referenced to this substance (see table below). << In the next issue: «Toxicity of nanoparticles in current applications» Table: nanomaterials, morphologies and relative Cytotoxicity Index (Soto et al., 2005) Material Ag (silver; 99,99 %) (25 nm grade) Ag (silver; 99,99 %) A2O3 (-alumina) Component particle size Relative cytotoxicity* index (at 5 µg/ml) Relative cytotoxicity* index (at 10 µg/ml) 3-100 nm spherules; 30 nm (mean) 1.5 0.8 5-65 nm spherules; 30 nm (mean) 1.8 0.1 4-115 nm spherules; 50 nm (mean) 0.7 0.4 Fe2O3 (-iron oxide) 5-140 nm spherules; 50 nm (mean) 0.9 0.1 ZrO2 (zirconia) 7-120 nm spherules; 20 nm (mean) 0.7 0.6 TiO2 (80% anastase) 5-100 nm spherules; 40 nm (mean) 0.4 0.2 5-40 nm spherules; 20 nm (mean) 0.4 0.1 Irregular, short fibres 5-15 nm (diameter); 20-60 nm (length) 0.3 0.05 10-150 nm spherules; 60 nm (mean) 0.4 0.06 15-40 nm fibre diameter; 20 nm (mean) 0.5 - 15 µm length ; ~ 5.:1 – 500:1 aspect ratio 1.0 1.0 2-50 nm spherules; 20 nm (mean) 0.8 0.6 Nanoropes/bundles 10-200 nm diameter 1.1 0.9 Multi wall carbon nanotube powder (MWCNT) ~ 50 % nanotubes; 10-30 nm (diameter) 50 nm - 1 µm fibre (length) ~ 50 nm fullerene diameters 1.1 0.8 Multi wall carbon nanotube powder (MWCNT) ~ 85 % nanotubes; 3-5 nm (diameter) 15 nm (mean); 20 nm - 1 µm lengths 0.9 0.8 TiO2 (anastase) TiO2 (rutile) Si3N4 (silicon nitride) Chrysotile Asbestos Mg3Si2O5(OH)4 Carbon black powder Single wall carbon nanotube powder (SWCNT) * Referenced to asbestos, an index less than 1 represents lower toxicities, while higher values reveal higher cytotoxicity maart 2015 maintenance MAGAZINE 23
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