This paper narrates the information about nanotoxicology. Nanotoxicology is a study of nano materials. There is information regarding current usage forms of nano particle in different technologies in different field. Nano materials are very special in the form of their properties. They are very fast reacting, having high surface area and they have higher than usual penetration power. However, these properties are also going against living beings affecting human and other animals' health. Particles gets entered into body either by accidently or by intentionally. In the body ultimately most of the nano material affects DNA functionality and lead to abnormal protein production. There is mentioning of two studies in this paper. One is regarding Ti02 effect upon p53 gene. This proves that Ti02 has adverse effects deviation p53 functionality. The other study is of Carbon Nano tubes [CNT]. This study also emphasizes upon inhalational adverse effect of CNT in rats. There are some suggestions for modification of current methods in research also.
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Toxicology is a study of toxicity of particles sized between 0 to100 nanometer. Study of toxicity caused by nanoparticles is mandatory to determine whether nanomaterial is detrimental to environment and so to human beings. Nanoparticles generally are used in medicines, electronics and biomaterials.
Commonly used nanoparticles in routine life are of following classes:
Fullerenes: Bucky balls and Carbon tubes. Both are porous molecules and having lattice-like structure [S. Sapmaz, P. Jarillo-Herrero, L.P. Kouwenhoven, and H.S.J. van der Zant, 2006]. Liquid crystals: They are used in pharmaceuticals to deliver various types of drugs safely. They mimic natural biomolecules like protein and lipid. Liposomes: They are types of liquid crystals but they are lipid based. They are also used in pharmaceutical and cosmetic industries. Nano shells: They are spherical cores of nanoparticle surrounded by a shell which is sized in nanometers. One common formula for creating Nano shell is to use silica as core and gold for making shell surrounding the core of silica. This formula commonly used in making remedies for treatments of cancer. Quantum Dots: Quantum dots are actually semiconductors emitting light in different colors [Tae-Ho Kim, Kyung-Sang Cho, Eun Kyung Lee, Sang Jin Lee, 2011]. They are basically used in labeling and imaging the cancer cells. Super paramagnetic nanoparticles: They are nanoparticles which retain magnetism even after magnetic field is removed. Iron oxide with <100 nm is used in selective bio separation. They are very useful in MRI technics, drug delivery and membrane transport study. Dendrimers: They are branched nanoparticles and they are mainly used in identification tags like enzymes and florescent dyes. Nano rods: They are Nano cylinder of silicon. They are used in Nano medicine for imaging and contrast studies.
Various products using Nano particles:
Cosmetics, Automobiles, refrigerators, Cell phones, Clothes, etc. Ti02 has been widely used in various industries like plastics, food industries, colors industries and it is now accepted as biologically inert particle [Chen et al., 2005; Bernard et al., 1990; Hart et al., 1998]. Ti02 is also widely used in pharmaceutical industries [Lee et al., 1985; Bingham et al., 2002; Lomer et al., 2002; Gelis et al., 2003].
Properties of nanoparticles:
Higher surface area, higher permeation and higher reactivity giving advantage over macro particles in every aspects of reaction [Colvin et al., 2003; Oberdorster et al., 2004]. All these properties of Nano particles are also responsible for harmful effects, making them potentially harmful substances. Nano particles can easily break through epithelial surface [Clurg et al., 1998]. These particles also enter into the blood via inhalational route [Donaldson et al., 2001; Nemmar et al., 2001], then they can easily involve other body organs [Samet et al., 2004]. Technologies which are using nano technology are also potentially danger to health.
Common routes of exposure:
People working in nano technology industry and those who are using product based on nano technology are more susceptible to exposure and get affected by nano particles. Some routes like oral ingestion, inhalation and skin contact are rapidly acting and routes like soil and water dissolution are slower exposure routes, through these routes nano particles get accumulated gradually in the body tissues and then after a long time they show toxicity. It is unlikely that nano particle penetrate the skin as even though they are nano in size they are still larger for passive transport. Sign and symptoms are ranging from mild to severe depending upon dose and type of particle and its toxicity. Toxicity of every particles are different and so some particle require small amount of dose while some less toxic particles require more dosage and causes deviation of health markedly only after a long time of exposure. Due to lack of specific regulation over usage of nanotechnology, knowingly and unknowingly its usage is getting increased despite of many adverse effects. Many studies are under going to figure out various effects of different nano particles over health.
Mechanisms of toxicity:
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After entering into body tissues particles integrate into normal mechanisms of cell and generate reactive oxygen molecules, which are also known as superoxide radicals. Some examples are hydrogen peroxide, superoxide anion. These radicals are having an electron in their outer orbit which is helping radicals in interaction with different tissues like protein and lipids. Besides these nano particles causes breakdown of proteins and lipids leading to imbalance of cellular homeostatic mechanism. Particles also known to cause direct DNA damage, Ultimately either leading to cell apoptosis or abnormal protein production and abnormal cellular function.
Some studies also shows that particles like Ti02 induces oxidative stress in cells [Ramires et al., 2001; Zhang et al., 2004; Gurr et al.,2005; Hussain et al., 2005].
[Dunford et al., 1997; Rahman et al., 2002; Gurr et al., 2005; Wang et al.,2007]
Current research questions worth consideration:
[Toxicological Sciences (2004) , Vol. 77, pp 4-5]
Methods for study of toxicity of nano particles:
To start the study one has to know duration and route of exposure, dosage of material, reference material for comparison, biological species for testing and the question what to measure.
[Nature nanotechnology (2009), Vol. 4, page 395]
(i) One example of study of toxicity of nano particles is study of Ti02 triggers P53 response in peripheral lymphocytes. This study was performed in vitro by Su Jin Kang and his team mates of School of Public Health and Institute of Health and Environment (Seoul National University, Seoul, Korea). In study they collected of lymphocytes from a healthy adult female donor after her consent. Then lymphocytes were exposed to sterilized nano-Ti02 in vitro then they measured cell death and underlying mechanism leading to toxicity in peripheral lymphocytes using various tests like Micronucleus essay, Single-Cell Gel Electrophoresis Assay, Western-Blot Assay.
[Su Jin Kang, Byeong Mo Kim, Young Joon Lee and HaiWon Chung, 2008]
Above image shows response of cytotoxicity related protein to nano-Ti02. It shows that the level of p53 and p63 were up regulated by nano-Ti02 and phosphorylation of p53. Conclusion of the study: After examination of toxic effects of nano-Ti02 they have concluded that lymphocytes treated with nano-Ti02 shows increase in micronucleus formation and DNA damage. Western-Blot analysis revealed the accumulation of p53 and activation of DNA damage checkpoint kinases. However Ti02 doesn't stimulate transactivation activity of p53. They also observed formation of superoxide oxygen radicals. After N-Acetylcysteine supplementation the nano-Ti02 induced DNA damage was inhibited. Thus, nano-Ti02 particles induce formation of superoxide anions which activates p53 and p53 causes DNA damage [Environ. Mol. Mutagen. 49:399-405, 2008]. (ii) Another example of study regarding toxicity of nano particles is type of in vivo. This study was performed upon rats. The study led by Robert Landsiedel, Germany under the heading "Inhalation Toxicity of Multi-wall Carbon Nanotubes in Rats Exposed for Three Months" and was published in Toxicological Sciences. Unlike other studied of this kind, where the carbon nano tubes (CNT) were instilled directly into the lungs of the mice, method used in this study was pharyngeal aspiration. The reason behind for choosing this method of instillation is that the method of direct instillation of CNT into lungs is under debate as it may overestimate the effect of particle over natural inhalational pathway though trachea and may influence the risk assessment results. Methodology: The CNT aerosol particles (diameter 5-15 nm, length 0.1-10 Î¼m) were generated successfully by a brush generator (Ma-Hock et al., 2007) without damage to structures of the tubes. Then male and non-pregnant female rats were divided randomly to four test groups and then they were exposed to CNT aerosols for ninety days with concentration of 0 (for control), 0.1, 0.5 or 2.5mg/m3 with a constantly maintained pressure. The concentration of aerosols was monitored continuously throughout exposure. Results: There was no development of signs and symptoms during 90 days of study and there were no premature death. However, with concentration at 0.5 and 2.5mg/m3, the samples from lung revealed grey discoloration and concentration dependent lesions in the lungs and lymph nodes which are signs of inflammation and granuloma formation. The lowest concentration at which adverse effect detected was 0.1mg/m3. Conclusions of this study: Although there were uncertainty about generation of aerosol in nm size range , the results of the study indicates the inherent toxicity even at very low level of carbon nano tubes [Teeguarden, Robertson, Waters, Murray, & Jacobs, 2011]. These results may be due to similarities between asbestos and carbon nano tubes. Besides this study an another study led to conclusion that CNT has effect against E.Coli and reduces its virulence [Langmuir (2007), Vol. 23, page 8671].
Conclusions and Recommendations
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Although, there is not sufficient data regarding mortality and morbidity due to nano particle toxicity, we cannot deny its adverse effects upon living beings like us. Those studies which are mentioned in this paper have shown some evidence about ill effects of nano particles and bagging some serious research in to this matter. Each day a new nanotechnology arrives with new nano particles, which are not yet know may have new kind of effects and may be serious after a long time.
Need for change in methods:
Methods for determination of toxicity should be changed according to nanotechnology development and other needs. In vitro test are more cost and time effective and there are no ethical issues. Also improving in vitro techniques would increase accuracy of test and so results [Nature nanotechnology (2009), Vol. 4, page 342].
For example, while measuring quantum dot toxicity in liver cell with 3D techniques, it was lower than 2D techniques [Small 2009, 5, page 1213-1221].