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Human Exposure of Nanoparticles and Health Hazard Risks

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In the past, nano-sized particles are produced accidentally from the forest fires and volcanoes by-products, and various processes carried out in industry at high-temperature including combustion, grinding, welding and vehicle combustion. Nowadays, the wide use of Nanomaterials in medicine (e.g., molecular targeted therapies, diagnostic imaging), consumer goods (e.g., cosmetics, baby products, electronics), and building materials (e.g., concrete, windows, steel). These materials are act according to their physicochemical nature. For example, nanomaterials such as carbon nanotubes (produced artificial implants) used to add mechanical strengt and SiO2 nanoparticles (food packaging) are often used to add durability TiO2 nanoparticles are used to increase the degree of hydration (as water purification), and FeO3nanoparticles are used for abrasion resistance. Study of the negative health impacts of exposure to very small particles in air pollution, coal and silica dust, welding fumes and asbestos is informing the emerging field of nanotoxicology, but much more research is needed to understand the health risks of nanomaterials already used in hundreds of products world-wide.

The Royal Society/Royal Academy of Engineering report identified multiple scenarios through which humans could become exposed to engineered nanomaterials including occupational, environmental and consumer exposure. In occupational exposure of NP’s occurred at various phases of the material life cycle along with nature of exposure, level of exposure and number of people involved there. During the development of new products, the processes are occurred in laboratory conditions. So, at that condition there was a very small quantity of products were produced which gives lesser exposure but may be exposed accidently. Later, in commercial production the chances of exposure increased during the product synthesis because of the increase the size of the product and may also during downstream activities such as recovery, packaging, transport and storage. The exposure may also due to the lack of regulations and standards in the product manufacturing.

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The new products containing nanomaterials are used by individuals in routine days. The “new and improved” products are used due to their purported benefits. Examples include waterproof pants, socks that eliminate foot odor, stain-resistant shirts, pacifiers that fight bacteria etc. However, the long-term exposures to some products are not certain to the potential human health risks, but there is a lack of exposure data to evaluate if these products are safely performing their intended purpose. Our understanding of materials science, coupled with our ability to rapidly implement nanomaterials into engineered products, may have outpaced our analytical ability to accurately quantify human exposure. Currently, there are no universally accepted measurement procedures — analytical methods — established for measuring human exposure to nanomaterials precisely. This may be ascribed to the unique physicochemical properties of nanomaterials as compared to bulk materials, such as soil or dust, or volatile chemicals, such as benzene, PAHs, and TCE. The currently employed analytical methods are dynamic, mostly involving a modification of conventional methods for quantifying micro-sized materials.

The toxicity of nanomaterials are depend on various factors like surface charge, particle size, porosity, shape and composition, surface functionality, crystallinity etc. These factors toxicity effect are described as:

Surface Charge: The surface charge of nanomaterials can produce cytotoxicity. Such as the positive surface charged nanoparticles have more interaction to the cells and leads to the cytotoxicity as compare to the neutral or negatively charged nanoparticles. However, the surface charge does not entirely represent the cytotoxicity but also depend on the surface Functionalization.

Particle size: The particle size of the nanomaterials is very much important for their effect. As the smaller size of particles easily cross the membranes of the cell and produced alteration in the cell leads to the toxicity. Thus the smaller particles are more toxic then the larger ones. The cellular uptake of nanoparticles is depending on the size due to its influence on the enthalpy and entropic properties that govern that responsible for the adhesion of nanoparticles with cellular receptors. The thermodynamic model showed the optimal cellular uptake with a ligand-coated nanoparticle having a size of 50 nm in diameter. In experimental studies with HeLa cells, spherical Mesoporous silica nanoparticles with a 50-nm diameter showed the highest cellular uptake.

In addition, a study using targeted gold nanoparticles reported the highest cellular uptake with 40–50 nm gold nanoparticles in SKBR-3 cells. The same trend was observed when the core was changed from gold to silver.

Porosity: The porosity of nanoparticles is also responsible for the toxicity. The more porous particle has imparted more toxicity. The impact of porosity on the toxicity level was identified by carried out in-vivo toxicity of SiO2 nanoparticles of different porosity ratios. The maximum tolerated dose (MTD) SiO2 nanoparticles increased in the following order: Mesoporous SiO2 (aspect ratio 1, 2, 8) at 30 – 65 mg/kg < amine-modified Mesoporous SiO2 (aspect ratio 1, 2, 8) at 100 – 150 mg/kg < unmodified or amine-modified nonporous SiO2 at 450 mg/kg. The adverse reactions above MTDs were primarily caused by the mechanical obstruction of SiO2 in the vasculature that led to congestion in multiple vital organs and subsequent organ failure.

One other evidence about acute toxicity with high doses of nanoparticles of three porous iron (ш) nanoMOFs having different structure and composition which was denoted by MIL-88A, MIL88B_4CH3 and MIL-100. In this MIL-88B_4CH3 bypass the BBB and reached to the brain but do not cause any severe cerebral toxicity. The reason behind crossing BBB was its hydrophobic nature and smaller size.

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