Essay title - Nanomaterials Risk Safety
Abstract
Nanomaterials are now being manufactured and are already reaching the market in a wide range of consumer products. Nanomaterials exhibit unique physical and chemical properties and are engineered to exhibit magnetic, optical and electrical properties. Preliminary evidence from experimental research studies indicate the possibility of nanomaterials to penetrate and cause damage to human tissues and cells. This report gives a toxicological perspective, outlining possible routes of uptake by humans, environmental concern and discussing some of the difficulties issues that policy makers such as the Unites States Enviromental Protection Agency (EPA) have to grapple with in addressing known or suspected toxic effects posed by nanoparticles on biological system and the enviroment, and the practical effect for human health risk assessments, and safety measures.
1. Introduction
Nanotechnology is defined as the understanding and control of matter at dimensions between 1-100 nanometers, in which unique phenomena enable novel applications. Engineered nanoparticles have become an efficient class of new materials with many applications that make them extremely useful for commercial development. Nanoparticles have been increasingly used for manufacturing a wide range of industrial products such as cosmetics or clothes and for infinite applications in electronics, aerospace and computer industry.
Nanotechnology has the potential ability to dramatically improve the effectiveness of a number of existing consumer and industrial products and could have some impact on the development of new materials ranging from disease diagnosis and treatment to environmental consideration. The use of nanotechnology has made it possible for more reactive intermediates in industrial processes and has a dual potential as powerful reaction catalyst to induce chemical reactions with reduced energy input. These applications offers the ability of nanoscale materials to enact the performance of a wide variety of products and services including sports equipments, textiles and fabrics energy generation and distribution, drug and medical devices, and food processing. Due to the unique physico-chemical properties of nanoscale materials, research has been initiated at private and public organizations to develop measures for evaluating human health implications from exposure to these materials.2
The processes used in the manufacture of nanomaterials plays an important role in particle release. In association with the quality, speed or cost there are a wide range of processing methods that are used in the manufacture of nanomaterials. These processes can be classified under two major categories, namely bottom up and top down.3
In the bottom-up manufacturing process the nanomaterial and structures are configured atom-by-atom or molecule-by-molecule and this induces the precussor material to grow in size. Chemical synthesis, self assembly, and position assembly are the three most important approach to this method.
Any physical phase is changed in accordance with the particular process during the chemical synthesis of the material. Production of nanoparticles are through a chemical reaction, with or without the application of the external agents, in order to generate the desired material. For this type of manufacture method, a further change in the phase state of the nano-product might be taken into consideration, namely the solid state for the collection and application of the material.
The atoms and molecules are self arranged into ordered nanoscale structures through chemical and physical interactions between the participating units in the self assemble method of bottom-up production. This method of production is the most economical due to lower energy consumption and waste; it is however still in a rudiment stage because of the present lack of understanding of the thermodynamic and kinetic processes on the nanoscale. The current process is associated with the use of an external force to achieve the intended production volume by speeding up the rate of the process.
The position assembly technique is not economically suitable for mass production, it is however very useful in the production of nanomachines and nanorobots. There is a deliberate manipulation of the atoms and molecules which are placed one-by-one to achieve the desired characteristic for the intended use. This method of production uses optical tweezers to place the atoms in the desired position. The ability of the fabrication tools and microscopes, like the scanning probe microscopy, challenges the precision placement of the atoms enabling it to be economically unfeasible. But the anticipated feature of producing self-replicating nanorobots makes it a notable technique with a superior end product.4
Top-down manufacturing approach involves the production of nanomaterials from its bulk material by removing the excess material through etching, milling and machining. Techniques like precision engineering and lithography are related technologies, which are mostly used for manufacturing the nanoparticles in top-down manufacturing approach. Comparing top-down approach to bottom-up techniques, energy consumption and waste are greater for the later. Irrespective of this limitation, this is the most preferred technology for nanocomponents. The lithographic techniques, using short wavelength optical sources is the most common top-down approach to fabrication. An important advantage of the top-down approach as developed in the fabrication of integrated circuits is that the parts are both patterned and built in place, so that no assembly is needed.4-5
Nanoparticles are defined as particles with at least one dimension or small scale substances less than 100nm with unique properties and thus exhibiting complex exposure and health risk implications.6-7
Human and other beings have been exposed to airborne nanosized particles through out their evolutionary stages. There has been a dramatic increase to exposure to nanoparticles over the last century due to anthropogenic sources such as internal combustion engines, power plants, and many other sources such as thermo-degradation. The rapidly developing field of nanotechnology has become yet another source through inhalation, ingestion, skin uptake, and injection of engineered nanoparticles. For human beings the portal of entry routes are via the lungs by respiration, via the skin by dermal exposure and via the gut by ingestion of food and drink. It is a well known fact that the effects of asbestos fibres, monofibres are particularly identified as health hazards. However, their impact will depend at least on their dimensions which include surface area and on their surface composition and reactivity; i.e. on their properties as nanomaterials. This underpins the fact that the health implication of nanomaterials, along with the other properties that define them as nanomaterials, depend on their size and surface area.8-9
There is a potential benefit for Nanoparticles to travel through the organism than other materials or larger particles. The effect posed by the interactions of nanoparticles with fluids cells and tissues need to be taken into consideration, starting at the portal of entry and then via a variety of possible pathways towards target organs.10
Apparently, in stark contrast to the divers efforts aimed at exploiting desirable properties of nanoparticles for developing human health, there is a boiling desire to evaluate potential undesirable effects of nanoparticles when applied for medicinal purposes, or after unintentional exposure during production or processing for industrial applications. The potential benefits that make nanoparticles so attractive for advancement in nanomedicine and for specific industrial processes could also prove toxic when nanoparticles interact with living cells. The evaluation of the safety of nanoparticles should be of prominent significance as a result of their widespread distribution for industrial applications and the possibility of human exposure, directly or through release into the environment (air, water, soil).8
Nanoparticles are however produced by natural phenomena, and by many human industrial and domestic techniques, such as cooking, material fabrication and transportation, making use of internal combustion and jet engines and unintentional release of nanoparticles into the atmosphere. Over the past decade different sources of nanoparticles have been introduced, within the context of intentionally engineered nanoscale components of consumer products and advanced technologies. There is however, no clear information on how important is the increase in exposure to nanoparticles associated with this new products either in the workplace or in the context of consumer of nanotechnology-based products. 11
There are quite a lot of information on the hazard (toxicology) of nanoparticles that are accidentally produced, rather less on manufactured nanoparticle like carbon black and very little on the specialized nanotubes and nanoparticles produced for nanotechnological purposes. The challenge posed for toxicologists is to determine if the knowledge available for the accidentally produced and bulk manufactured nanoparticle is transferable to the engineered nanoparticle.
The toxicokinetic model, often termed ADME (Adsorption, distribution, metabolism and excretion) should be an important factor to be taken into consideration for the quantitative studies of nanoparticle .Though, this is based on classical chemical toxins, it can also apply to particles. An important information provided by toxicokinetics is about the dosimetry for toxicology studies by predicting realistic doses that can be expected at channels of entry and target organs. It is important to use plausible doses and indeed good toxicokinetic may include some organs as target for effects of the toxin since the predicted doses may be negligible. A toxicokinetic profile of any nanoparticle is however important to be obtain as this covers all of the above as well as the fate of the particles in being changed and excreted.12
The chemical composition of the nanoparticles, characteristics of the products made from them, or the manufacturing processes that are used to generate them may be one of the side effects experienced by the use of nanotechnology. The large surface area and the associated increased reactivity of some nanoparticles may enhance broad transport in the environment as a result of greater persistence, or they may impact biological systems from interactions with cellular materials. When placing emphasis on nanomaterials, size should be taken into consideration and could facilitate and exacerbate effects caused by the composition of the materials themselves.
There has been quite a number of research and reports on inhalation and dermal exposure to nanoparticles and other ultrafine particles. However, the current research on ultrafine particles may not be applicable to the evaluation of the safety or risk from manufactured nanoparticles because the ultrafine materials that have been studied are neither a consistent size nor pure in chemical or structural composition.
In other to identify validated methods and techniques for characterizing and testing nanomaterials more research need to be done that will generate risk assessments and safety evaluation. In addition, data that will helps to elucidate the mechanisms of action for these materials will provide more insight into the hazards associated with them. Exposure data characterizing realistic exposure scenarios for nanomaterials are essential for the development of risk assessments that will adequately inform public health decision making.13
Policy makers such as the United States Enviromental Protection Agency (EPA) are now faced with the challenge of finding more effective information about the exposure and fate/transport data of nanoparticles, initiating appropriate risk assessment/management strategies, and seeking appropriate pollution prevention and environmentally favourable techniques for the technology, development of novel treatment and remediation technologies using nanotechnology, a proper understanding of the health and environmental implications of intentionally produced nanomaterials.14
This report gives a toxicological perspective, outlining possible routes of uptake by humans, environmental concern and discussing some of the difficulties issues that policy makers such as the Unites States Enviromental Protection Agency (EPA) have to grapple with in addressing known or suspected toxic effects posed by nanoparticles on biological system and the enviroment, and the practical effect for human health risk assessments, legislation and safety measures.
2. Portal of entry of Nanoparticles and the need for more Research by EPA.
The respiratory system, central nervous system, gastrointestinal tract and skin have been potential route for the penetration of nanoparticles into the body.
Biokinetic and toxicokinetic pathway of nanoparticles
Research studies have proofed that particles within the nanoscale range have the potential ability of entering the body via pulmonary and intestinal routes 15-21 (there is presently no concrete evidence of dermal penetration12). The portal of entry in all the three cases is dependent on the particle size as well as the surface properties. The physico-chemical properties of nanomaterials that make them unique, leave open the possibility that they could pose adverse effects on health and the environment.
The method to addressing the safety of nanoscale materials will best be conducted via multidisplinary groups. Since this suggestion may not be relevant to toxicology, critical examination of the safety of nanomaterials will require support from the chemists who invented them due to the important role that full material characterization will play in the interpretation of the studies to address hazard and characterize exposure.13
Wiebert et al., 2006 proofed in his study that ultrafine particles were not retained in healthy and affected human lungs.22 Thich is a contrast to previous studies revealing the rapid and substantial uptake of ultrafine particles in the lungs. His work proofed no evidence of quantitative (mass-based) translocation of 100-nm particles to the systemic circulation from either healthy or affected lungs. There is therefore a need for policy makers like EPA to undergo more research to fully certify if a few per cent of translocated particles is sufficient enough to cause harmful effects.
The conventional hypothesis that the toxicity of nanoscale particles is dependent on particle size and surface area have been proofed contrary in the study carried out by Warheit et al., 2006 whose result revealed for the first time that nanoscale particles types, were not more cytotoxic or inflammogenic to the lung as compared to larger sized particles of similar composition18. It is however, necessary for more research to be conducted by EPA to ascertain the possibility of particle size and surface area in producing lung toxicity before a concrete conclusion can be made.
3. Need for more Research efforts by EPA in Developing Improved Data for Nanomaterial Risk Assessments.
EPA and other research agencies are now examining critical research needs for the development of risk assessment for nanomaterials.
The entire
Adapted from “Toxic effects of nanoparticles and nanomaterials: Implications for public health, risk assessment and the public perception of nanotechnology”. HEALTH, RISK & SOCIETY. JUNE, 2007.
A brief summary of the research needs by EPA in addressing the risk assessments of nanmaterials is listed below. A more detail information of EPA’s draft nanotechnology research needs can be found in EPA’s draft Nanotechnology White Paper. http://www.epa.gov/osa.
Chemical Identification and Characterization of Nanomaterials.
In order to fully assess the risk posed by nanomaterials, the identification and characterization of chemical substances and materials should be given first priority. It is however not yet clear if physicochemical testing methods are adequate enough to sufficiently characterize nanomaterials in order to evaluate their hazard and exposure and assess their risk. The research need in this area includes the compilation of data on the distinct chemical and physical charcteriatics of nanomaterials, with critical emphasis on the effect of particle size and size distribution, morphology, charge, and surface coatings on reactivity, toxicity and mobility14.
Ecological effects and Enviromental Fate and Transport in Air, Soil and Water.
There are still uncertainties about the effects of nanoscale particles on the enviroment and even non-human species. The exposure of organisms like daphnia, fish and rats to nanoparticles and observing the dose or concentration of the measured morbidity have been the conventional toxicological approach to assessing ecotoxcity. The results from the assessment is then scaled up to give a rough prediction of human toxicity. The observation of the effects of a pollutant on cells in culture happens to be an alternative approach, this is still at an explanatory stage and the in vitro test is yet to be performed. Another proposed approach is the in silico approach which aim assesses the toxicological potential of chemicals by computer calculation of quantitative structure.9
( Oberdoster, 2004 ) reported a study on the effect of fullerene, C60 to induce oxidative stress in the brain of juvenile largemouth bass stating that nano-sized particles are able to translocate into the brain via the olfactory bulb.23
The ability of nanoparticles to penetrate the earth crust, traveling large distances underground makes it a useful tool for the assessing of variations in the environment and ecosystem. However, they may also have detrimental effects like damaging the earth crust thus inducing geothermal disturbances.4
The environmental concern for exposure to nanoscale particles have reported to come from two main areas: (1) the absence of technology in sewage treatment works for the specific removal of engineered nanomaterials from waste water, and (2) the safety of new nanotechnologies that may be used by the water industry.24
There is a growing need for more research on the transportation and potential transformation of nanomaterials in soil, subsurface water, surface water, water treatment systems, and the atmosphere. Additionally, there is an environmental fate research need to effectively ascertain the factors that induces the fate, transport, and transformation of engineered nanomaterials in ecosystems, finding out under what conditions nanomaterials bound to products are released into surrounding environmental media, understanding mobility characteristics of engineered nanomaterials, and researching by what mechanism and in what form engineered nanomaterials transition from one environmental media to another.14
Exposure assessment
Workers have been exposed to nanomaterials during the production and the use of these materials. Combustion Derived Nanoparticles (CDNP) such as, welding fume and nanoparticulate carbon black, which are both examples of occupational hazards, coal fly-ash which is an environmental hazard and diesel soot which is both an environmental and an occupational hazard have been known to be toxic following inhalation exposure.25
Exposure research needs include determining the nanomaterial properties that have the potential for toxicity this include (particle size/size distribution, surface/volume ratio, shape, electronic properties and surface characteristics). There is also a need to adequately determine the proper functioning of personal protective equipments (PPE).
Human health effects Assessments
Studies on the toxicity of nanoparticles and the effects on human health have been reported by several scholars and research groups. The respiratory system, skin, gut, blood and central nervous system, have been reported as potential route of uptake of nanoparticles.
There is a research need to critically assess which type of nanomaterial has a high commercial potential for dispersive applications in order to create a channel for priority-toxicity testing and to determine the potential health effects (local and systemic: acute and chronic) resulting from direct consequences of exposure to either nanomaterials or their by-products. A detection of the properties of nanomaterials that are most predictive of toxicity to receptors is also necessary.14
Conclusion
Government research organization should also not relent in their effort in evaluating the utility of existing testing and measurement methods for the safe evaluation of nanomaterials.
References
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