Nanotechnology is the study and control of matter on the nanometre scale. Nanoparticles are the results of chemical, biological and physical processes. Nanotechnology is an area of industry, development and research, which has been growing enormously fast especially in the last 10 years. Nanotechnology nowadays is being used in such important industries as construction, health care, energy conversion, the automobile industry, aerospace, chemical industry, textile industry and communication and electronics. Nanomaterials create new opportunities in industries, but they create health risks as well. People in the workplace can be exposed during production and usage of products, storage, transport etc. Nanomaterials also may affect the environment - water, soil, air, flora and fauna.
A series of expert publications provide details of the potential risks such as chemical, biological, physical and psychosocial. Nanoparticles can be produced by a variety of processes. According to the morphology, material from which nanoparticles were composed and the type, there exist the following categories: nanotubes, nanowires, nanocrystal and others. Nanotubes also known as carbon nanotubes are a carbon molecule, 1-2 nm in diameter. Nanowires are semi-conducting nanoparticles which are used in electron devices for electron transporting. Nanocrystal is a solid, structured molecule with a number of atoms between 1000 and 100000. Other nanoparticles are aggregated dendritic or primarily spherical forms of nanoparticles.
There exist four main methods of nanoparticles production: gas phase, synthesis of vapour deposition, colloidal and mechanical processes.
The gas phase process includes thermal plasma, microwave plasma, sputtering, laser ablation, high temperature evaporation, flame pyrolysis amongst others. The vapour forms in the process of aerosol reactors when exposed to high temperatures. This method is common for metal nanoparticles. Flame pyrolysis is the method whereby nanoparticles produced during flame heat initiates chemical reactions. The method is used for production of fumed silica and ultrafine. Furnace flow is the method to produce saturated vapour for particles, which at intermediate temperatures have a large vapour pressure. This method produces silver, galena and gallium nanoparticles. Laser pyrolysis is the process of nanoparticles produced during infra-red lasers quickly heating a flowing reacting gas. The method of plasma reactors used for energy delivery, which is the cause of evaporation of chemical reactions by achieving high temperatures of 10,000°C. Sputtering is another method of the gas phase, which occurs when high velocity ions of inert gas bombards a solid surface, which leads to vaporising materials.
The vapour deposition synthesis method of nanoparticles exposure based on the manufacture of semiconductors, which deposits silicon's thin films and other semiconductors on the wafers. An oxidation, pyrolysis, reduction and nitridation form vapours in a reaction chamber. These deposited films grow in several stages and the first atoms of the process deposit on the surface and forms small islands. The atoms then spread and merge in a continuous film, which forms a thicker film. The vapour deposition method produces nanoparticles from different materials.
The colloidal process is the method when different ions are mixed under the control of temperature and pressure, which form insoluble sediments. This is a simple example of nanoparticles production.
The mechanical attrition method produces nanoparticles from larger particles by grinding and milling. This method is common in the industry of clay, metals and coal.
Exposure to Nanoparticles
The types of exposure to nanoparticles are: inhalation, ingestion and dermal absorption.
Inhalation is the main route of nanoparticles entering the body. The respiratory system is the route for dust, which causes inflammatory reactions in the lungs. Some experts say that the inflammatory response of lungs depends on the particles' surface area remaining in the alveolar surface of lungs (“Nanoparticles: an occupational hygiene review”, Research report 274, p.12). Nanoparticle deposits in the lungs and the deposition factor increases because of the increase of the breathing rate and from switching to breathing through the mouth. From the lungs nanoparticles may be transferred to blood and from there to other human organs. Some nanoparticles can be deposited in the nasal area and can be transferred to the brain.
HSE of the UK estimates there to be 16,000 work-related skin diseases in 2008/9 and 19% of them are skin cancer. Harmful effects can happen within the epidermal and dermal layers and also can be transferred to internal organs, being absorbed by skin, via the bloodstream.
Ingestion happens when somebody unintentionally transfers nanoparticles from hand to mouth. This process can be accompanied by inhalation and may be swallowed through a mucociliary escalator
Nanotechnology is a new interdisciplinary area of research. Thus, all reviewed literature says that there exist many uncertainties of specific occupational health risks for humans. These uncertainties show a lack of knowledge in nanotechnology studies, which makes it difficult to predict health risks to the human body. This is a serious issue in such important areas as nanoparticles exposure routes, translocation in the human body and interaction of nanoparticles with the biological systems of the human body. Existing researches on animals and humans provides details, which is considered to be the basis for preliminary estimates for possible health effects from exposure to nanoparticles. Researches on rodents and cell cultures have demonstrated that the ultrafine particles are more toxic than larger particles of the same composition and substance, and causes pulmonary inflammation, tissue damage and lung cancer.
Although the amount of research done on the toxicity of nanoparticles is in short supply, enough has been done on the subject on the effects of inhalation of said particles. The three factors of particular relevance to us are the following:-
Nanoparticles are able to cross cell membranes and find their way into organs due to their size and it should be noted that they also have a high surface to volume ratio, meaning that more molecules may be present on any given surface and may explain why they can be more toxic than larger particles of the same composition.
Chemical composition and toxicity levels
The toxicity of nanoparticles depends not only on their chemical composition but also by other chemicals which are absorbed onto their surfaces. However, it should be noted that the damage potential can be reduced by modifying the surfaces of the nanoparticles.
The shape of nanoparticles also plays an important role in determining the amount of damage they can dispense. One example is carbon nanotubes, which are just a few nanometres in diameter but can be several micrometres long, highly toxic and work in a different fashion to the traditional model of toxic dust.
It is known that matter consisting of particles exists in air pollution, especially in emissions of vehicles and adversely affects human health, but it is not known in which way. Air pollution studies didn't prove that nanoparticles are more harmful than larger size particles. Particles in the respiratory tract can be transferred by inhalation. Inhaled nanoparticles can move through lungs by the bloodstream to other organs (brain, stomach, liver and possibly foetus). Literature reviews show a lack of information on these pathways, but it's known that the number of moving particles from one organ to another is significant and health effects from nanoparticles depends on the exposure time. Inhaled nanoparticles can be transferred through the mucous membrane inside the nose to olfactory nerve and even from there can move to the brain. Inhaled in the human body nanoparticles may cause lung inflammation and even heart problems. In vivo studies show that inhalation of diesel soot can cause general inflammation and can affect the cardiovascular system and heart rate.
Assessment and Control of Nanoparticles
Nanoparticles can be completely different from larger particles of the same material and interaction on biological systems can be different. That's why it's important to conduct risk assessments to reduce nanoparticles' effect on humans and environment. According to COSHH, industries in the UK that manufacture and use chemicals should conduct risk assessments. Risk assessments of nanoparticles should apply to: safety of employees and employers during the process of nanoparticles production; consumers' safety, who use the products that contain nanoparticles; local population's safety, who may be affected by nanoparticles produced from a local facility; environmental impact; risks to human health and environment during the disposal and recycling of nanomaterials. For a risk assessment of nanoparticles, it is important to specify chemical and physical properties of nanoparticles and their materials, taking into consideration accumulation of nanoparticles in the human body and environment.
The nanoparticles exposure control methods are:
* Elimination - eliminate the hazards
* Substitution - change high hazards on lower hazards
* Engineering - isolation and ventilation
* Administrative - Hygiene plans for chemical and work policy
* Personal Protective Equipment - gloves, clothes, respirators etc.
Existing methods of hazards identification, risk assessment and control of nanoparticles is not sufficient, because of a lack of knowledge in nanotechnology. The current risk assessment system and methodologies should be modified for nanoparticles to determine physical and chemical characteristics of nanoparticles assess hazards and find out the movement inside of human body and environment. In spite of enormously growing interest and publications in nanotechnology, there is a lack of information and knowledge on nanoparticles' characteristics, measurement, detection of movement, harm potential to humans and the environment.