The critical question based on the little information available pertains to the assessment of hazards and risks. The unifying theme is that nanoparticles are smaller than their bulk counterparts but have a larger surface area and particle number per unit mass; these characteristics generally increase toxic potential as a result of increased potential for reactivity The application of that theory to the whole of nanotechnology rather than to specific particles and processes may increase rather than decrease the uncertainty about hazards and risks.
Increasingly, other characteristics e. These characteristics are tremendously variable. Consequently, it is useful to put some limits on the uncertainty by being more precise in the language used to describe nanoparticle hazards and risks. Knowledge about hazards and risks. Health effects data on workers involved with nanotechnology are limited because of the incipient nature of the field, the relatively small number of workers potentially exposed to date, and the lack of time for chronic disease to develop and be detected.
Nanotechnology and the environment - Hazard potentials and risks
Ultrafine and fine particles have been assessed in epidemiologic air pollution studies and in studies of occupational cohorts exposed to mineral dusts, fibers, welding fumes, combustion products, and poorly soluble, low-toxicity particulates such as titanium dioxide and carbon black 25, The hazards of these exposures and exposures to engineered nanoparticles are also identified in animal studies 27, 23, 28, 29, 30, 31, 32, A strong relationship exists between the surface area, oxidative stress, and proinflammatory effects of nanoparticles in the lung.
The greater the oxidative stress, the more likely the risk of inflammation andcytotoxicity 26, The findings from animal studies ultimately need to be interpreted in terms of the exposure dose that humans might receive. Although there is still some debate, the evidence from air pollution studies associates increased particulate air pollution the finer particulate matter fraction, PM2. Moreover, the concentrations associated with measurable effects on the health of populations are quite low In occupational studies, the populations that are repeatedly exposed to hazardous mineral dusts and fibers in the respirable range e.
With asbestos, the critical risk factors for developing respiratory diseases are fiber length, diameter, and biopersistence. For poorly soluble, low-toxicity dusts such as titanium dioxide, smaller particles in the nanometer size range appear to cause an increase in risk for lung cancer in animals on the basis of particle size and surface area 36, 31, Although the findings are not conclusive, various studies of engineered nanoparticles in animals raise concerns about the existence and severity of hazards posed to exposed workers Possible adverse effects include the development of fibrosis and other pulmonary effects after short-term exposure to carbon nanotubes 30, 31, 32 , the translocation of nanoparticles to the brain via the olfactory nerve, the ability of nanoparticles to translocate into the circulation, and the potential for nanoparticles to activate platelets and enhance vascular thrombosis None of these findings are conclusive about the nature and extent of the hazards, but they may be sufficient to support precautionary action.
Ultimately, the significance of hazard information depends on the extent to which workers are exposed to the hazard.
Nanotechnology Environmental Health and Safety
This is the defining criterion of risk the probability that an exposed worker will become ill. A need has been identified for nanoparticle-specific risk assessments i. Risk assessment has been widely used to manage the uncertainty of risks posed to humans by newly introduced chemicals or processes. However, nanotechnology encompasses a diverse range of compositions, structures, and applications, so a single risk assessment and management strategy may not be appropriate Nanotechnology involves the manipulation of matter at the nanoscale to produce materials, structures, and devices that contain various particle types, sizes, surface characteristics, and coatings.
These particles may best be addressed by a range of risk assessments specific to the type of particle composition, surface characteristics, and shape being assessed. Because of the general inverse relationship between particle size and surface area, doseeffect relationships may vary as a function of total surface area and number of particles rather than mass units 8. Risk assessments will be useful to the extent that they reflect the effects of particle sizes and surface area, but such assessments may also need to reflect other particle characteristics.
Moreover, it is currently unclear the extent to which the toxicokinetics an important component in risk assessment can be predicted from knowledge of physicochemical properties of nanoparticles 8. Evidence base for hazard controls. The most frequently used model of the workplace environment identifies sources of hazards and routes of exposure e.
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Control can be introduced at each of these points. Occupational safety and health professionals have identified a hierarchy of controls based on reliability, efficiency, and the principle that the environment should be controlled before the worker is required to take any preventive action In its simplest form, the hierarchy of controls specifies that engineering controls including substitution, enclosure, isolation, and ventilation are preferred to the use of personal protective equipment such as protective clothing and respirators.
Work practices are frequently incorporated in risk management efforts to minimize worker exposures, and they often supplement the use of engineering controls. Administrative controls such as worker rotation are sometimes included and generally constitute the "third line of defense" when engineering controls and work practice controls cannot achieve the desired level of worker protection In the absence of adequate toxicity information and extensive history of engineered nanomaterials use, the rationale for control guidance has been based on experience in controlling exposures to incidental ultrafine particles and gases.
A rich history of aerosol science describes the fundamental properties of aerosols and their control 42, 43, 44, 45,46, 47,48, Although ultrafine particles are considered equivalent to nanoparticles by some authorities 8 , they are usually but not exclusively at the upper end of the nanoscale range. If airborne nanoparticles conform to the classical physics and aerodynamics observed for larger particles, then controls effective in capturing fine and ultrafine particles and gases such as source enclosure, local exhaust ventilation, and personal protective equipment should be effective with the current generation of nanomaterials.
It is reasonable to believe that most control methods used for fine and ultra- fine particles and also for gases will be useful for controlling nanoparticles, but there is no reason to expect that application of these methods to new nanoparticle generation processes will result in better control than that previously demonstrated for microscale powders and gases A considerable body of opinion indicates that the adverse effects of nanoparticles cannot be predicted or derived from the known toxicity of bulk materials with similar chemical composition and surface properties 8.
Control options for nanoparticles range from no controls to the use of isolation and containments practiced with radiation, gases, and biological agents. The question is where in this continuum should controls be selected. This may also translate into how much money to invest in them. When risks are known to be high or low, the decision is relatively easy, and the appropriate control strategies are generally apparent.
However, when hazards are uncertain as they are with nanoparticles , the difficulty is in deciding what level of controls is warranted Figure 1. Summary of evidence on hazards and controls. The evidence base pertaining to nanotechnology hazards and controls has been reviewed in various publications 4, 25, 12, 5, 52, 8 and is summarized in Table 2 by four categories of knowledge described in terms of hazards and controls and awareness. These categories are mutable and pertain to the state of knowledge at a given time.
Category 1 "what we know we know" indicates that we have some knowledge about the health hazards posed by some types of nanoparticles e. This category applies to the current generation of engineered nanoparticles and is the basis for much of the current guidance. Category 2 knowledge "what we know we don't know" is the basis for much of the research currently being conducted or planned. In general, we do not know much about the hazards of new or anticipated engineered particles or whether enough precautions have been taken. A major question is not only how to control exposure but also what are the appropriate extent and cost of controls.
Category 3 knowledge "what we don't know we know" represents the under-utilization of established knowledge.
That is, scientists have had extensive experience in hazard and exposure control for ionizing radiation, biological agents, pharmaceuticals, grain and mineral dusts, and air pollution. This experience could be more directly brought to bear on controlling the hazards of nanomaterials in the workplace. In addition, this category could include proprietary information about nanoparticles that is not available for hazard assessments. Category 4 knowledge "what we don't know we don't know" represents a perennial area of philosophical exploration This category includes the range of scenarios about the potency of hazards and the extent of risks.
Will new scenarios present new types of exposures and risks? The popular literature on nanotechnology is replete with characterizations of possible future scenarios, but no projections have been made of workplace hazards and risks 54, Category 4 knowledge also includes the lack of awareness of factors influencing an issue.
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This lack of awareness can be addressed by engaging a wide variety of disciplines and communities of interest to characterize an issue 1. Category 4 knowledge also includes the beliefs we hold that may be wrong.
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Such beliefs could lead to taking or not taking protective measures on the basis of faulty assumptions. Eventually, Category 4 knowledge can be transformed to Category 2 and then to Category 1. Regardless of which type of knowledge is considered, the ultimate ethical requirement is to accurately portray the state of knowledge about a hazard or risk and not to understate or overstate it. However, given the developmental nature of nanotechnology, the knowledge of hazard potential will change over time and require restatement and possibly modification of guidance. In the absence of adequate hazard and risk assessment data, the critical question is how much caution is warranted.
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Identifying and communicating hazards and risks. The "hazard identification" stage of risk analysis is the basis for risk management decisionmaking. The output of this stage is often highly debated, since the process of reasoning is primarily qualitative and the results trigger other stages of analysis and decisions about preventive action Interpreting scientific information about the hazards of nanomaterials is basic to communicating the hazards and risks posed to workers. Interpreting and communicating hazard and risk information is an integral part of risk management by employers.
The employers' decisionmaking will focus on deciding which preventive controls should be used to assure a safe and healthful workplace.
Employers and workers look to scientists and authoritative organizations to help interpret hazard and risk information and to put it into context. This expectation may pressure scientists to go beyond the mere conduct of research. The interface between science and morality is exceedingly complex, but scientists are generally considered to have ethical obligations to society at large 57, 16, However, no consensus has been reached about the nature of those ethical obligations beyond fulfilling the professional responsibilities internal to scientific research.
Framing a clear and coherent approach to the ethical responsibilities of scientists in nanotechnology is a difficult task. At the least, such an approach requires scientists to use appropriate qualifiers in published papers and to be cautious in generalizing their results. More broadly, it means not shrinking from considering the implications of their work, even if all the scientific details are not known.
Decision makers may have inadequate scientific information to help them decide how precautionary their approach should be To determine whether a decision conforms with the principle of nonmaleficence, decision makers must determine the harm that could occur if the nanoparticles were as toxic as suggested by preliminary hazard information.
Data on air pollution and industrial ultrafine particles indicate that a given mass of nanoparticles would be more biologically reactive and hence potentially more toxic than the same mass of larger particles Ultimately, the more stringent level of controls may result in risks that are equal to or smaller than risks posed by larger particles.
Authoritative organizations and employers are responsible for communicating the risk workers face after appropriate controls are implemented. Failure to do so may preclude workers from exercising autonomy.
This issue may be confounded by the fact that the employer has a proprietary interest in not releasing information about "nanoproducts" and workplace controls.