May 25, 2007
The field of nanotechnology promises to impact our future significantly. Nanosized materials are used in numerous products already on the market, and many more are in development. Researchers project that nanomaterials may help us solve the energy and environmental crises and find a cure for cancer.
But these breakthroughs bring many unknowns. How will nanomaterials affect the human body? Will they harm the environment? Employees of companies who work with nanotechnology are asking, “Just what is this stuff?”
These questions dwarf the available answers. Yet as EHS professionals, we must protect workers from the potential risks these materials may present. With so much uncertainty, can we do our jobs?
The answer is yes.
Although much remains to be discovered about nanomaterials, this lack of knowledge does not release us from our duty to protect. And while it certainly presents a challenge to our profession, we can apply what we do best â€” hazard anticipation, recognition, assessment and control â€” to the little that we know about the hazards of these materials.
What is nanotechnology?Nanotechnology can be loosely defined as technology that uses engineered materials with at least one dimension measuring between 1 and 100 nanometers. These materials are created and manipulated at a molecular level. Within this broad definition, subcategories exist; two of the more common nanomaterials include carbon nanotubes and fullerenes, or “buckyballs,” which are usually a spherical arrangement of carbon atoms.
Other materials include nanoclays, nanofibers, and nanoplates. These materials all have many applications, and each application demands a specifically engineered nanoparticle.
It may also be helpful to distinguish what materials are not nanomaterials. For instance, many particles, such as volcanic ash, are created naturally and often fall into the same size range as nanomaterials. Fumes created by diesel engine combustion or welding activities also fall into this size range, but they do not fit the definition of nanotechnology.
These particles are categorized as ultrafine particles, a term that may or may not include engineered nanoparticles. What separates nanomaterials from these more randomly occurring particles is that they are engineered to have a specific atomic structure and to fall within a specific size range.
Guidance & regulationIn December 2006, the International Conference on Nanotechnology Occupational and Environmental Safety and Health took place in Cincinnati, Ohio. NIOSH, the University of Cincinnati and other contributors sponsored and organized this event. The conference brought together government agencies, EHS practitioners, laboratory managers, CEOs, toxicologists, labor, the insurance industry and academia to discuss the current state of knowledge and what the most pressing EHS problems are.
One consistent theme that attendees brought up was a perceived lack of guidance from government agencies on how to handle nanomaterials. NIOSH currently has a draft available for public comment titled, “Approaches to Safe nanotechnology: An Information Exchange with NIOSH.” NIOSH repeatedly stated its desire for industries to cooperate with them in sharing and coordinating research efforts.
OSHA representatives explained that while no specific nanotechnology standard currently exists, many of the standards currently in place apply to nanotechnology. Some of these standards include hazard communication, respiratory protection, personal protective equipment, the laboratory standard, permissible exposure limits, and OSHA’s general duty clause.
Nanomaterial propertiesMany nanomaterial properties differ between materials. But certain properties are commonly shared, and these may provide potential answers to our questions.
One property is the very high percentage of surface area in relation to the total mass of the particle. This means that even a very small amount of material may quickly and easily react with substances with which it comes in contact â€” including parts of the body, potentially causing harm.
Some nanomaterial properties can provide clues as to how we may be able to manage them in an occupational setting. Most researchers agree that these particles behave just like all other particles aerodynamically. Therefore, they will exhibit the same behaviors as many of the workplace contaminants we have previously encountered. This predictable behavior will also allow the application of many methods and controls we currently use to reduce risk.
Possible routes of exposureEvery common conceivable route of nanoparticle entry into the body is under investigation, but inhalation and dermal exposure have received the most attention.
Inhalation is of high concern because the particles are of respirable size, and they may become airborne during handling and/or manufacture. The particles’ reactive nature and large surface area make dermal absorption a possibility. Some studies have also shown that if exposed to skin, nanoparticles can accumulate in small folds, such as the underside of the knuckles, or they may penetrate the skin.
Exposure evaluationThe industrial hygiene community has debated how to best quantify exposure to nanomaterials. Most occupational exposure limits (OELs) for particulate are expressed in terms of a mass-based concentration such as mg/m3. But because of nanomaterials’ high surface area, a very small mass of material may produce very different effects than those of a more traditional size. For that reason, many professionals are questioning whether traditional OELs based on ppm or mg/m3 are appropriate measurements for nanomaterials.
How to measure these exposures is under debate, but consensus has not been reached mainly because of the lack of knowledge of nanomaterial toxicology. Some have suggested that new OELs based on measured or estimated surface area be used rather than mass-based concentration, while others have suggested that particle counting may provide a more accurate indicator of exposure. However, there is currently much debate in the scientific community and it is unlikely that any definitive method of exposure assessment will be available soon.
One way to evaluate nanomaterial exposures that is currently available would be to use tracer gas technology. Tracer gas is used as a surrogate for the nanomaterial. The gas is released at the source in a known concentration. Measurements of tracer gas concentrations are then taken in the area of the workers breathing zone to determine the concentration of gas that has escaped the source and any engineering controls in place. From this information a quantitative exposure result can be determined.
Nanomaterial controlThe hazards nanomaterials present are largely unknown at this time, but that should not prevent us from taking action to protect employees in the workplace. Just as we manage many other materials with unknown hazards, we can manage this one. Put very simply, by eliminating exposure, you eliminate the risk to employees.
The ideal way to accomplish exposure control is through a completely closed process where all aspects of nanomaterial manufacture are contained. Some considerations for this may include glove boxes or other enclosed devices where employees can manipulate the material without being directly exposed. Designing and installing a closed process system is the most costly method of hazard control initially, but with proper maintenance, it is also the best way to reduce employee exposure to any materials with unknown hazards.
Where the handling of nanomaterials is unavoidable, some form of protection against inhalation and skin contact with the material must be used. This may be best accomplished by effective local exhaust ventilation. Again, because these small particles behave like gases in air, a well-designed local exhaust ventilation system can remove contaminants from the breathing zone. Often, work can be performed in a laboratory hood or similar device. In other cases, a small, movable exhaust system can be used.
When designing a ventilation system, the capture method is critical. While some questions remain as to the efficacy of filters currently in use, it is generally accepted that HEPA-type filters (i.e., 99.97% efficient at 0.3µm) will capture particles in the nanosize range. Because particles can be captured in a filter by many different methods (e.g., impaction, electrostatic forces, Brownian motion, etc.), these filters are likely effective. Super Ultra Low Penetration Air (SULPA) and ULPA filters are also available that capture particles at efficiencies of 99.9999% and 99.999%, respectively.
Like any other engineering controls, closed systems and local exhaust ventilation must be properly maintained and evaluated periodically. Standard methods of control evaluation are still valid. For a quantitative result of the capture efficiency of a system, a tracer gas, such as sulfur hexafluoride, can be used. Several standard methods exist for performing these evaluations. Smoke tubes and/or air velocity measurements can be used to give a qualitative indication.
Other types of controls such as PPE will likely be necessary and should be selected based on the specific exposure. As always, employee training is essential. Proper work practices must be followed. This includes slowly and carefully handling the material, taking care to allow as little of it to become airborne as possible. It also includes the proper maintenance and use of personal protective equipment. Also, maintenance employees who may also enter these work areas will require different work practices and training.
Finally, other methods can be used to reduce exposures. Administrative controls, such as reducing an employee’s time in an area with potential exposure, are one option. Traditional methods of dust control can also be utilized. For example, “wet methods” like solutions or slurry can prevent particles from becoming airborne.