Nanotechnology - Environmental Health and Safety Considerations
By Keith Rickabaugh and Randy Ogle, CIH, CSP, CHMM

Abstract:
Engineers and scientists are actively working on developing tools and procedures to create and utilize materials that have critical dimensions that are less than 100 nanometers in size. These materials contain nano-particles that are on a scale so small that they may only be individually characterized using high end laboratory instrumentation, such as an electron microscope. The excitement surrounding current nanotechnology endeavors for scientists and business people revolves around the notion that unique material properties can be realized. In addition, discoveries made in the nanotechnology fields may be patentable and have applications across many disciplines.

Industrial hygienists, safety personnel and environmental professionals are faced with challenge of keeping pace with nanotechnology developments. The use of engineered nano-particles in the workplace creates many questions related to potential risks to workers and the environment. Many of these questions need to be currently addressed in the absence of specific nano-particulate regulation, information regarding known risk, and standardized measurement methods. With the on-going concern of industries' need to minimize costs, manage budgets and protect workers, EH&S personnel are faced with a challenge to implement and justify their nanotechnology specific programs.

There is a possibility that conformance with current regulatory standards and guidelines may not be enough to address the needs of nanotechnology industries. As a result, EH&S personnel are encouraged to employ the use of commercially available technologies and work practices to manage engineered nano-particles. In the absence of perfect information, cost-effective prudent practices should be implemented to enhance the control and measurement and nano-particles. Building upon what we know today, it is believed that it is possible to work with engineered nano-particles in a safe and efficient manner. This article outlines some of the issues and guidelines for EH&S personnel consider when recognizing, evaluating and controlling potential exposures and potential environmental releases related to nano-particles.

ARTICLE:

Nanotechnology: Environmental Health and Safety Considerations

Practical Suggestions for Assessing Exposures

By Keith P. Rickabaugh and Randy Ogle

Engineers and scientists are developing tools and procedures to create and utilize materials that have critical dimensions less than 100 nanometers in size. These nanoparticles are so small that they can be characterized only by using high-end laboratory instrumentation, such as an electron microscope. The excitement surrounding nanotechnology revolves around the notion that it can realize unique material properties. Discoveries made in the nanotechnology fields may have applications across many disciplines.

People are exposed to nanoparticles every day from environmental soots, common commercial products, and other materials. As new nanomaterials are developed, business managers, engineers, scientists and environmental safety and health (ESH) personnel will have to communicate closely about work activities and safety issues. The toxicity of nanoparticles depends on many factors, including chemistry, morphology, and surface charges, and probably relates to particle surface area (especially for insoluble or low-soluble particles). Exposure to nanoparticles can trigger allergic asthma symptoms or aggravated symptoms of pneumonia, and may also affect cardiac or circulatory systems.

Understandably, industry does not want to overreact to safety concerns. People should not scramble to don personal protective equipment (PPE) every time they use suntan lotion, write with ballpoint pens, light campfires or apply certain cosmetics. But we need to protect society from the known or suspected health risks of engineered nanoparticles while meeting needs for products that take advantage of advances in nanotechnology.

While the use of engineered nanoparticles in the workplace results in potential risks to workers and the environment, IH and EHS personnel lack specific engineered nanoparticle regulations, information regarding known risks, and standardized measurement methods. Other challenges include industries' need to minimize costs and manage budgets.

Conformance to current regulatory standards and guidelines may not be enough to address the needs of nanotechnology industries. As a result, EHS personnel are encouraged to use commercially available technologies and work practices to manage engineered nanoparticles. Prudent, cost-effective practices will enhance the control and measurement of nanoparticles, despite the absence of regulatory information. Currently available information allows for the safe and efficient handling of engineered nanoparticles. This article outlines some of the issues for EHS personnel to consider when attempting to minimize or eliminate potential exposures and environmental releases of nanoparticles.

The Industrial Hygiene Approach

Today's industrial hygiene professionals do not have a complete set of knowledge for recognizing, evaluating and controlling the hazards of engineered nanoparticles. In addition to workplace safety issues, IH and EHS staff must evaluate the risks of intended applications related to nanoparticles.

Many engineered nanoparticles are intended to be ingredients in the formulation of other substances, such as composite materials. As new materials are developed, the properties of the materials and production processes could change. Therefore, EHS staff need to consider the work processes used to produce products and the intended use of engineered nanoparticles. Questions when dealing with nanomaterials include the following:

Are the engineered nanoparticles persistent in the environment?
What are the potential exposure pathways to workers, handlers and consumers?
How should materials be contained to reduce the potential for exposure?
How can engineered nanoparticles be detected and measured in the workplace?
What environmental issues are associated with possible releases of engineered nanoparticles?
What is the proper method to dispose of engineered nanoparticles or materials that contain engineered nanoparticles?

EHS professionals should understand that nanotechnology refers not to a specific type of material but to a method of using applied sciences to produce and modify materials on an increasingly small scale. The nanotechnology industries are interested in taking advantage of chemical and physical properties of nanoscale substances. EHS professionals will have information gaps when attempting to reference current exposure limits to measurements obtained using traditional sampling methods. Expert judgment is necessary to determine whether potential exposure-related concerns have been adequately addressed.

Health and Safety Guidelines

Site- and material-specific health and safety guidelines must be based on the chemical and physical characteristics of engineered nanoparticles and should relate to the work practices and applications of the materials. Professional judgment and site-specific measurements or modeling of potential exposures and risks should inform the guidelines. Guidelines should vary depending on the application, stage of processing or handling, and ultimate use of the substance, and should be reviewed and updated as additional information becomes available.

The U.S. Department of Energy, NIOSH, ASTM^(1-3) and others have provided guidelines that can protect workers. Many of these approaches are based on preventative measures that have been effective engineering controls and work practices for naturally occurring or manmade materials such as asbestos, carbon black, welding fume and ultra-fine titanium dioxide. The engineering controls, work practices and measurement techniques suggested for evaluating and controlling insoluble unbound (i.e., well-dispersed) or bound engineered nanoparticles are based on a wealth of knowledge that already exists in the EHS communities. Some precautionary measures include the following:

Developing descriptions of work with input and review by workers and safety experts
Providing safety awareness training
Proper labeling to communicate potential hazards
Containerizing substances to prevent material loss and mitigate the potential for accidental releases
Handling materials in limited quantities (that is, use only what is needed)
Working with nanoparticles suspended in a liquid medium to minimize aerosolizing materials
Maintaining good housekeeping procedures and immediately cleaning up spills using appropriate work practices and methods (for example, use of wet methods and HEPA-filtered vacuums)
Using disposable supplies for handling or containerizing materials
Working in well-ventilated areas that employ negative pressure methods or directional flow HEPA-filtered technologies
Limiting access to work areas or materials to trained workers
Using personal protective equipment (for example, clothing, eye protection and respirators)
Implementing measurement methods such as air sampling to qualitatively and/or semi-quantitatively assess worker environments
Properly disposing of or encapsulating engineered nanoparticles that are no longer needed
Continually supervising, reviewing and updating procedures and work practices as additional information and materials become available

Although PPE can reduce workers' exposure, it should be a last line of defense. Appropriate work practices and engineering and administrative controls should be evaluated prior to requiring PPE.

Expert decision making is necessary to recognize exposure risks and implement appropriate responses. Protective measures need to be effective, reasonable, practical and efficient without compromising safety. For work processes that require special considerations, ESH personnel must first understand which responses are effective and then focus on efficiency goals.

Air Sampling Considerations

Operations involving engineered nanoparticles might liberate particles in the air that could be inhaled or released into the environment. Few exposure limits are available for reference, but we must monitor exposures and environmental releases to understand their magnitude and the efficacy of our controls. Researchers should develop an understanding of the dose response for nanomaterials. Air sampling methods and strategies will vary depending on the type of material, the work environment and nature of the operation being investigated.

Questions concerning air sampling for nanoparticles include the following:

Can unique characteristics of the engineered nanomaterials be measured and differentiated from those of natural or incidental nanoparticles in the environment?
Can the airborne levels of engineered nanoparticles be quantified?
What are the applicable reporting limits of the methods used?
Are the airborne engineered nanoparticles well dispersed, agglomerated/aggregated particles, or bound in another matrix?
What parameters need to be evaluated when assessing airborne particle measurements (for example, particle count, particle size, surface area or mass metrics)?
What are the costs?

In many instances, traditional mass-based sampling and laboratory analysis techniques may not be suitable for evaluating airborne engineered nanoparticulate levels because of detection limit issues or because the methods are not nanoparticulate-specific. For many nanomaterials, it is postulated that the surface area, not the mass, determines toxicity⁽⁴⁾. One approach for evaluating the presence or absence of engineered nanoparticles is to use a direct read instrument, such as a handheld condensation particle counter (CPC), to survey particle concentrations at various locations. Total particle counts in the area can be compared and indexed to background levels and from process to process. The direct read instrumentation could be used to screen for areas of interest that may be suitable for obtaining integrated air samples on filters or impaction substrates for further study.

The integrated air samples can be prepared and analyzed by high resolution transmission electron microscopy (TEM) or scanning electron microscopy (SEM) methods to evaluate the presence or absence of engineered nanoparticles in the air. TEM/SEM methods can also be used to obtain information pertaining to chemistry, morphology, crystallography, particle associations (for example, agglomerations/aggregate particles or matrix associations) and abundance. Figures 1 through 7 illustrate examples of naturally occurring, incidental, and engineered nanoparticles obtained using SEM and TEM techniques.

Direct Read Instruments

Direct read instrumentation can provide instantaneous feedback to workers and bystanders to determine whether a work process is "in control" or results in elevated readings. Users should understand that direct read instruments acquire data for all particles within a given size range and cannot typically be applied to measure only specific engineered nanoparticles. Furthermore, high and/or variable concentrations of other nanoparticles, such as those in an industrial setting, can overwhelm the instruments or result in unsuitable data. Background levels of nanosized particles or contributing particles from other nearby activities can interfere with measurements and should be considered when evaluating results.

Following are some of the direct read instruments commercially available for air sampling for particulate:

Light scattering photometers are portable instruments report results on a mass per unit volume basis, such as milligrams per cubic meter of air. Measurements are typically applicable for particles that range from 0.1 to 10 micrometers in size.

Optical particle counters (OPC) are portable instruments that report results on a particle count per unit volume of air in multiple size ranges (typically five or six channels). Measurements are typically applicable for particles that range from 0.3 to 10 micrometers in size.

Condensation particle counters (CPC) are portable instruments that report results on a particle count per unit volume of air. Measurements are typically applicable for particles that range from 10 nanometers to 1 micron in size.

Scanning mobility particle sizers (SMPS) are larger, less portable and more expensive than handheld instruments. Research organizations use SMPS systems to measure the electrical mobility diameter of particles ranging from 2.5 nanometers to 1 micron in size with high resolution and accuracy. SMPS systems require more training to operate and contain a radioactive source, which may discourage their use at some facilities.

Fast mobility particle sizers (FMPS) are relatively large and costly. FMPS systems are integrated into a single "box" and have a fast response time (size distribution every second) which can be useful in recording releases of particles that range from around 6 to 560 nanometers in size. FMPS systems are lower-resolution instruments than SMPS systems and do not contain a radioactive source.

Surface area particle monitors measure surface area concentrations on a unit volume of air basis. Because industry professions are primarily concerned with the surface area associated with smaller nanometer-sized particles, these instruments use a cyclone to stop larger particles from entering. Surface area monitors typically measure aerosols in the range of 10 nanometers to 1 micron.

Integrated Air Sampling and Electron Microscopy Analysis

Prior to employing electron microscopy methods, one of the first considerations is to obtain representative specimens of bulk source materials of the engineered nanoparticles. If bulk materials are not available, obtain source area air samples in close proximity to areas where engineered nanoparticles are being generated. Evaluate the source samples and perform an initial examination of the engineered nanoparticulate using electron microscopy. This information can be used as a "standard" or reference material for future analyses. Evaluate the source particulates to identify unique characteristics that can be used to establish material-specific analysis protocols.

Multiple sampling methods can be used to yield a specimen suitable for TEM or SEM analysis. Open-faced filter sampling is arguably the easiest and most straightforward method. Polycarbonate (often preferred especially for SEM studies) or mixed cellulose ester filters can be used to perform an initial sampling study.

Historically, filter-based sampling methods have been used to sample for high aspect ratio nanoparticles, such as chrysotile asbestos fibers, which are naturally occurring magnesium- and silicon-containing nanotubes. To prepare and analyze a filter or substrate for TEM or SEM analysis, the particulate must be loaded properly. Trial and error using multiple sampling flow rates and times may be necessary to obtain filters suitable for examination by electron microscopy.

In addition to open-faced filter sampling, samples can also be obtained using size-selective sampling devices (for example, cyclones, elutriators, and cascade impactors) to deposit particulate on impaction substrates. Size-selective sampling may be desirable for separating airborne particles based on aerodynamic mass to evaluate different size fractions of materials in the air. Sampling techniques such as electrostatic or thermal precipitators are also available to deposit particles directly on a TEM grid or SEM stub for examination.

When employing electron microscopy methods to evaluate samples, the objectives of the analyses must be understood. Following sample preparation, perform a preliminary evaluation to ensure that the sample is suitable for analysis. Examine numerous areas of the prepared sample for nanoparticles. The characteristics of standards or other appropriate reference samples should be used to determine the presence of engineered nanoparticles. More detailed TEM or SEM analyses can be performed based on material- or project-specific protocols.

Selecting appropriate analytical instrumentation is also important for nanoparticulate studies. Incorporating modern high-resolution electron microscopes such as scanning transmission electron microscopes (STEM) or other state-of-the-art high resolution TEMs may be necessary. These instruments can be equipped to image particle surfaces, acquire elemental maps, determine elemental composition, and obtain internal structure and crystallographic information on nanoparticles.

Disclaimer

Many options are available to industrial hygiene and ESH professionals to protect personnel and evaluate engineered nanoparticles. This article is intended to stimulate discussions within the IH community and is by no means a comprehensive picture of the issues facing those who work with engineered nanoparticles. Even more considerations will be contemplated in the future as new information and instrumentation becomes available in the nanotechnology fields.

References

1. Department of Energy Nanoscale Science Research Centers: Department of Energy Nanoscale Science Research Centers Approach to Nanomaterial ES&H, Revision 3a - May 2008. [Online] Available at orise.orau.gov/ihos/Nanotechnology/nanotech_DOE_Nanoscale_SC.html.
2. NIOSH: Approaches to Safe Nanotechnology: An information exchange with NIOSH: July 2006. [Online] Available at www.cdc.gov/niosh/topics/nanotech/safenano/control.html.
3. ASTM International: Standard Guide for Handling Unbound Engineered Nanoscale Particles in Occupational Settings, ASTM E2535-07.
4. Kelly, Richard J.: "Occupational Medicine Implications of Engineered Nanoscale Particulate Matter," Journal of Chemical Health and Safety, January/February 2009.

Keith P. Rickabaugh, MBA, BS, is the technical director of materials and analytical services at RJ Lee Group, Inc. He can be reached at krickabaugh@rjlg.com.

Randy Ogle, MS, CIH, CSP, CHMM, is the operations manager (retired), US DOE Oak Ridge National Laboratory's Center for Nanophase Materials Sciences. He can be reached at safenano@gmail.com.