Evaluation of Unbound Engineered Nanoparticles from a Worker Exposure and Environmental Release Perspective

Nanotechnology and the use of unbound engineered nanoparticles (UNP) is a rapidly developing area of material science. Unbound engineered nanoparticles are defined as engineered nanoparticles that are not contained within a matrix that would prevent the nanoparticles from being mobile and a potential source of exposure. At this time there are no regulatory environmental release limits or worker exposure limits for unbound engineered nanoparticles. Some preliminary consensus standards have been issued, but they are still under development by various organizations.

In an effort to evaluate worker exposure and potential environmental release of unbound engineered nanoparticles at Lawrence Berkeley National Laboratory, a multi-phase pilot study was initiated in the summer of 2009^1,2. RJ Lee Group, Inc. was retained to assist in the design, setup, and implementation of the study. The goals of the pilot study are to comply with Department of Energy (DOE) Notice N456.1, The Safe Handling of Unbound Engineered Nanoparticles³ and meet the requirements of the DOE Nanoscale Science Research Centers Approach to Nanoscale ES&H⁴.

What is Control Banding

A control banding approach is being used to provide guidance on risk management of UNP at Lawrence Berkeley National Laboratory. Originally developed in the pharmaceutical industry, control banding is a qualitative method for summarizing risks and controls⁵. It is a concept that is applicable to the field of engineered nanomaterials where there is incomplete information on hazard and exposure^6,7,8. Control banding utilizes basic characteristics of a process and its material(s) to determine a generalized risk level, either environmental or occupational.

This information can then be matched to a level of control best suited for the process. The outcome of the control banding process suggests or helps define the appropriate level of control for a process. When the control is appropriate for the risk, the hazard is successfully mitigated. Studies indicate that control banding is highly successful at determining adequate controls when validated by subsequent professional evaluations and workplace monitoring⁹. The control banding process being employed in this pilot study is based on the following algorithm:

The Worker/Environmental Hazard categories are based primarily on risk attributes such as dustiness, chemistry, and suspected toxicity (low, medium, high, very high/unknown). The Release/Exposure Probability categories are based on the ability of a material to become dispersed (unlikely, low, likely, probable). The Risk (Degree of Hazard) Level rankings range from relatively safe, 1A to the highest degree of risk, 4D, depending on the categories determined above.

The level of control for a process should be directly matched to the risk; that is, a low level of control is generally matched to a low level of risk, whereas higher risk indicates the need for a higher level of control. Controls may exceed the level of risk but should not be less than the level indicated by the risk. The preliminary control bands developed for Lawrence Berkeley National Laboratory illustrating the relationship of the probability of release/exposure to potential toxicity or severity are shown in a matrix form in Figure 1.

Figure 1. LBNL Preliminary Control Banding Matrix.

Lawrence Berkeley National Laboratory Pilot Study

To establish preliminary control bands, Phase I of the project involved discussions with the researchers and observation of processes involving fume hoods, glove boxes, counter tops and ablation systems. In addition, a key component of Phase I was the characterization of the starting (source) UNP materials. Samples of UNP materials used in process activities were obtained from the researchers, and these samples were analyzed using ICP and/or electron microscopy to establish source signatures of the various starting UNP materials.

For instance, in one laboratory gold nanorods are being studied for use in sensor applications. The milligram quantities of input material is obtained in an aqueous solution and manipulated within a functional laboratory exhaust hood. The source material was analyzed in a high-resolution scanning electron microscope (SEM) and found to be primarily rod-shaped particles approximately 20 nanometers in diameter and approximately 50 nanometers in length, as shown in Figure 2.

Figure 2. Secondary electron microscopy images of gold nanorods analyzed in a Hitachi S-5500 high resolution SEM.

The Phase II study activities involved the development of preliminary control bands. Based on the characterization of the source material as described for the gold nanorods, a review of process activities, and an assumed toxicity, a table of risk attributes specific to the material was generated. The table of risk attributes for the gold nanorods is shown in Table 1. A preliminary control band was then established for this process, as shown in Table 2.

Table 1. Risk Attributes for Gold Nanorods

Table 2. Preliminary Control Bands for Gold Nanorods

A preliminary control level II (refer to Fig. 1) was assigned to this process based on the category 2 release/exposure probability and category C worker/environmental hazard. Lawrence Berkeley National Laboratory is performing research activities using this material with level II controls in place for this process. Thus, the current level of controls for this process conforms to the control level indicated by the preliminary control band.

In Phase III, the preliminary control bands will be evaluated further and modified, as appropriate, based on data obtained through process and worker exposure sampling. The sampling methodology in Phase III will incorporate both real time particle counters and filtration-based particle collection methods.

Summary

Nanotechnology represents the next frontier in materials science with seemingly unlimited opportunities. Yet there is concern related to the potential toxicity associated with engineered particles in the nano size range¹⁰. We have built a foundation in research methods, characterization techniques, analytical instrumentation, and control strategies.

This work advances the knowledge base and experience to move forward in a safe manner in the emerging field of nanotechnology. The work being performed at Lawrence Berkeley National Laboratory builds on this foundation and puts into practice a methodology that can be used to reduce risks to the worker and the environment related to the use of nanomaterials.

Acknowledgements

The authors would like to acknowlege Leo Banchik, Jay James, Guy Kelley, Don Lucas, Ron Pauer and Tim Roberts at Lawrence Berkeley National Laboratory for their contributions to the study.

References

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2. Casuccio, G., Ogle, R., Wahl, L., and Pauer, R., "Worker and Environmental Assessment of Potential Unbound Engineered Nanoparticles Releases: Phase II Final Report," RJ Lee Group, Inc., and Lawrence Berkeley National Laboratory, September 2009.
3. Department of Energy, The Safe Handling of Unbound Engineered Nanoparticles, DOE N456.1, 5 January 2009.
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