Phase 1: Nanomaterial Selection
The NanoRelease Steering Committee (SC) is composed of risk management experts from government, industry, nongovernmental organizations, and international organizations. Committee members deliberated over a 9-month period to identify potential nanomaterials and release methods for further study. More than 20 materials were identified and grouped into 3 priority groups. After conducting an extensive evaluation as well as ranking and voting on the materials, the SC narrowed the list of nanomaterials to either nano-silver (n-Ag) or multi-walled carbon nanotubes (MWCNTs).
2011 STEERING COMMITTEE WORKSHOP
Forty-five experts from academia, industry, and US and Canadian government agencies attended a May 10–11, 2011 workshop aimed to refine the project objectives, select the material that will be used to develop methods to measure release, and select and charge experts to develop white papers that will inform the development of a state-of-the-science document and workplan for “Phase 3” methods testing, development, and proof of utility for articles in commerce.
SELECTION OF THE FIRST TOP-PRIORITY NANOMATERIAL
After considerable discussion, the SC selected MWCNTs embedded within polymer matrices as the first nanomaterial to carry forward to the next phases of the project. The next steps include recruiting experts to develop white papers on several topics, convening a workshop to gather feedback on the resulting documents, and creating the state-of-the-science document and Phase 3 work plan.
Phase 2: Methods Evaluation
STATE OF THE SCIENCE
Expert Task Groups are formed for Phase 2 to develop white papers on the state of the science related to three aspects of the Project: (1) Methods; (2) Materials Characterization; and (3) Release Scenarios. The focus of Task Group 1 will be determined by selection of most likely scenarios by Task Group 3, and the key properties of the selected nanomaterial-product as determined by Task Group 2.
MWCNTs in Polymer
The current methods focus on multi-walled carbon nanotubes (MWCNTs) embedded in polymer matrices. One goal of Phase 2 is to identify existing methods and/or improve or develop new methods to detect and characterize MWCNTs released from widely-used consumer articles such as tennis rackets and fabrics throughout the articles’ lifecycles. These methods will be evaluated in Phase 3 of the Project through inter-laboratory testing to refine the measurement procedures and thus ensure reproducible data. Applicability of the methods to other MWCNT-product formulations used in other consumer articles will be evaluated. Further, the methods may be useful to guide design, development, and testing of other nanomaterial products and articles, and thus assess the potential for release, exposure, and subsequent risks. Ideally, the methods would be the basis of consensus documentary standards from standards development organizations such as ASTM and ISO.
There are two stages of test methods for the detection and characterization MWCNTs released from products and articles by various means such as abrasion and incineration. The first stage, Tier 1, involves the use of “master batches” of products designed to have varying release potentials of MWCNTs from low to high that represent a range of products used in consumer articles. The second stage, Tier 2, involves the detection and characterization of released. As shown in Phase 3, a detailed graphic describing the Tier 1 and Tier 2 testing process is available below.
After the white papers are completed, a workshop has convened to facilitate feedback on the documents.
Phase 3: Interlaboratory Studies
METHODS DEVELOPMENT AND REFINEMENT
Interlaboratory studies will be conducted in Phase 3 to develop methodologies identified in Phase 2. If we are successful, the resultant methods will be widely used to assess the potential for release and feed into exposure and subsequent risk evaluations. The methods will also be useful to guide design, development, and testing of nanomaterial products. Ideally, these methods would be the basis of consensus documentary standards from standards development organizations.
Phase 3 of the project will conduct testing and methods development using an interlaboratory testing approach, in which US and Canadian government, industry, and academic laboratories are convened using a “cooperative research and development agreement” approach often used by US government agencies to enable technology transfer between public and private sectors.
There are two stages of test methods for the detection and characterization MWCNTs released from products and articles by various means such as abrasion and incineration. The first stage, Tier 1, involves the use of “master batches” of products designed to have varying release potentials of MWCNTs from low to high that represent a range of products used in consumer articles. The second stage, Tier 2, involves the detection and characterization of released MWCNTs from actual consumer articles.
TIER 1 AND TIER 2 TESTING
For purposes of discussion here, an “article” is something that is made and sold in commerce. In common parlance this is often referred to a “finished product”.
The legal definition an “article” in the U.S. Toxic Substances Control Act is:
“a manufactured item (1) which is formed to a specific shape or design during manufacture, (2) which has end-use function(s) depending in whole or in part upon its shape or design during end use, and (3) which has either no change of chemical composition during its end use or only those changes of composition that have no commercial purpose separate from that of an article, and that results from a chemical reaction that occurs upon end use of other chemical substances, mixtures, or articles.”
In terms of the value chain, U.S. regulators refer to the precursor materials that are made into articles as either “chemical substances” or “products”. For example, carbon nanotubes can be sold in a free form (the powder in the above diagram) for research purposes and this would be referred to as a product. Similarly, carbon nanotubes can be mixed with plastic (the pellets in the above diagram) and sold as a “master batch” to subsequent manufacturers and this master batch would also be called a product in U.S. regulatory terms. The subsequent manufacturers would use the master batch to mix with other materials to make an “intermediate” product or “pre-preg” which can then be sold again or made into a finished product, these would be called articles.
Image source: Left and middle images courtesy of Nanocyl with permission.