Abstract
Hazard studies of “as-produced” nanomaterials are increasingly available, yet a critical gap exists in exposure science that may impede safe development of nanomaterials. The gap is that we do not understand what is actually released because nanomaterials can change when released in ways that are not understood. We also generally do not have methods capable of quantitatively measuring what is released to support dose assessment. This review presents a case study of multi-walled carbon nanotubes (MWCNTs) for the measurement challenge to bridge this gap. As the use and value of MWCNTs increases, methods to measure what is released in ways relevant to risk evaluation are critically needed if products containing these materials are to be economically, environmentally, and socially sustainable. This review draws on the input of over 50 experts engaged in a program of workshops and technical report writing to address the release of MWCNTs from nanocomposite materials across their life cycle. The expert analyses reveals that new and sophisticated methods are required to measure and assess MWCNT exposures for realistic exposure scenarios. Furthermore, method requirements vary with the materials and conditions of release across life cycle stages of products. While review shows that the likelihood of significant release of MWCNTs appears to be low for many stages of composite life cycle, measurement methods are needed so that exposures from MWCNT-composites are understood and managed. In addition, there is an immediate need to refocus attention from study of “as-produced” nanomaterials to coordinated research on actual release scenarios.
Highlights
Developers of practical and beneficial products containing engineered nanomaterials lack critical information for nanomaterial use that is needed to align innovation goals with sustainable, safe product development.[1]
This state-of-the-science review for multi-walled carbon nanotubes (MWCNTs) in polymers highlights the disconnect between asproduced MWCNTs with much studied hazards and the more realistic polydisperse fragments released from nano-enabled products made of MWCNT-composites
While releases do not necessarily correlate to the quantity of exposure because there may be other mitigating factors, the quantity and characteristics of the materials released from matrices containing nanomaterials do need to be addressed during risk assessment and risk management, including assessment of the mechanism of release for each phase of the product life cycle
Summary
Developers of practical and beneficial products containing engineered nanomaterials lack critical information for nanomaterial use that is needed to align innovation goals with sustainable, safe product development.[1]. Evaluating a life cycle stage with high potential for consumer contact could be accomplished by a simple demonstration of a lack of physical opportunity for release (e.g., sealed components in a display screen), whereas specific doi:10.1088/1742-6596/617/1/012026 information on the magnitude and nature of long-term release from those same components may be needed to understand contributions to downstream or downwind receptors at EOL disposal Both physical and chemical mechanisms of release can further affect the specific release potential for nanomaterials added to composites because they can influence whether the nanomaterial remains embedded or is transformed during the release (Figure 3).[7,8,9,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55] Release mechanisms can be categorized based on the driving forces that can cause the release of MWCNTs throughout a product life cycle, such as mechanical stress, chemical processes (e.g., hydrolysis and photolysis), and incineration through human and environmental processes.[3] The use of life cycle concepts combined with an understanding of the driving forces provides a framework that enables the occurrence of particular mechanisms and their potential effect on nanomaterial release to be mapped out. Accelerated dry or wet weathering (ISO4892), followed by immersion to induce release into water, detected by AUC, TEM, EDX, LD, XPS
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