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3 Critical Questions for Understanding Human and Environmental Effects of Engineered Nanomaterials
Pages 70-106

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From page 70...
... Figure 3-1 presents a source-toresponse paradigm that the committee used to organize and to identify the gaps and corresponding critical research questions. The boxes above the arrow generally track the life cycle of an ENM.
From page 71...
... Occupational exposure to ENMs is likely, given the extensive research enterprise and burgeoning startup business community. Inhalation exposure in manufacturing may occur if processes rely on gas-phase production of materials or if materials are aerosolized.
From page 72...
...  Research gaps concerning the in vivo evaluation of ENMs, particularly for chronic exposures and their impact on physiologic or biochemical endpoints.1  Gaps in understanding low-level environmental exposure to ENMs and their impact on organisms through changes in development, reproduction, and growth. While this is not a complete list, those topics represent conclusions reached in multiple synthesis reports over the last few years.
From page 73...
... The focus on systematic modeling has developed as investigators have grappled with the challenges of managing many types of nanomaterials, of formulations, of surface coatings, of delivery or packaging systems, and of exposure routes. The sheer number of possible variations makes conventional testing paradigms impractical.
From page 74...
... Adapted from ICON 2011. RESEARCH-GAP ANALYSIS AND IDENTIFICATION OF CRITICAL RESEARCH QUESTIONS Figure 3-1 is used in this section to structure consideration of the central research questions with major issues highlighted in boldface and mostly formulated as research questions.
From page 75...
... The research on specific material types should be continually revisited and informed through regular surveys of nanomaterial production and use patterns. What are the maximum anticipated amounts of exposures to ENM sources to which workers, consumers, and ecosystems could be exposed?
From page 76...
... More important, there is no information on the fraction of TABLE 3-2 Examples of Common Nanoscale Materials and Their Applicationsa Features and Types Example Products Fullerenes C60, carbon nanotubes, graphene Conductive films, fuel cells, composites, cosmetics Ceramics Iron oxides, ceria, titania Photocatalysts, magnetic data storage, window coatings, sun-screens, paint Metals Silver, gold, platinum Antimicrobial fabrics, oxidation catalysts, sensor elements Quantum Dots Cadmium chalcogenides Solar cells, diodes, biologic markers Polymers Copolymer assemblies, Coatings, rheologic control, dendrimers drug delivery a There is little information on the relative exposure to these different materials or their products.
From page 77...
... Inhalation is the most studied pathway; research on the effects of inhaling particles in the ultrafine size range long antedated the emergence of nanotechnology, and commercial instruments are available for detecting submicrometer ambient particles. For example, when measuring airborne engineered nanoparticles, equipment such as the Scanning Mobility Particle Sizer or Fast Mobility Particle Sizer can be used (McMurry 2000; Asbach et al.
From page 78...
... . The agglomeration-aggregation3 state of ENMs deep in the respiratory tract is not well understood and is related to the modifications of the ENM surface induced by the lung lining fluid and along translocation pathways.
From page 79...
... . Critical research questions include, What is the propensity of ENMs to survive in the gastrointestinal tract, particularly the acidic gastric milieu, as particles?
From page 80...
... . A critical research question is, What are the nature and implications of biomolecular modifications of ENMs?
From page 81...
... . These processes will affect the organisms that are likely to be exposed, the exposure routes, and the effects of exposure.
From page 82...
... It is unclear how sulfidation or aggregation of silver nanoparticles affects their rate of dissolution and persistence in the environment. Although the simple reaction chemistry of many of the most common ENMs is established, the quantitation of the dissolution rate and dependence on environmental conditions remains a critical research gap.
From page 83...
... can mitigate ENM exposure. A continuing research theme is the systematic linkage between ENM properties and their deposition and transport behavior in model and real porous media.
From page 84...
... A second approach builds mechanistic models based on fundamental processes affecting the behavior of ENMs in natural systems. Identifying the relevant processes should be possible in accordance with principles of colloidal science and an understanding, albeit limited, of the behavior of ENMs in environmental media.
From page 85...
... When designing animal studies, researchers are challenged in extrapolating findings to real-world human exposure to ENMs. For inhalation studies, this includes not only ensuring that the physical form of the aerosol (for example, agglomeration state and particle size distribution)
From page 86...
... Two critical research needs are to refine inhalation exposure and deposition models and to develop similar models for ingestion and dermal exposure. Virtually all analyses of research gaps in this regard have highlighted the importance of validating and linking in vitro and in vivo studies of ENMs.
From page 87...
... Knowledge of the biodistribution of nanoparticles after inhalation, oral, or dermal uptake is essential for identifying specific organs that may be targeted, including injury mechanisms, and designing the toxicity assays that best represent the exposures and mechanisms of toxicity. That aspect of nanotechnologyrelated EHS research has not been extensively explored, in part because labels for tracking ENMs require additional development to ensure their stability in vivo.
From page 88...
... Although many issues in this discussion are relevant to both ENM sources and ENM transformations, they are discussed here because of their relevance to biologic settings. There is a need to understand the potential for ENMs to accumulate in particular environmental compartments and to determine the area over which ENMs are distributed.
From page 89...
... Strong attachment of ENMs to biosolids may suggest that terrestrial exposure from biosolids that are spread on croplands is a greater source of ENMs than aquatic exposure to ENMs from wastewatertreatment plant effluent. Such distribution data can also be used to allocate ENM sources to their appropriate environmental compartments better, but this requires an ability to measure and characterize ENMs in complex environmental matrices -- a research issue highlighted in Chapter 4.
From page 90...
... Organism and Ecosystem Effects of Engineered Nanomaterials The responses of humans, other organisms, and the larger ecosystem to ENMs are central to understanding potential risks. Hazard assessments involving single organisms or in vitro toxicity assays have been the focus of research in this field, and there have been many in vitro and in vivo studies of various cell lines and organisms.
From page 91...
... that represent specific exposure routes and validation of results from in vitro studies with responses from relevant in vivo studies. This research is vital for developing high-throughput screening strategies for ENMs.
From page 92...
... Comparison of the correlations between in vitro and in vivo responses -- with in vivo data as the standard -- is needed. The lower, bidirectional arrows refer to the dosimetric correlations between in vitro/in vivo animals and in vivo animals/in vivo humans with the goal of informing the design of in vivo animal studies by using available human exposure data and dose–response information from animal studies to compare with human data.
From page 93...
... The inability to predict such effects creates great uncertainty regarding the potential effects of ENMs on the ecosystem. Gaps in Data on Ecologic Effects of Engineered Nanomaterials Numerous standard screening-level toxicity tests for specific aquatic and terrestrial organisms have been proposed for evaluating the effects of ENMs.
From page 94...
... . Leveraging research advances to include key ecologic receptors may help to correlate ENM properties with their potential for ecologic damage.
From page 95...
... and after low-dose chronic exposure. Because ENMs will probably exist at very low concentrations in the environment and will persist, low-level chronic exposure is the most likely scenario.
From page 96...
... Common Issues in Human Health and Ecologic Effects Research Issues that cut across human and ecologic health include determining the potential mechanisms of toxicity of nanomaterials and how they vary with ENM composition and dose, including developing data so as to correlate in vitro and in vivo responses; understanding effects of chronic exposure to nanomaterials; and obtaining data on multiple end points that precede or do not result in death of cells or organisms. There are also some common issues regarding experimental design and methods.
From page 97...
... However, measurements are needed to construct and validate exposure and toxicity models. Data on all aspects of EHS research regarding ENM properties, processes, and model validation should be collected and stored in a manner that enables data mining and integration with bioinformatic models.
From page 98...
... How do ENM properties influence toxicologic mechanisms of action? Ecosystem Health How can toxicity mechanisms for ENMs be better understood?
From page 99...
... , and cell membranes. The tendency of an ENM to attach to a surface affects aggregation, mobility in porous media, and cellular uptake, which are described in exposure models.
From page 100...
... 2005. Effect of single wall carbon nanotubes on human HEK293 cells.
From page 101...
... 2007. Biodistribution of functionalized multiwall carbon nanotubes in mice.
From page 102...
... 2009. Inter-comparison of a Fast Mobility Particle Sizer and a Scanning Mobility Particle Sizer incorporating an ultrafine water-based conden sation particle counter.
From page 103...
... 2004. Exposure to carbon nanotube material: Aerosol release during the handling of unrefined single-walled carbon nanotube material.
From page 104...
... 2010. Multi-walled carbon nanotubes (Baytubes)
From page 105...
... 2008. Aggregation kinetics of multiwalled carbon nanotubes in aquatic systems: Measurements and environmental implica tions.
From page 106...
... 2009. Charac terization and evaluation of nanoparticle release during the synthesis of single walled and multi-walled carbon nanotubes by chemical vapor deposition.


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