Challenges for Evaluation of the Hed of Engineered Nanomaterials Safety by Linda J. Johnston, Norma GonzalezRojano, Kevin J. Wilkinson, and Baoshan Xing
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anotechnology has developed rapidly in the last two decades with significant effort focused on the development of nano-enabled materials with new or improved properties that offer solutions for current world challenges. The commercialization of products containing engineered nanomaterials (ENM) has progressed much more rapidly than the development of practical approaches to ensure their safe and sustainable use. The lack of adequate detection and characterization techniques and reproducible and validated methods for toxicological studies have been identified as major limitations. The rapid development of ENM of increasing complexity and diversity and concerns over the adequacy of existing regulations also contribute to safety concerns with these materials. The full potential of nanotechnology can only be realized when feasible, cost-effective strategies to ensure a safe-by-design approach, effective risk assessment approaches and appropriate regulatory guidelines are in place.
An IUPAC-sponsored Workshop on the Safety of Engineered Nanomaterials in Queretaro, Mexico in late 2017 aimed to foster a greater awareness of the challenges and identify future research needs that must be filled to develop a regulatory framework for nanomaterials. The workshop covered four topics: (1) Detection and characterization of ENM, (2) Transformation of ENM in consumer products and the environment, (3) Nanotoxicology methods and gaps for environmental health and safety (EHS) and (4) Challenges for metrology, risk assessment, and standardization. This article highlights the main challenges and potential solutions that were developed during the workshop (https://iupac.org/project/2016-045-2-700) and subsequently by the authors and published in a recent NanoImpact article [1].
First, the characterization of ENM is complex, compared to conventional chemicals, since many properties must be assessed (Figure 1) and it is not always clear which ones are important for a specific application. ENM properties can be separated into two categories: intrinsic properties such as size, surface area, and composition that do not depend on the medium or environment (“what they are”) and extrinsic properties such as surface chemistry and aggregation that depend on the environment and determine the fate and reactivity of the material (“where they go” and “what they do”). Methods are typically optimized for pristine ENM and may not be applicable to the required environmental or use conditions. In other cases validated protocols are missing or rarely used by the community. Second, many ENM properties are method-defined. For example, particle size can be assessed by more than ten different methods, each with its own range of applicability, theoretical basis and sensitivity. Particle size distributions may be based on intensity, number or mass and can be measured by either ensemble methods that interrogate the entire sample or by particle counting methods such as microscopy techniques. Selection of a fit-for-purpose method must consider the theoretical basis of the technique, method sensitivity and calibration, analyte concentration, sample matrix, potential ENM transformations, and the acceptable uncertainty for a specific application. Despite this complexity, there is an emerging consensus on the key properties that are necessary for
Detection and characterization of ENM The utility of many published studies on the synthesis, applications, and toxicology of ENM is limited by inadequate characterization and data reporting. These issues impact quality control during production of the materials and prevent inter-laboratory comparability for applications development and nanotoxicology studies. Several factors contribute to this problem.
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Chemistry International
January-March 2021
Figure. 1. Illustration of some of the ENM properties that must be characterized, reproduced with permission [1].
