An opinion piece published in Fibers this month by Camarero-Espinosa and colleagues highlighted the tremendous potential of cellulose nanocrystals (CNCs) for a wide range of consumer applications. However, they also concluded that for certain endpoints, there remains a lack of knowledge on the safety of cellulose nanocrystals and suggested a path forward for the nanotoxicology community to address these gaps and holistically demonstrate their safety.

The authors emphasized that so far, no adverse acute effects from CNC exposure has been reported when using realistic concentrations. Further, the widely studied bulk forms of cellulose, such as cellulose dust (>10uM) and microfibrillated cellulose, show limited adverse effects. And although there have been studies emerging attempting to address these knowledge gaps for CNCs, they have many shortcomings, and offer little to further our knowledge on CNC safety. The authors highlight the following points for moving the field forward and adequately assessing human health risks:

• Characterization: we need reliable and representative methods to characterize CNCs; as well as characterization of the released material at important stages in its life cycle.
• Realistic dosing: studies need to use realistic doses to adequately assess hazard (and current practice of overload conditions needs to be avoided). We also need to assess and quantify what realistic exposures to CNC are comprised of at important life-cycle stages
• Hazard assessment: we need to further our understanding of the acute and chronic effects of CNC exposure (especially for occupational exposures); this assessment needs to include an understanding of biomolecular/biochemical mechanisms underlying and adverse effects observed.
• Relate to structure: given the multitude of CNCs emerging with different chemistries, shapes and production methods, our understanding needs to link effects observed to the physical and chemical characteristics of each CNC formulation.