Occupational Risk Assessment of Engineered Nanomaterials: Limits, Challenges and Opportunities

Background: The widespread application of nanotechnology in the last decades, the increasing likelihood of human exposure to nano-sized materials, together with the still limited knowledge concerning their toxicological profile, require a careful risk assessment, particularly in occupational settings. However, a specific "risk assessment paradigm" for these peculiar xenobiotics has not yet been defined. Objective: The aim of this review was to address those critical aspects that currently prevent the achievement of a suitable risk evaluation in order to point out priorities of research helpful to develop and implement an effective guidance for nano-risk assessment. Method: Literature search concerning NM physico-chemical characterization, toxicological behavior and exposure assessment strategies was analyzed to extrapolate opportunities, challenges and criticisms in the application of the general chemical risk assessment steps to the nano-sized toxicological field. Results: Uncertainties on the role of the physico-chemical properties in nanomaterial toxicity, the complexity in extrapolating dose-response relationships, and practical difficulties in measuring nanomaterial exposure emerged as challenging issues for the application of a traditional risk assessment approach to nano-sized exposures. Conclusion: Future investigations on these topics appear necessary to define an effective, nano-focused risk evaluation strategy that should be dynamically improved and verified as more substantial information become available. Such a suitable risk assessment process should provide adequate estimates of nanomaterial risks to guide the adoption of appropriate risk communication and management strategies for the protection and the safety of the workers.