Zinc oxide nanoparticles (n-ZnO) are one of the most ever-increasing utilized nanomaterials in consumer products. Due to their antibacterial properties and superior efficiency in absorbing ultraviolet radiation, it is widely used as additives into food packaging and sunscreens. There is thus a need for scientific understanding of risks to health of adult populations associated with n-ZnO. However, in lack of inadequate data in characterizing hazard and exposure, there is a substantial uncertainty in risk assessment. In the present study, probabilistic approaches, including Monte Carlo and Bootstrap methods, were integrated to assess relative uncertainties and risks of n-ZnO to health of males and females. Two major exposure pathways, oral from food packaging and percutaneous from sunscreen-based comestics, were evaluated by considering uncertainty and variability contained in the exposure assessment. Given cumulative uncertainties of all the extrapolation factors, these results showed that the individual margin of exposure (IMoE) of n-ZnO exhibited minimal risk through oral exposure, with a minimum value of 786 for males and 96.2 for females (5% centile). However, within the entire range of IMoE values by Monte Carlo simulationthrough dermal exposure, the IMoE values in 11.45% of exposure scenarios for males and 18.87% for females were lower than the upper limit of the acceptable risk (IMoE≤1). Intra-, inter-species, and subacute-to-chronic extrapolation factors in the hazard assessment process contributed up to 97% of the uncertainty. These findings provided a scientific basis for understanding risks to health of adult polulations that could help allow regulatory acceptance of consumer products containing n-ZnO and highlighted the need for additional studies on hazard and exposure assessments of nanotechnologies.

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